Migrate tunnel related classes to tunnel/ Gradle module

Signed-off-by: Harsh Shandilya <me@msfjarvis.dev>

24 files changed, 3485 insertions, 0 deletions

diff --git a/tunnel/src/main/java/com/wireguard/android/backend/Backend.java b/tunnel/src/main/java/com/wireguard/android/backend/Backend.java
new file mode 100644
index 00000000..ed3a5ebd
--- /dev/null
+++ b/tunnel/src/main/java/com/wireguard/android/backend/Backend.java
@@ -0,0 +1,63 @@
+/*
+ * Copyright © 2017-2019 WireGuard LLC. All Rights Reserved.
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package com.wireguard.android.backend;
+
+import com.wireguard.config.Config;
+
+import java.util.Collection;
+import java.util.Set;
+
+import androidx.annotation.Nullable;
+
+/**
+ * Interface for implementations of the WireGuard secure network tunnel.
+ */
+
+public interface Backend {
+    /**
+     * Enumerate names of currently-running tunnels.
+     *
+     * @return The set of running tunnel names.
+     */
+    Set<String> getRunningTunnelNames();
+
+    /**
+     * Get the state of a tunnel.
+     *
+     * @param tunnel The tunnel to examine the state of.
+     * @return The state of the tunnel.
+     */
+    Tunnel.State getState(Tunnel tunnel) throws Exception;
+
+    /**
+     * Get statistics about traffic and errors on this tunnel. If the tunnel is not running, the
+     * statistics object will be filled with zero values.
+     *
+     * @param tunnel The tunnel to retrieve statistics for.
+     * @return The statistics for the tunnel.
+     */
+    Statistics getStatistics(Tunnel tunnel) throws Exception;
+
+    /**
+     * Determine version of underlying backend.
+     *
+     * @return The version of the backend.
+     * @throws Exception
+     */
+    String getVersion() throws Exception;
+
+    /**
+     * Set the state of a tunnel, updating it's configuration. If the tunnel is already up, config
+     * may update the running configuration; config may be null when setting the tunnel down.
+     *
+     * @param tunnel The tunnel to control the state of.
+     * @param state  The new state for this tunnel. Must be {@code UP}, {@code DOWN}, or
+     *               {@code TOGGLE}.
+     * @param config The configuration for this tunnel, may be null if state is {@code DOWN}.
+     * @return The updated state of the tunnel.
+     */
+    Tunnel.State setState(Tunnel tunnel, Tunnel.State state, @Nullable Config config) throws Exception;
+}
diff --git a/tunnel/src/main/java/com/wireguard/android/backend/BackendException.java b/tunnel/src/main/java/com/wireguard/android/backend/BackendException.java
new file mode 100644
index 00000000..e1e8eaa9
--- /dev/null
+++ b/tunnel/src/main/java/com/wireguard/android/backend/BackendException.java
@@ -0,0 +1,30 @@
+/*
+ * Copyright © 2020 WireGuard LLC. All Rights Reserved.
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package com.wireguard.android.backend;
+
+public final class BackendException extends Exception {
+    public enum Reason {
+        UNKNOWN_KERNEL_MODULE_NAME,
+        WG_QUICK_CONFIG_ERROR_CODE,
+        TUNNEL_MISSING_CONFIG,
+        VPN_NOT_AUTHORIZED,
+        UNABLE_TO_START_VPN,
+        TUN_CREATION_ERROR,
+        GO_ACTIVATION_ERROR_CODE
+    }
+    private final Reason reason;
+    private final Object[] format;
+    public BackendException(final Reason reason, final Object ...format) {
+        this.reason = reason;
+        this.format = format;
+    }
+    public Reason getReason() {
+        return reason;
+    }
+    public Object[] getFormat() {
+        return format;
+    }
+}
diff --git a/tunnel/src/main/java/com/wireguard/android/backend/GoBackend.java b/tunnel/src/main/java/com/wireguard/android/backend/GoBackend.java
new file mode 100644
index 00000000..6ad5afa4
--- /dev/null
+++ b/tunnel/src/main/java/com/wireguard/android/backend/GoBackend.java
@@ -0,0 +1,292 @@
+/*
+ * Copyright © 2017-2019 WireGuard LLC. All Rights Reserved.
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package com.wireguard.android.backend;
+
+import android.content.Context;
+import android.content.Intent;
+import android.os.Build;
+import android.os.ParcelFileDescriptor;
+import androidx.annotation.Nullable;
+import androidx.collection.ArraySet;
+import android.util.Log;
+
+import com.wireguard.android.backend.BackendException.Reason;
+import com.wireguard.android.backend.Tunnel.State;
+import com.wireguard.android.util.SharedLibraryLoader;
+import com.wireguard.config.Config;
+import com.wireguard.config.InetNetwork;
+import com.wireguard.config.Peer;
+import com.wireguard.crypto.Key;
+import com.wireguard.crypto.KeyFormatException;
+
+import java.net.InetAddress;
+import java.util.Collections;
+import java.util.Set;
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.TimeoutException;
+
+import java9.util.concurrent.CompletableFuture;
+
+public final class GoBackend implements Backend {
+    private static final String TAG = "WireGuard/" + GoBackend.class.getSimpleName();
+    private static CompletableFuture<VpnService> vpnService = new CompletableFuture<>();
+    public interface AlwaysOnCallback {
+        void alwaysOnTriggered();
+    }
+    @Nullable private static AlwaysOnCallback alwaysOnCallback;
+    public static void setAlwaysOnCallback(AlwaysOnCallback cb) {
+        alwaysOnCallback = cb;
+    }
+
+    private final Context context;
+    @Nullable private Tunnel currentTunnel;
+    @Nullable private Config currentConfig;
+    private int currentTunnelHandle = -1;
+
+    public GoBackend(final Context context) {
+        SharedLibraryLoader.loadSharedLibrary(context, "wg-go");
+        this.context = context;
+    }
+
+    private static native String wgGetConfig(int handle);
+
+    private static native int wgGetSocketV4(int handle);
+
+    private static native int wgGetSocketV6(int handle);
+
+    private static native void wgTurnOff(int handle);
+
+    private static native int wgTurnOn(String ifName, int tunFd, String settings);
+
+    private static native String wgVersion();
+
+    @Override
+    public Set<String> getRunningTunnelNames() {
+        if (currentTunnel != null) {
+            final Set<String> runningTunnels = new ArraySet<>();
+            runningTunnels.add(currentTunnel.getName());
+            return runningTunnels;
+        }
+        return Collections.emptySet();
+    }
+
+    @Override
+    public State getState(final Tunnel tunnel) {
+        return currentTunnel == tunnel ? State.UP : State.DOWN;
+    }
+
+    @Override
+    public Statistics getStatistics(final Tunnel tunnel) {
+        final Statistics stats = new Statistics();
+        if (tunnel != currentTunnel) {
+            return stats;
+        }
+        final String config = wgGetConfig(currentTunnelHandle);
+        Key key = null;
+        long rx = 0, tx = 0;
+        for (final String line : config.split("\\n")) {
+            if (line.startsWith("public_key=")) {
+                if (key != null)
+                    stats.add(key, rx, tx);
+                rx = 0;
+                tx = 0;
+                try {
+                    key = Key.fromHex(line.substring(11));
+                } catch (final KeyFormatException ignored) {
+                    key = null;
+                }
+            } else if (line.startsWith("rx_bytes=")) {
+                if (key == null)
+                    continue;
+                try {
+                    rx = Long.parseLong(line.substring(9));
+                } catch (final NumberFormatException ignored) {
+                    rx = 0;
+                }
+            } else if (line.startsWith("tx_bytes=")) {
+                if (key == null)
+                    continue;
+                try {
+                    tx = Long.parseLong(line.substring(9));
+                } catch (final NumberFormatException ignored) {
+                    tx = 0;
+                }
+            }
+        }
+        if (key != null)
+            stats.add(key, rx, tx);
+        return stats;
+    }
+
+    @Override
+    public String getVersion() {
+        return wgVersion();
+    }
+
+    @Override
+    public State setState(final Tunnel tunnel, State state, @Nullable final Config config) throws Exception {
+        final State originalState = getState(tunnel);
+
+        if (state == State.TOGGLE)
+            state = originalState == State.UP ? State.DOWN : State.UP;
+        if (state == originalState && tunnel == currentTunnel && config == currentConfig)
+            return originalState;
+        if (state == State.UP) {
+            final Config originalConfig = currentConfig;
+            final Tunnel originalTunnel = currentTunnel;
+            if (currentTunnel != null)
+                setStateInternal(currentTunnel, null, State.DOWN);
+            try {
+                setStateInternal(tunnel, config, state);
+            } catch(final Exception e) {
+                if (originalTunnel != null)
+                    setStateInternal(originalTunnel, originalConfig, State.UP);
+                throw e;
+            }
+        } else if (state == State.DOWN && tunnel == currentTunnel) {
+            setStateInternal(tunnel, null, State.DOWN);
+        }
+        return getState(tunnel);
+    }
+
+    private void setStateInternal(final Tunnel tunnel, @Nullable final Config config, final State state)
+            throws Exception {
+        Log.i(TAG, "Bringing tunnel " + tunnel.getName() + " " + state);
+
+        if (state == State.UP) {
+            if (config == null)
+                throw new BackendException(Reason.TUNNEL_MISSING_CONFIG);
+
+            if (VpnService.prepare(context) != null)
+                throw new BackendException(Reason.VPN_NOT_AUTHORIZED);
+
+            final VpnService service;
+            if (!vpnService.isDone())
+                startVpnService();
+
+            try {
+                service = vpnService.get(2, TimeUnit.SECONDS);
+            } catch (final TimeoutException e) {
+                final Exception be = new BackendException(Reason.UNABLE_TO_START_VPN);
+                be.initCause(e);
+                throw be;
+            }
+            service.setOwner(this);
+
+            if (currentTunnelHandle != -1) {
+                Log.w(TAG, "Tunnel already up");
+                return;
+            }
+
+            // Build config
+            final String goConfig = config.toWgUserspaceString();
+
+            // Create the vpn tunnel with android API
+            final VpnService.Builder builder = service.getBuilder();
+            builder.setSession(tunnel.getName());
+
+            for (final String excludedApplication : config.getInterface().getExcludedApplications())
+                builder.addDisallowedApplication(excludedApplication);
+
+            for (final InetNetwork addr : config.getInterface().getAddresses())
+                builder.addAddress(addr.getAddress(), addr.getMask());
+
+            for (final InetAddress addr : config.getInterface().getDnsServers())
+                builder.addDnsServer(addr.getHostAddress());
+
+            for (final Peer peer : config.getPeers()) {
+                for (final InetNetwork addr : peer.getAllowedIps())
+                    builder.addRoute(addr.getAddress(), addr.getMask());
+            }
+
+            builder.setMtu(config.getInterface().getMtu().orElse(1280));
+
+            if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.Q)
+                builder.setMetered(false);
+            if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M)
+	        service.setUnderlyingNetworks(null);
+
+            builder.setBlocking(true);
+            try (final ParcelFileDescriptor tun = builder.establish()) {
+                if (tun == null)
+                    throw new BackendException(Reason.TUN_CREATION_ERROR);
+                Log.d(TAG, "Go backend v" + wgVersion());
+                currentTunnelHandle = wgTurnOn(tunnel.getName(), tun.detachFd(), goConfig);
+            }
+            if (currentTunnelHandle < 0)
+                throw new BackendException(Reason.GO_ACTIVATION_ERROR_CODE, currentTunnelHandle);
+
+            currentTunnel = tunnel;
+            currentConfig = config;
+
+            service.protect(wgGetSocketV4(currentTunnelHandle));
+            service.protect(wgGetSocketV6(currentTunnelHandle));
+        } else {
+            if (currentTunnelHandle == -1) {
+                Log.w(TAG, "Tunnel already down");
+                return;
+            }
+
+            wgTurnOff(currentTunnelHandle);
+            currentTunnel = null;
+            currentTunnelHandle = -1;
+            currentConfig = null;
+        }
+
+        tunnel.onStateChange(state);
+    }
+
+    private void startVpnService() {
+        Log.d(TAG, "Requesting to start VpnService");
+        context.startService(new Intent(context, VpnService.class));
+    }
+
+    public static class VpnService extends android.net.VpnService {
+        @Nullable private GoBackend owner;
+
+        public void setOwner(final GoBackend owner) {
+            this.owner = owner;
+        }
+
+        public Builder getBuilder() {
+            return new Builder();
+        }
+
+        @Override
+        public void onCreate() {
+            vpnService.complete(this);
+            super.onCreate();
+        }
+
+        @Override
+        public void onDestroy() {
+            if (owner != null) {
+                final Tunnel tunnel = owner.currentTunnel;
+                if (tunnel != null) {
+                    if (owner.currentTunnelHandle != -1)
+                        wgTurnOff(owner.currentTunnelHandle);
+                    owner.currentTunnel = null;
+                    owner.currentTunnelHandle = -1;
+                    owner.currentConfig = null;
+                    tunnel.onStateChange(State.DOWN);
+                }
+            }
+            vpnService = vpnService.newIncompleteFuture();
+            super.onDestroy();
+        }
+
+        @Override
+        public int onStartCommand(@Nullable final Intent intent, final int flags, final int startId) {
+            vpnService.complete(this);
+            if (intent == null || intent.getComponent() == null || !intent.getComponent().getPackageName().equals(getPackageName())) {
+                Log.d(TAG, "Service started by Always-on VPN feature");
+                if (alwaysOnCallback != null)
+                    alwaysOnCallback.alwaysOnTriggered();
+            }
+            return super.onStartCommand(intent, flags, startId);
+        }
+    }
+}
diff --git a/tunnel/src/main/java/com/wireguard/android/backend/Statistics.java b/tunnel/src/main/java/com/wireguard/android/backend/Statistics.java
new file mode 100644
index 00000000..2ca87d23
--- /dev/null
+++ b/tunnel/src/main/java/com/wireguard/android/backend/Statistics.java
@@ -0,0 +1,62 @@
+/*
+ * Copyright © 2020 WireGuard LLC. All Rights Reserved.
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package com.wireguard.android.backend;
+
+import android.os.SystemClock;
+import android.util.Pair;
+
+import com.wireguard.crypto.Key;
+
+import java.util.HashMap;
+import java.util.Map;
+
+public class Statistics {
+    private long lastTouched = SystemClock.elapsedRealtime();
+    private final Map<Key, Pair<Long, Long>> peerBytes = new HashMap<>();
+
+    Statistics() { }
+
+    void add(final Key key, final long rx, final long tx) {
+        peerBytes.put(key, Pair.create(rx, tx));
+        lastTouched = SystemClock.elapsedRealtime();
+    }
+
+    public boolean isStale() {
+        return SystemClock.elapsedRealtime() - lastTouched > 900;
+    }
+
+    public Key[] peers() {
+        return peerBytes.keySet().toArray(new Key[0]);
+    }
+
+    public long peerRx(final Key peer) {
+        if (!peerBytes.containsKey(peer))
+            return 0;
+        return peerBytes.get(peer).first;
+    }
+
+    public long peerTx(final Key peer) {
+        if (!peerBytes.containsKey(peer))
+            return 0;
+        return peerBytes.get(peer).second;
+    }
+
+    public long totalRx() {
+        long rx = 0;
+        for (final Pair<Long, Long> val : peerBytes.values()) {
+            rx += val.first;
+        }
+        return rx;
+    }
+
+    public long totalTx() {
+        long tx = 0;
+        for (final Pair<Long, Long> val : peerBytes.values()) {
+            tx += val.second;
+        }
+        return tx;
+    }
+}
diff --git a/tunnel/src/main/java/com/wireguard/android/backend/Tunnel.java b/tunnel/src/main/java/com/wireguard/android/backend/Tunnel.java
new file mode 100644
index 00000000..af2f59f7
--- /dev/null
+++ b/tunnel/src/main/java/com/wireguard/android/backend/Tunnel.java
@@ -0,0 +1,46 @@
+/*
+ * Copyright © 2020 WireGuard LLC. All Rights Reserved.
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package com.wireguard.android.backend;
+
+import java.util.regex.Pattern;
+
+/**
+ * Represents a WireGuard tunnel.
+ */
+
+public interface Tunnel {
+    enum State {
+        DOWN,
+        TOGGLE,
+        UP;
+
+        public static State of(final boolean running) {
+            return running ? UP : DOWN;
+        }
+    }
+
+    int NAME_MAX_LENGTH = 15;
+    Pattern NAME_PATTERN = Pattern.compile("[a-zA-Z0-9_=+.-]{1,15}");
+
+    static boolean isNameInvalid(final CharSequence name) {
+        return !NAME_PATTERN.matcher(name).matches();
+    }
+
+    /**
+     * Get the name of the tunnel, which should always pass the !isNameInvalid test.
+     *
+     * @return The name of the tunnel.
+     */
+    String getName();
+
+    /**
+     * React to a change in state of the tunnel. Should only be directly called by Backend.
+     *
+     * @param newState The new state of the tunnel.
+     * @return The new state of the tunnel.
+     */
+    void onStateChange(State newState);
+}
diff --git a/tunnel/src/main/java/com/wireguard/android/backend/WgQuickBackend.java b/tunnel/src/main/java/com/wireguard/android/backend/WgQuickBackend.java
new file mode 100644
index 00000000..9695aab7
--- /dev/null
+++ b/tunnel/src/main/java/com/wireguard/android/backend/WgQuickBackend.java
@@ -0,0 +1,158 @@
+/*
+ * Copyright © 2017-2019 WireGuard LLC. All Rights Reserved.
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package com.wireguard.android.backend;
+
+import androidx.annotation.Nullable;
+
+import android.content.Context;
+import android.util.Log;
+
+import com.wireguard.android.backend.BackendException.Reason;
+import com.wireguard.android.backend.Tunnel.State;
+import com.wireguard.android.util.RootShell;
+import com.wireguard.android.util.ToolsInstaller;
+import com.wireguard.config.Config;
+import com.wireguard.crypto.Key;
+
+import java.io.File;
+import java.io.FileOutputStream;
+import java.nio.charset.StandardCharsets;
+import java.util.ArrayList;
+import java.util.Collection;
+import java.util.Collections;
+import java.util.List;
+import java.util.Locale;
+import java.util.Map;
+import java.util.Objects;
+import java.util.Set;
+import java.util.HashMap;
+
+import java9.util.stream.Collectors;
+import java9.util.stream.Stream;
+
+/**
+ * WireGuard backend that uses {@code wg-quick} to implement tunnel configuration.
+ */
+
+public final class WgQuickBackend implements Backend {
+    private static final String TAG = "WireGuard/" + WgQuickBackend.class.getSimpleName();
+
+    private final RootShell rootShell;
+    private final ToolsInstaller toolsInstaller;
+    private final File localTemporaryDir;
+    private final Map<Tunnel, Config> runningConfigs = new HashMap<>();
+
+    public WgQuickBackend(final Context context, final RootShell rootShell, final ToolsInstaller toolsInstaller) {
+        localTemporaryDir = new File(context.getCacheDir(), "tmp");
+        this.rootShell = rootShell;
+        this.toolsInstaller = toolsInstaller;
+    }
+
+    @Override
+    public Set<String> getRunningTunnelNames() {
+        final List<String> output = new ArrayList<>();
+        // Don't throw an exception here or nothing will show up in the UI.
+        try {
+            toolsInstaller.ensureToolsAvailable();
+            if (rootShell.run(output, "wg show interfaces") != 0 || output.isEmpty())
+                return Collections.emptySet();
+        } catch (final Exception e) {
+            Log.w(TAG, "Unable to enumerate running tunnels", e);
+            return Collections.emptySet();
+        }
+        // wg puts all interface names on the same line. Split them into separate elements.
+        return Stream.of(output.get(0).split(" ")).collect(Collectors.toUnmodifiableSet());
+    }
+
+    @Override
+    public State getState(final Tunnel tunnel) {
+        return getRunningTunnelNames().contains(tunnel.getName()) ? State.UP : State.DOWN;
+    }
+
+    @Override
+    public Statistics getStatistics(final Tunnel tunnel) {
+        final Statistics stats = new Statistics();
+        final Collection<String> output = new ArrayList<>();
+        try {
+            if (rootShell.run(output, String.format("wg show '%s' transfer", tunnel.getName())) != 0)
+                return stats;
+        } catch (final Exception ignored) {
+            return stats;
+        }
+        for (final String line : output) {
+            final String[] parts = line.split("\\t");
+            if (parts.length != 3)
+                continue;
+            try {
+                stats.add(Key.fromBase64(parts[0]), Long.parseLong(parts[1]), Long.parseLong(parts[2]));
+            } catch (final Exception ignored) {
+            }
+        }
+        return stats;
+    }
+
+    @Override
+    public String getVersion() throws Exception {
+        final List<String> output = new ArrayList<>();
+        if (rootShell.run(output, "cat /sys/module/wireguard/version") != 0 || output.isEmpty())
+            throw new BackendException(Reason.UNKNOWN_KERNEL_MODULE_NAME);
+        return output.get(0);
+    }
+
+    @Override
+    public State setState(final Tunnel tunnel, State state, @Nullable final Config config) throws Exception {
+        final State originalState = getState(tunnel);
+        final Config originalConfig = runningConfigs.get(tunnel);
+
+        if (state == State.TOGGLE)
+            state = originalState == State.UP ? State.DOWN : State.UP;
+        if ((state == State.UP && originalState == State.UP && originalConfig != null && originalConfig == config) ||
+                (state == State.DOWN && originalState == State.DOWN))
+            return originalState;
+        if (state == State.UP) {
+            toolsInstaller.ensureToolsAvailable();
+            if (originalState == State.UP)
+                setStateInternal(tunnel, originalConfig == null ? config : originalConfig, State.DOWN);
+            try {
+                setStateInternal(tunnel, config, State.UP);
+            } catch(final Exception e) {
+                if (originalState == State.UP && originalConfig != null)
+                    setStateInternal(tunnel, originalConfig, State.UP);
+                throw e;
+            }
+        } else if (state == State.DOWN) {
+            setStateInternal(tunnel, originalConfig == null ? config : originalConfig, State.DOWN);
+        }
+        return state;
+    }
+
+    private void setStateInternal(final Tunnel tunnel, @Nullable final Config config, final State state) throws Exception {
+        Log.i(TAG, "Bringing tunnel " + tunnel.getName() + " " + state);
+
+        Objects.requireNonNull(config, "Trying to set state up with a null config");
+
+        final File tempFile = new File(localTemporaryDir, tunnel.getName() + ".conf");
+        try (final FileOutputStream stream = new FileOutputStream(tempFile, false)) {
+            stream.write(config.toWgQuickString().getBytes(StandardCharsets.UTF_8));
+        }
+        String command = String.format("wg-quick %s '%s'",
+                state.toString().toLowerCase(Locale.ENGLISH), tempFile.getAbsolutePath());
+        if (state == State.UP)
+            command = "cat /sys/module/wireguard/version && " + command;
+        final int result = rootShell.run(null, command);
+        // noinspection ResultOfMethodCallIgnored
+        tempFile.delete();
+        if (result != 0)
+            throw new BackendException(Reason.WG_QUICK_CONFIG_ERROR_CODE, result);
+
+        if (state == State.UP)
+            runningConfigs.put(tunnel, config);
+        else
+            runningConfigs.remove(tunnel);
+
+        tunnel.onStateChange(state);
+    }
+}
diff --git a/tunnel/src/main/java/com/wireguard/android/util/AsyncWorker.java b/tunnel/src/main/java/com/wireguard/android/util/AsyncWorker.java
new file mode 100644
index 00000000..1d041851
--- /dev/null
+++ b/tunnel/src/main/java/com/wireguard/android/util/AsyncWorker.java
@@ -0,0 +1,63 @@
+/*
+ * Copyright © 2017-2019 WireGuard LLC. All Rights Reserved.
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package com.wireguard.android.util;
+
+import android.os.Handler;
+
+import java.util.concurrent.Executor;
+
+import java9.util.concurrent.CompletableFuture;
+import java9.util.concurrent.CompletionStage;
+
+/**
+ * Helper class for running asynchronous tasks and ensuring they are completed on the main thread.
+ */
+
+public class AsyncWorker {
+    private final Executor executor;
+    private final Handler handler;
+
+    public AsyncWorker(final Executor executor, final Handler handler) {
+        this.executor = executor;
+        this.handler = handler;
+    }
+
+    public CompletionStage<Void> runAsync(final AsyncRunnable<?> runnable) {
+        final CompletableFuture<Void> future = new CompletableFuture<>();
+        executor.execute(() -> {
+            try {
+                runnable.run();
+                handler.post(() -> future.complete(null));
+            } catch (final Throwable t) {
+                handler.post(() -> future.completeExceptionally(t));
+            }
+        });
+        return future;
+    }
+
+    public <T> CompletionStage<T> supplyAsync(final AsyncSupplier<T, ?> supplier) {
+        final CompletableFuture<T> future = new CompletableFuture<>();
+        executor.execute(() -> {
+            try {
+                final T result = supplier.get();
+                handler.post(() -> future.complete(result));
+            } catch (final Throwable t) {
+                handler.post(() -> future.completeExceptionally(t));
+            }
+        });
+        return future;
+    }
+
+    @FunctionalInterface
+    public interface AsyncRunnable<E extends Throwable> {
+        void run() throws E;
+    }
+
+    @FunctionalInterface
+    public interface AsyncSupplier<T, E extends Throwable> {
+        T get() throws E;
+    }
+}
diff --git a/tunnel/src/main/java/com/wireguard/android/util/RootShell.java b/tunnel/src/main/java/com/wireguard/android/util/RootShell.java
new file mode 100644
index 00000000..1fc2c9f2
--- /dev/null
+++ b/tunnel/src/main/java/com/wireguard/android/util/RootShell.java
@@ -0,0 +1,211 @@
+/*
+ * Copyright © 2017-2019 WireGuard LLC. All Rights Reserved.
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package com.wireguard.android.util;
+
+import android.content.Context;
+import androidx.annotation.Nullable;
+import android.util.Log;
+
+import com.wireguard.android.util.RootShell.RootShellException.Reason;
+
+import java.io.BufferedReader;
+import java.io.File;
+import java.io.IOException;
+import java.io.InputStreamReader;
+import java.io.OutputStreamWriter;
+import java.nio.charset.StandardCharsets;
+import java.util.Collection;
+import java.util.UUID;
+
+/**
+ * Helper class for running commands as root.
+ */
+
+public class RootShell {
+    private static final String SU = "su";
+    private static final String TAG = "WireGuard/" + RootShell.class.getSimpleName();
+
+    private final File localBinaryDir;
+    private final File localTemporaryDir;
+    private final Object lock = new Object();
+    private final String preamble;
+    @Nullable private Process process;
+    @Nullable private BufferedReader stderr;
+    @Nullable private OutputStreamWriter stdin;
+    @Nullable private BufferedReader stdout;
+
+    public RootShell(final Context context) {
+        localBinaryDir = new File(context.getCodeCacheDir(), "bin");
+        localTemporaryDir = new File(context.getCacheDir(), "tmp");
+        preamble = String.format("export CALLING_PACKAGE=%s PATH=\"%s:$PATH\" TMPDIR='%s'; id -u\n",
+                context.getPackageName(), localBinaryDir, localTemporaryDir);
+    }
+
+    private static boolean isExecutableInPath(final String name) {
+        final String path = System.getenv("PATH");
+        if (path == null)
+            return false;
+        for (final String dir : path.split(":"))
+            if (new File(dir, name).canExecute())
+                return true;
+        return false;
+    }
+
+    private boolean isRunning() {
+        synchronized (lock) {
+            try {
+                // Throws an exception if the process hasn't finished yet.
+                if (process != null)
+                    process.exitValue();
+                return false;
+            } catch (final IllegalThreadStateException ignored) {
+                // The existing process is still running.
+                return true;
+            }
+        }
+    }
+
+    /**
+     * Run a command in a root shell.
+     *
+     * @param output  Lines read from stdout are appended to this list. Pass null if the
+     *                output from the shell is not important.
+     * @param command Command to run as root.
+     * @return The exit value of the command.
+     */
+    public int run(@Nullable final Collection<String> output, final String command)
+            throws IOException, RootShellException {
+        synchronized (lock) {
+            /* Start inside synchronized block to prevent a concurrent call to stop(). */
+            start();
+            final String marker = UUID.randomUUID().toString();
+            final String script = "echo " + marker + "; echo " + marker + " >&2; (" + command +
+                    "); ret=$?; echo " + marker + " $ret; echo " + marker + " $ret >&2\n";
+            Log.v(TAG, "executing: " + command);
+            stdin.write(script);
+            stdin.flush();
+            String line;
+            int errnoStdout = Integer.MIN_VALUE;
+            int errnoStderr = Integer.MAX_VALUE;
+            int markersSeen = 0;
+            while ((line = stdout.readLine()) != null) {
+                if (line.startsWith(marker)) {
+                    ++markersSeen;
+                    if (line.length() > marker.length() + 1) {
+                        errnoStdout = Integer.valueOf(line.substring(marker.length() + 1));
+                        break;
+                    }
+                } else if (markersSeen > 0) {
+                    if (output != null)
+                        output.add(line);
+                    Log.v(TAG, "stdout: " + line);
+                }
+            }
+            while ((line = stderr.readLine()) != null) {
+                if (line.startsWith(marker)) {
+                    ++markersSeen;
+                    if (line.length() > marker.length() + 1) {
+                        errnoStderr = Integer.valueOf(line.substring(marker.length() + 1));
+                        break;
+                    }
+                } else if (markersSeen > 2) {
+                    Log.v(TAG, "stderr: " + line);
+                }
+            }
+            if (markersSeen != 4)
+                throw new RootShellException(Reason.SHELL_MARKER_COUNT_ERROR, markersSeen);
+            if (errnoStdout != errnoStderr)
+                throw new RootShellException(Reason.SHELL_EXIT_STATUS_READ_ERROR);
+            Log.v(TAG, "exit: " + errnoStdout);
+            return errnoStdout;
+        }
+    }
+
+    public void start() throws IOException, RootShellException {
+        if (!isExecutableInPath(SU))
+            throw new RootShellException(Reason.NO_ROOT_ACCESS);
+        synchronized (lock) {
+            if (isRunning())
+                return;
+            if (!localBinaryDir.isDirectory() && !localBinaryDir.mkdirs())
+                throw new RootShellException(Reason.CREATE_BIN_DIR_ERROR);
+            if (!localTemporaryDir.isDirectory() && !localTemporaryDir.mkdirs())
+                throw new RootShellException(Reason.CREATE_TEMP_DIR_ERROR);
+            try {
+                final ProcessBuilder builder = new ProcessBuilder().command(SU);
+                builder.environment().put("LC_ALL", "C");
+                try {
+                    process = builder.start();
+                } catch (final IOException e) {
+                    // A failure at this stage means the device isn't rooted.
+                    final RootShellException rse = new RootShellException(Reason.NO_ROOT_ACCESS);
+                    rse.initCause(e);
+                    throw rse;
+                }
+                stdin = new OutputStreamWriter(process.getOutputStream(), StandardCharsets.UTF_8);
+                stdout = new BufferedReader(new InputStreamReader(process.getInputStream(),
+                        StandardCharsets.UTF_8));
+                stderr = new BufferedReader(new InputStreamReader(process.getErrorStream(),
+                        StandardCharsets.UTF_8));
+                stdin.write(preamble);
+                stdin.flush();
+                // Check that the shell started successfully.
+                final String uid = stdout.readLine();
+                if (!"0".equals(uid)) {
+                    Log.w(TAG, "Root check did not return correct UID: " + uid);
+                    throw new RootShellException(Reason.NO_ROOT_ACCESS);
+                }
+                if (!isRunning()) {
+                    String line;
+                    while ((line = stderr.readLine()) != null) {
+                        Log.w(TAG, "Root check returned an error: " + line);
+                        if (line.contains("Permission denied"))
+                            throw new RootShellException(Reason.NO_ROOT_ACCESS);
+                    }
+                    throw new RootShellException(Reason.SHELL_START_ERROR, process.exitValue());
+                }
+            } catch (final IOException | RootShellException e) {
+                stop();
+                throw e;
+            }
+        }
+    }
+
+    public void stop() {
+        synchronized (lock) {
+            if (process != null) {
+                process.destroy();
+                process = null;
+            }
+        }
+    }
+
+    public static class RootShellException extends Exception {
+        public enum Reason {
+            NO_ROOT_ACCESS,
+            SHELL_MARKER_COUNT_ERROR,
+            SHELL_EXIT_STATUS_READ_ERROR,
+            SHELL_START_ERROR,
+            CREATE_BIN_DIR_ERROR,
+            CREATE_TEMP_DIR_ERROR
+        }
+        private final Reason reason;
+        private final Object[] format;
+        public RootShellException(final Reason reason, final Object ...format) {
+            this.reason = reason;
+            this.format = format;
+        }
+        public boolean isIORelated() {
+            return reason != Reason.NO_ROOT_ACCESS;
+        }
+        public Reason getReason() {
+            return reason;
+        }
+        public Object[] getFormat() {
+            return format;
+        }
+    }
+}
diff --git a/tunnel/src/main/java/com/wireguard/android/util/SharedLibraryLoader.java b/tunnel/src/main/java/com/wireguard/android/util/SharedLibraryLoader.java
new file mode 100644
index 00000000..93e44b64
--- /dev/null
+++ b/tunnel/src/main/java/com/wireguard/android/util/SharedLibraryLoader.java
@@ -0,0 +1,94 @@
+/*
+ * Copyright © 2017-2019 WireGuard LLC. All Rights Reserved.
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package com.wireguard.android.util;
+
+import android.content.Context;
+import android.os.Build;
+import android.util.Log;
+
+import java.io.File;
+import java.io.FileOutputStream;
+import java.io.IOException;
+import java.io.InputStream;
+import java.util.Arrays;
+import java.util.Collection;
+import java.util.HashSet;
+import java.util.zip.ZipEntry;
+import java.util.zip.ZipFile;
+
+public final class SharedLibraryLoader {
+    private static final String TAG = "WireGuard/" + SharedLibraryLoader.class.getSimpleName();
+
+    private SharedLibraryLoader() {
+    }
+
+    public static boolean extractLibrary(final Context context, final String libName, final File destination) throws IOException {
+        final Collection<String> apks = new HashSet<>();
+        if (context.getApplicationInfo().sourceDir != null)
+            apks.add(context.getApplicationInfo().sourceDir);
+        if (context.getApplicationInfo().splitSourceDirs != null)
+            apks.addAll(Arrays.asList(context.getApplicationInfo().splitSourceDirs));
+
+        for (final String abi : Build.SUPPORTED_ABIS) {
+            for (final String apk : apks) {
+                final ZipFile zipFile;
+                try {
+                    zipFile = new ZipFile(new File(apk), ZipFile.OPEN_READ);
+                } catch (final IOException e) {
+                    throw new RuntimeException(e);
+                }
+
+                final String mappedLibName = System.mapLibraryName(libName);
+                final byte[] buffer = new byte[1024 * 32];
+                final String libZipPath = "lib" + File.separatorChar + abi + File.separatorChar + mappedLibName;
+                final ZipEntry zipEntry = zipFile.getEntry(libZipPath);
+                if (zipEntry == null)
+                    continue;
+                Log.d(TAG, "Extracting apk:/" + libZipPath + " to " + destination.getAbsolutePath());
+                try (final FileOutputStream out = new FileOutputStream(destination);
+                     final InputStream in = zipFile.getInputStream(zipEntry)) {
+                    int len;
+                    while ((len = in.read(buffer)) != -1) {
+                        out.write(buffer, 0, len);
+                    }
+                    out.getFD().sync();
+                }
+                zipFile.close();
+                return true;
+            }
+        }
+        return false;
+    }
+
+    public static void loadSharedLibrary(final Context context, final String libName) {
+        Throwable noAbiException;
+        try {
+            System.loadLibrary(libName);
+            return;
+        } catch (final UnsatisfiedLinkError e) {
+            Log.d(TAG, "Failed to load library normally, so attempting to extract from apk", e);
+            noAbiException = e;
+        }
+        File f = null;
+        try {
+            f = File.createTempFile("lib", ".so", context.getCodeCacheDir());
+            if (extractLibrary(context, libName, f)) {
+                System.load(f.getAbsolutePath());
+                return;
+            }
+        } catch (final Exception e) {
+            Log.d(TAG, "Failed to load library apk:/" + libName, e);
+            noAbiException = e;
+        } finally {
+            if (f != null)
+                // noinspection ResultOfMethodCallIgnored
+                f.delete();
+        }
+        if (noAbiException instanceof RuntimeException)
+            throw (RuntimeException) noAbiException;
+        throw new RuntimeException(noAbiException);
+    }
+}
diff --git a/tunnel/src/main/java/com/wireguard/android/util/ToolsInstaller.java b/tunnel/src/main/java/com/wireguard/android/util/ToolsInstaller.java
new file mode 100644
index 00000000..ac18cabf
--- /dev/null
+++ b/tunnel/src/main/java/com/wireguard/android/util/ToolsInstaller.java
@@ -0,0 +1,196 @@
+/*
+ * Copyright © 2017-2019 WireGuard LLC. All Rights Reserved.
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package com.wireguard.android.util;
+
+import android.content.Context;
+import androidx.annotation.Nullable;
+import android.system.OsConstants;
+import android.util.Log;
+
+import com.wireguard.android.util.RootShell.RootShellException;
+
+import java.io.File;
+import java.io.FileNotFoundException;
+import java.io.IOException;
+import java.util.Arrays;
+import java.util.List;
+
+/**
+ * Helper to install WireGuard tools to the system partition.
+ */
+
+public final class ToolsInstaller {
+    public static final int ERROR = 0x0;
+    public static final int MAGISK = 0x4;
+    public static final int NO = 0x2;
+    public static final int SYSTEM = 0x8;
+    public static final int YES = 0x1;
+    private static final String[] EXECUTABLES = {"wg", "wg-quick"};
+    private static final File[] INSTALL_DIRS = {
+            new File("/system/xbin"),
+            new File("/system/bin"),
+    };
+    @Nullable private static final File INSTALL_DIR = getInstallDir();
+    private static final String TAG = "WireGuard/" + ToolsInstaller.class.getSimpleName();
+
+    private final Context context;
+    private final RootShell rootShell;
+    private final File localBinaryDir;
+    private final Object lock = new Object();
+    @Nullable private Boolean areToolsAvailable;
+    @Nullable private Boolean installAsMagiskModule;
+
+    public ToolsInstaller(final Context context, final RootShell rootShell) {
+        localBinaryDir = new File(context.getCodeCacheDir(), "bin");
+        this.context = context;
+        this.rootShell = rootShell;
+    }
+
+    @Nullable
+    private static File getInstallDir() {
+        final String path = System.getenv("PATH");
+        if (path == null)
+            return INSTALL_DIRS[0];
+        final List<String> paths = Arrays.asList(path.split(":"));
+        for (final File dir : INSTALL_DIRS) {
+            if (paths.contains(dir.getPath()) && dir.isDirectory())
+                return dir;
+        }
+        return null;
+    }
+
+    public int areInstalled() throws RootShellException {
+        if (INSTALL_DIR == null)
+            return ERROR;
+        final StringBuilder script = new StringBuilder();
+        for (final String name : EXECUTABLES) {
+            script.append(String.format("cmp -s '%s' '%s' && ",
+                    new File(localBinaryDir, name).getAbsolutePath(),
+                    new File(INSTALL_DIR, name).getAbsolutePath()));
+        }
+        script.append("exit ").append(OsConstants.EALREADY).append(';');
+        try {
+            final int ret = rootShell.run(null, script.toString());
+            if (ret == OsConstants.EALREADY)
+                return willInstallAsMagiskModule() ? YES | MAGISK : YES | SYSTEM;
+            else
+                return willInstallAsMagiskModule() ? NO | MAGISK : NO | SYSTEM;
+        } catch (final IOException ignored) {
+            return ERROR;
+        } catch (final RootShellException e) {
+            if (e.isIORelated())
+                return ERROR;
+            throw e;
+        }
+    }
+
+    public void ensureToolsAvailable() throws FileNotFoundException {
+        synchronized (lock) {
+            if (areToolsAvailable == null) {
+                try {
+                    Log.d(TAG, extract() ? "Tools are now extracted into our private binary dir" :
+                            "Tools were already extracted into our private binary dir");
+                    areToolsAvailable = true;
+                } catch (final IOException e) {
+                    Log.e(TAG, "The wg and wg-quick tools are not available", e);
+                    areToolsAvailable = false;
+                }
+            }
+            if (!areToolsAvailable)
+                throw new FileNotFoundException("Required tools unavailable");
+        }
+    }
+
+    public int install() throws RootShellException, IOException {
+        if (!context.getPackageName().startsWith("com.wireguard."))
+            throw new SecurityException("The tools may only be installed system-wide from the main WireGuard app.");
+        return willInstallAsMagiskModule() ? installMagisk() : installSystem();
+    }
+
+    private int installMagisk() throws RootShellException, IOException {
+        extract();
+        final StringBuilder script = new StringBuilder("set -ex; ");
+
+        script.append("trap 'rm -rf /sbin/.magisk/img/wireguard' INT TERM EXIT; ");
+        script.append(String.format("rm -rf /sbin/.magisk/img/wireguard/; mkdir -p /sbin/.magisk/img/wireguard%s; ", INSTALL_DIR));
+        script.append("printf 'name=WireGuard Command Line Tools\nversion=1.0\nversionCode=1\nauthor=zx2c4\ndescription=Command line tools for WireGuard\nminMagisk=1500\n' > /sbin/.magisk/img/wireguard/module.prop; ");
+        script.append("touch /sbin/.magisk/img/wireguard/auto_mount; ");
+        for (final String name : EXECUTABLES) {
+            final File destination = new File("/sbin/.magisk/img/wireguard" + INSTALL_DIR, name);
+            script.append(String.format("cp '%s' '%s'; chmod 755 '%s'; chcon 'u:object_r:system_file:s0' '%s' || true; ",
+                    new File(localBinaryDir, name), destination, destination, destination));
+        }
+        script.append("trap - INT TERM EXIT;");
+
+        try {
+            return rootShell.run(null, script.toString()) == 0 ? YES | MAGISK : ERROR;
+        } catch (final IOException ignored) {
+            return ERROR;
+        } catch (final RootShellException e) {
+            if (e.isIORelated())
+                return ERROR;
+            throw e;
+        }
+    }
+
+    private int installSystem() throws RootShellException, IOException {
+        if (INSTALL_DIR == null)
+            return OsConstants.ENOENT;
+        extract();
+        final StringBuilder script = new StringBuilder("set -ex; ");
+        script.append("trap 'mount -o ro,remount /system' EXIT; mount -o rw,remount /system; ");
+        for (final String name : EXECUTABLES) {
+            final File destination = new File(INSTALL_DIR, name);
+            script.append(String.format("cp '%s' '%s'; chmod 755 '%s'; restorecon '%s' || true; ",
+                    new File(localBinaryDir, name), destination, destination, destination));
+        }
+        try {
+            return rootShell.run(null, script.toString()) == 0 ? YES | SYSTEM : ERROR;
+        } catch (final IOException ignored) {
+            return ERROR;
+        } catch (final RootShellException e) {
+            if (e.isIORelated())
+                return ERROR;
+            throw e;
+        }
+    }
+
+    public boolean extract() throws IOException {
+        localBinaryDir.mkdirs();
+        final File files[] = new File[EXECUTABLES.length];
+        final File tempFiles[] = new File[EXECUTABLES.length];
+        boolean allExist = true;
+        for (int i = 0; i < files.length; ++i) {
+            files[i] = new File(localBinaryDir, EXECUTABLES[i]);
+            tempFiles[i] = new File(localBinaryDir, EXECUTABLES[i] + ".tmp");
+            allExist &= files[i].exists();
+        }
+        if (allExist)
+            return false;
+        for (int i = 0; i < files.length; ++i) {
+            if (!SharedLibraryLoader.extractLibrary(context, EXECUTABLES[i], tempFiles[i]))
+                throw new FileNotFoundException("Unable to find " + EXECUTABLES[i]);
+            if (!tempFiles[i].setExecutable(true, false))
+                throw new IOException("Unable to mark " + tempFiles[i].getAbsolutePath() + " as executable");
+            if (!tempFiles[i].renameTo(files[i]))
+                throw new IOException("Unable to rename " + tempFiles[i].getAbsolutePath() + " to " + files[i].getAbsolutePath());
+        }
+        return true;
+    }
+
+    private boolean willInstallAsMagiskModule() {
+        synchronized (lock) {
+            if (installAsMagiskModule == null) {
+                try {
+                    installAsMagiskModule = rootShell.run(null, "[ -d /sbin/.magisk/mirror -a -d /sbin/.magisk/img -a ! -f /cache/.disable_magisk ]") == OsConstants.EXIT_SUCCESS;
+                } catch (final Exception ignored) {
+                    installAsMagiskModule = false;
+                }
+            }
+            return installAsMagiskModule;
+        }
+    }
+}
diff --git a/tunnel/src/main/java/com/wireguard/config/Attribute.java b/tunnel/src/main/java/com/wireguard/config/Attribute.java
new file mode 100644
index 00000000..1e9e25f0
--- /dev/null
+++ b/tunnel/src/main/java/com/wireguard/config/Attribute.java
@@ -0,0 +1,58 @@
+/*
+ * Copyright © 2018-2019 WireGuard LLC. All Rights Reserved.
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package com.wireguard.config;
+
+import java.util.Iterator;
+import java.util.regex.Matcher;
+import java.util.regex.Pattern;
+
+import java9.util.Optional;
+
+public final class Attribute {
+    private static final Pattern LINE_PATTERN = Pattern.compile("(\\w+)\\s*=\\s*([^\\s#][^#]*)");
+    private static final Pattern LIST_SEPARATOR = Pattern.compile("\\s*,\\s*");
+
+    private final String key;
+    private final String value;
+
+    private Attribute(final String key, final String value) {
+        this.key = key;
+        this.value = value;
+    }
+
+    public static String join(final Iterable<?> values) {
+        final Iterator<?> it = values.iterator();
+        if (!it.hasNext()) {
+            return "";
+        }
+        final StringBuilder sb = new StringBuilder();
+        sb.append(it.next());
+        while (it.hasNext()) {
+            sb.append(", ");
+            sb.append(it.next());
+        }
+        return sb.toString();
+    }
+
+    public static Optional<Attribute> parse(final CharSequence line) {
+        final Matcher matcher = LINE_PATTERN.matcher(line);
+        if (!matcher.matches())
+            return Optional.empty();
+        return Optional.of(new Attribute(matcher.group(1), matcher.group(2)));
+    }
+
+    public static String[] split(final CharSequence value) {
+        return LIST_SEPARATOR.split(value);
+    }
+
+    public String getKey() {
+        return key;
+    }
+
+    public String getValue() {
+        return value;
+    }
+}
diff --git a/tunnel/src/main/java/com/wireguard/config/BadConfigException.java b/tunnel/src/main/java/com/wireguard/config/BadConfigException.java
new file mode 100644
index 00000000..6d41b065
--- /dev/null
+++ b/tunnel/src/main/java/com/wireguard/config/BadConfigException.java
@@ -0,0 +1,118 @@
+/*
+ * Copyright © 2018-2019 WireGuard LLC. All Rights Reserved.
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package com.wireguard.config;
+
+import androidx.annotation.Nullable;
+
+import com.wireguard.crypto.KeyFormatException;
+
+public class BadConfigException extends Exception {
+    private final Location location;
+    private final Reason reason;
+    private final Section section;
+    @Nullable private final CharSequence text;
+
+    private BadConfigException(final Section section, final Location location,
+                               final Reason reason, @Nullable final CharSequence text,
+                               @Nullable final Throwable cause) {
+        super(cause);
+        this.section = section;
+        this.location = location;
+        this.reason = reason;
+        this.text = text;
+    }
+
+    public BadConfigException(final Section section, final Location location,
+                              final Reason reason, @Nullable final CharSequence text) {
+        this(section, location, reason, text, null);
+    }
+
+    public BadConfigException(final Section section, final Location location,
+                              final KeyFormatException cause) {
+        this(section, location, Reason.INVALID_KEY, null, cause);
+    }
+
+    public BadConfigException(final Section section, final Location location,
+                              @Nullable final CharSequence text,
+                              final NumberFormatException cause) {
+        this(section, location, Reason.INVALID_NUMBER, text, cause);
+    }
+
+    public BadConfigException(final Section section, final Location location,
+                              final ParseException cause) {
+        this(section, location, Reason.INVALID_VALUE, cause.getText(), cause);
+    }
+
+    public Location getLocation() {
+        return location;
+    }
+
+    public Reason getReason() {
+        return reason;
+    }
+
+    public Section getSection() {
+        return section;
+    }
+
+    @Nullable
+    public CharSequence getText() {
+        return text;
+    }
+
+    public enum Location {
+        TOP_LEVEL(""),
+        ADDRESS("Address"),
+        ALLOWED_IPS("AllowedIPs"),
+        DNS("DNS"),
+        ENDPOINT("Endpoint"),
+        EXCLUDED_APPLICATIONS("ExcludedApplications"),
+        LISTEN_PORT("ListenPort"),
+        MTU("MTU"),
+        PERSISTENT_KEEPALIVE("PersistentKeepalive"),
+        PRE_SHARED_KEY("PresharedKey"),
+        PRIVATE_KEY("PrivateKey"),
+        PUBLIC_KEY("PublicKey");
+
+        private final String name;
+
+        Location(final String name) {
+            this.name = name;
+        }
+
+        public String getName() {
+            return name;
+        }
+    }
+
+    public enum Reason {
+        INVALID_KEY,
+        INVALID_NUMBER,
+        INVALID_VALUE,
+        MISSING_ATTRIBUTE,
+        MISSING_SECTION,
+        MISSING_VALUE,
+        SYNTAX_ERROR,
+        UNKNOWN_ATTRIBUTE,
+        UNKNOWN_SECTION
+    }
+
+    public enum Section {
+        CONFIG("Config"),
+        INTERFACE("Interface"),
+        PEER("Peer");
+
+        private final String name;
+
+        Section(final String name) {
+            this.name = name;
+        }
+
+        public String getName() {
+            return name;
+        }
+    }
+}
diff --git a/tunnel/src/main/java/com/wireguard/config/Config.java b/tunnel/src/main/java/com/wireguard/config/Config.java
new file mode 100644
index 00000000..62651b08
--- /dev/null
+++ b/tunnel/src/main/java/com/wireguard/config/Config.java
@@ -0,0 +1,221 @@
+/*
+ * Copyright © 2017-2019 WireGuard LLC. All Rights Reserved.
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package com.wireguard.config;
+
+import androidx.annotation.Nullable;
+
+import com.wireguard.config.BadConfigException.Location;
+import com.wireguard.config.BadConfigException.Reason;
+import com.wireguard.config.BadConfigException.Section;
+
+import java.io.BufferedReader;
+import java.io.IOException;
+import java.io.InputStream;
+import java.io.InputStreamReader;
+import java.util.ArrayList;
+import java.util.Collection;
+import java.util.Collections;
+import java.util.LinkedHashSet;
+import java.util.List;
+import java.util.Objects;
+import java.util.Set;
+
+/**
+ * Represents the contents of a wg-quick configuration file, made up of one or more "Interface"
+ * sections (combined together), and zero or more "Peer" sections (treated individually).
+ * <p>
+ * Instances of this class are immutable.
+ */
+public final class Config {
+    private final Interface interfaze;
+    private final List<Peer> peers;
+
+    private Config(final Builder builder) {
+        interfaze = Objects.requireNonNull(builder.interfaze, "An [Interface] section is required");
+        // Defensively copy to ensure immutability even if the Builder is reused.
+        peers = Collections.unmodifiableList(new ArrayList<>(builder.peers));
+    }
+
+    /**
+     * Parses an series of "Interface" and "Peer" sections into a {@code Config}. Throws
+     * {@link BadConfigException} if the input is not well-formed or contains data that cannot
+     * be parsed.
+     *
+     * @param stream a stream of UTF-8 text that is interpreted as a WireGuard configuration
+     * @return a {@code Config} instance representing the supplied configuration
+     */
+    public static Config parse(final InputStream stream)
+            throws IOException, BadConfigException {
+        return parse(new BufferedReader(new InputStreamReader(stream)));
+    }
+
+    /**
+     * Parses an series of "Interface" and "Peer" sections into a {@code Config}. Throws
+     * {@link BadConfigException} if the input is not well-formed or contains data that cannot
+     * be parsed.
+     *
+     * @param reader a BufferedReader of UTF-8 text that is interpreted as a WireGuard configuration
+     * @return a {@code Config} instance representing the supplied configuration
+     */
+    public static Config parse(final BufferedReader reader)
+            throws IOException, BadConfigException {
+        final Builder builder = new Builder();
+        final Collection<String> interfaceLines = new ArrayList<>();
+        final Collection<String> peerLines = new ArrayList<>();
+        boolean inInterfaceSection = false;
+        boolean inPeerSection = false;
+        @Nullable String line;
+        while ((line = reader.readLine()) != null) {
+            final int commentIndex = line.indexOf('#');
+            if (commentIndex != -1)
+                line = line.substring(0, commentIndex);
+            line = line.trim();
+            if (line.isEmpty())
+                continue;
+            if (line.startsWith("[")) {
+                // Consume all [Peer] lines read so far.
+                if (inPeerSection) {
+                    builder.parsePeer(peerLines);
+                    peerLines.clear();
+                }
+                if ("[Interface]".equalsIgnoreCase(line)) {
+                    inInterfaceSection = true;
+                    inPeerSection = false;
+                } else if ("[Peer]".equalsIgnoreCase(line)) {
+                    inInterfaceSection = false;
+                    inPeerSection = true;
+                } else {
+                    throw new BadConfigException(Section.CONFIG, Location.TOP_LEVEL,
+                            Reason.UNKNOWN_SECTION, line);
+                }
+            } else if (inInterfaceSection) {
+                interfaceLines.add(line);
+            } else if (inPeerSection) {
+                peerLines.add(line);
+            } else {
+                throw new BadConfigException(Section.CONFIG, Location.TOP_LEVEL,
+                        Reason.UNKNOWN_SECTION, line);
+            }
+        }
+        if (inPeerSection)
+            builder.parsePeer(peerLines);
+        else if (!inInterfaceSection)
+            throw new BadConfigException(Section.CONFIG, Location.TOP_LEVEL,
+                    Reason.MISSING_SECTION, null);
+        // Combine all [Interface] sections in the file.
+        builder.parseInterface(interfaceLines);
+        return builder.build();
+    }
+
+    @Override
+    public boolean equals(final Object obj) {
+        if (!(obj instanceof Config))
+            return false;
+        final Config other = (Config) obj;
+        return interfaze.equals(other.interfaze) && peers.equals(other.peers);
+    }
+
+    /**
+     * Returns the interface section of the configuration.
+     *
+     * @return the interface configuration
+     */
+    public Interface getInterface() {
+        return interfaze;
+    }
+
+    /**
+     * Returns a list of the configuration's peer sections.
+     *
+     * @return a list of {@link Peer}s
+     */
+    public List<Peer> getPeers() {
+        return peers;
+    }
+
+    @Override
+    public int hashCode() {
+        return 31 * interfaze.hashCode() + peers.hashCode();
+    }
+
+    /**
+     * Converts the {@code Config} into a string suitable for debugging purposes. The {@code Config}
+     * is identified by its interface's public key and the number of peers it has.
+     *
+     * @return a concise single-line identifier for the {@code Config}
+     */
+    @Override
+    public String toString() {
+        return "(Config " + interfaze + " (" + peers.size() + " peers))";
+    }
+
+    /**
+     * Converts the {@code Config} into a string suitable for use as a {@code wg-quick}
+     * configuration file.
+     *
+     * @return the {@code Config} represented as one [Interface] and zero or more [Peer] sections
+     */
+    public String toWgQuickString() {
+        final StringBuilder sb = new StringBuilder();
+        sb.append("[Interface]\n").append(interfaze.toWgQuickString());
+        for (final Peer peer : peers)
+            sb.append("\n[Peer]\n").append(peer.toWgQuickString());
+        return sb.toString();
+    }
+
+    /**
+     * Serializes the {@code Config} for use with the WireGuard cross-platform userspace API.
+     *
+     * @return the {@code Config} represented as a series of "key=value" lines
+     */
+    public String toWgUserspaceString() {
+        final StringBuilder sb = new StringBuilder();
+        sb.append(interfaze.toWgUserspaceString());
+        sb.append("replace_peers=true\n");
+        for (final Peer peer : peers)
+            sb.append(peer.toWgUserspaceString());
+        return sb.toString();
+    }
+
+    @SuppressWarnings("UnusedReturnValue")
+    public static final class Builder {
+        // Defaults to an empty set.
+        private final Set<Peer> peers = new LinkedHashSet<>();
+        // No default; must be provided before building.
+        @Nullable private Interface interfaze;
+
+        public Builder addPeer(final Peer peer) {
+            peers.add(peer);
+            return this;
+        }
+
+        public Builder addPeers(final Collection<Peer> peers) {
+            this.peers.addAll(peers);
+            return this;
+        }
+
+        public Config build() {
+            if (interfaze == null)
+                throw new IllegalArgumentException("An [Interface] section is required");
+            return new Config(this);
+        }
+
+        public Builder parseInterface(final Iterable<? extends CharSequence> lines)
+                throws BadConfigException {
+            return setInterface(Interface.parse(lines));
+        }
+
+        public Builder parsePeer(final Iterable<? extends CharSequence> lines)
+                throws BadConfigException {
+            return addPeer(Peer.parse(lines));
+        }
+
+        public Builder setInterface(final Interface interfaze) {
+            this.interfaze = interfaze;
+            return this;
+        }
+    }
+}
diff --git a/tunnel/src/main/java/com/wireguard/config/InetAddresses.java b/tunnel/src/main/java/com/wireguard/config/InetAddresses.java
new file mode 100644
index 00000000..5303e27f
--- /dev/null
+++ b/tunnel/src/main/java/com/wireguard/config/InetAddresses.java
@@ -0,0 +1,71 @@
+/*
+ * Copyright © 2017-2019 WireGuard LLC. All Rights Reserved.
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package com.wireguard.config;
+
+import java.lang.reflect.Method;
+import java.net.Inet4Address;
+import java.net.Inet6Address;
+import java.net.InetAddress;
+import java.net.UnknownHostException;
+import java.util.regex.Pattern;
+
+import javax.annotation.Nullable;
+
+/**
+ * Utility methods for creating instances of {@link InetAddress}.
+ */
+public final class InetAddresses {
+    @Nullable private static final Method PARSER_METHOD;
+    private static final Pattern WONT_TOUCH_RESOLVER = Pattern.compile("^(((([0-9A-Fa-f]{1,4}:){7}([0-9A-Fa-f]{1,4}|:))|(([0-9A-Fa-f]{1,4}:){6}(:[0-9A-Fa-f]{1,4}|((25[0-5]|2[0-4]\\d|1\\d\\d|[1-9]?\\d)(\\.(25[0-5]|2[0-4]\\d|1\\d\\d|[1-9]?\\d)){3})|:))|(([0-9A-Fa-f]{1,4}:){5}(((:[0-9A-Fa-f]{1,4}){1,2})|:((25[0-5]|2[0-4]\\d|1\\d\\d|[1-9]?\\d)(\\.(25[0-5]|2[0-4]\\d|1\\d\\d|[1-9]?\\d)){3})|:))|(([0-9A-Fa-f]{1,4}:){4}(((:[0-9A-Fa-f]{1,4}){1,3})|((:[0-9A-Fa-f]{1,4})?:((25[0-5]|2[0-4]\\d|1\\d\\d|[1-9]?\\d)(\\.(25[0-5]|2[0-4]\\d|1\\d\\d|[1-9]?\\d)){3}))|:))|(([0-9A-Fa-f]{1,4}:){3}(((:[0-9A-Fa-f]{1,4}){1,4})|((:[0-9A-Fa-f]{1,4}){0,2}:((25[0-5]|2[0-4]\\d|1\\d\\d|[1-9]?\\d)(\\.(25[0-5]|2[0-4]\\d|1\\d\\d|[1-9]?\\d)){3}))|:))|(([0-9A-Fa-f]{1,4}:){2}(((:[0-9A-Fa-f]{1,4}){1,5})|((:[0-9A-Fa-f]{1,4}){0,3}:((25[0-5]|2[0-4]\\d|1\\d\\d|[1-9]?\\d)(\\.(25[0-5]|2[0-4]\\d|1\\d\\d|[1-9]?\\d)){3}))|:))|(([0-9A-Fa-f]{1,4}:){1}(((:[0-9A-Fa-f]{1,4}){1,6})|((:[0-9A-Fa-f]{1,4}){0,4}:((25[0-5]|2[0-4]\\d|1\\d\\d|[1-9]?\\d)(\\.(25[0-5]|2[0-4]\\d|1\\d\\d|[1-9]?\\d)){3}))|:))|(:(((:[0-9A-Fa-f]{1,4}){1,7})|((:[0-9A-Fa-f]{1,4}){0,5}:((25[0-5]|2[0-4]\\d|1\\d\\d|[1-9]?\\d)(\\.(25[0-5]|2[0-4]\\d|1\\d\\d|[1-9]?\\d)){3}))|:)))(%.+)?)|((?:(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\\.){3}(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?))$");
+
+    static {
+        Method m = null;
+        try {
+            if (android.os.Build.VERSION.SDK_INT < android.os.Build.VERSION_CODES.Q)
+                // noinspection JavaReflectionMemberAccess
+                m = InetAddress.class.getMethod("parseNumericAddress", String.class);
+        } catch (final Exception ignored) {
+        }
+        PARSER_METHOD = m;
+    }
+
+    private InetAddresses() { }
+
+    /**
+     * Parses a numeric IPv4 or IPv6 address without performing any DNS lookups.
+     *
+     * @param address a string representing the IP address
+     * @return an instance of {@link Inet4Address} or {@link Inet6Address}, as appropriate
+     */
+    public static InetAddress parse(final String address) throws ParseException {
+        if (address.isEmpty())
+            throw new ParseException(InetAddress.class, address, "Empty address");
+        try {
+            if (android.os.Build.VERSION.SDK_INT >= android.os.Build.VERSION_CODES.Q)
+                return android.net.InetAddresses.parseNumericAddress(address);
+            else if (PARSER_METHOD != null)
+                return (InetAddress) PARSER_METHOD.invoke(null, address);
+            else
+                throw new NoSuchMethodException("parseNumericAddress");
+        } catch (final IllegalArgumentException e) {
+            throw new ParseException(InetAddress.class, address, e);
+        } catch (final Exception e) {
+            final Throwable cause = e.getCause();
+            // Re-throw parsing exceptions with the original type, as callers might try to catch
+            // them. On the other hand, callers cannot be expected to handle reflection failures.
+            if (cause instanceof IllegalArgumentException)
+                throw new ParseException(InetAddress.class, address, cause);
+            try {
+                if (WONT_TOUCH_RESOLVER.matcher(address).matches())
+                    return InetAddress.getByName(address);
+                else
+                    throw new ParseException(InetAddress.class, address, "Not an IP address");
+            } catch (final UnknownHostException f) {
+                throw new ParseException(InetAddress.class, address, f);
+            }
+        }
+    }
+}
diff --git a/tunnel/src/main/java/com/wireguard/config/InetEndpoint.java b/tunnel/src/main/java/com/wireguard/config/InetEndpoint.java
new file mode 100644
index 00000000..a442258e
--- /dev/null
+++ b/tunnel/src/main/java/com/wireguard/config/InetEndpoint.java
@@ -0,0 +1,125 @@
+/*
+ * Copyright © 2017-2019 WireGuard LLC. All Rights Reserved.
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package com.wireguard.config;
+
+import androidx.annotation.Nullable;
+
+import org.threeten.bp.Duration;
+import org.threeten.bp.Instant;
+
+import java.net.Inet4Address;
+import java.net.InetAddress;
+import java.net.URI;
+import java.net.URISyntaxException;
+import java.net.UnknownHostException;
+import java.util.regex.Pattern;
+
+import java9.util.Optional;
+
+
+/**
+ * An external endpoint (host and port) used to connect to a WireGuard {@link Peer}.
+ * <p>
+ * Instances of this class are externally immutable.
+ */
+public final class InetEndpoint {
+    private static final Pattern BARE_IPV6 = Pattern.compile("^[^\\[\\]]*:[^\\[\\]]*");
+    private static final Pattern FORBIDDEN_CHARACTERS = Pattern.compile("[/?#]");
+
+    private final String host;
+    private final boolean isResolved;
+    private final Object lock = new Object();
+    private final int port;
+    private Instant lastResolution = Instant.EPOCH;
+    @Nullable private InetEndpoint resolved;
+
+    private InetEndpoint(final String host, final boolean isResolved, final int port) {
+        this.host = host;
+        this.isResolved = isResolved;
+        this.port = port;
+    }
+
+    public static InetEndpoint parse(final String endpoint) throws ParseException {
+        if (FORBIDDEN_CHARACTERS.matcher(endpoint).find())
+            throw new ParseException(InetEndpoint.class, endpoint, "Forbidden characters");
+        final URI uri;
+        try {
+            uri = new URI("wg://" + endpoint);
+        } catch (final URISyntaxException e) {
+            throw new IllegalArgumentException(e);
+        }
+        if (uri.getPort() < 0 || uri.getPort() > 65535)
+            throw new ParseException(InetEndpoint.class, endpoint, "Missing/invalid port number");
+        try {
+            InetAddresses.parse(uri.getHost());
+            // Parsing ths host as a numeric address worked, so we don't need to do DNS lookups.
+            return new InetEndpoint(uri.getHost(), true, uri.getPort());
+        } catch (final ParseException ignored) {
+            // Failed to parse the host as a numeric address, so it must be a DNS hostname/FQDN.
+            return new InetEndpoint(uri.getHost(), false, uri.getPort());
+        }
+    }
+
+    @Override
+    public boolean equals(final Object obj) {
+        if (!(obj instanceof InetEndpoint))
+            return false;
+        final InetEndpoint other = (InetEndpoint) obj;
+        return host.equals(other.host) && port == other.port;
+    }
+
+    public String getHost() {
+        return host;
+    }
+
+    public int getPort() {
+        return port;
+    }
+
+    /**
+     * Generate an {@code InetEndpoint} instance with the same port and the host resolved using DNS
+     * to a numeric address. If the host is already numeric, the existing instance may be returned.
+     * Because this function may perform network I/O, it must not be called from the main thread.
+     *
+     * @return the resolved endpoint, or {@link Optional#empty()}
+     */
+    public Optional<InetEndpoint> getResolved() {
+        if (isResolved)
+            return Optional.of(this);
+        synchronized (lock) {
+            //TODO(zx2c4): Implement a real timeout mechanism using DNS TTL
+            if (Duration.between(lastResolution, Instant.now()).toMinutes() > 1) {
+                try {
+                    // Prefer v4 endpoints over v6 to work around DNS64 and IPv6 NAT issues.
+                    final InetAddress[] candidates = InetAddress.getAllByName(host);
+                    InetAddress address = candidates[0];
+                    for (final InetAddress candidate : candidates) {
+                        if (candidate instanceof Inet4Address) {
+                            address = candidate;
+                            break;
+                        }
+                    }
+                    resolved = new InetEndpoint(address.getHostAddress(), true, port);
+                    lastResolution = Instant.now();
+                } catch (final UnknownHostException e) {
+                    resolved = null;
+                }
+            }
+            return Optional.ofNullable(resolved);
+        }
+    }
+
+    @Override
+    public int hashCode() {
+        return host.hashCode() ^ port;
+    }
+
+    @Override
+    public String toString() {
+        final boolean isBareIpv6 = isResolved && BARE_IPV6.matcher(host).matches();
+        return (isBareIpv6 ? '[' + host + ']' : host) + ':' + port;
+    }
+}
diff --git a/tunnel/src/main/java/com/wireguard/config/InetNetwork.java b/tunnel/src/main/java/com/wireguard/config/InetNetwork.java
new file mode 100644
index 00000000..f89322fd
--- /dev/null
+++ b/tunnel/src/main/java/com/wireguard/config/InetNetwork.java
@@ -0,0 +1,76 @@
+/*
+ * Copyright © 2017-2019 WireGuard LLC. All Rights Reserved.
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package com.wireguard.config;
+
+import java.net.Inet4Address;
+import java.net.InetAddress;
+
+/**
+ * An Internet network, denoted by its address and netmask
+ * <p>
+ * Instances of this class are immutable.
+ */
+public final class InetNetwork {
+    private final InetAddress address;
+    private final int mask;
+
+    private InetNetwork(final InetAddress address, final int mask) {
+        this.address = address;
+        this.mask = mask;
+    }
+
+    public static InetNetwork parse(final String network) throws ParseException {
+        final int slash = network.lastIndexOf('/');
+        final String maskString;
+        final int rawMask;
+        final String rawAddress;
+        if (slash >= 0) {
+            maskString = network.substring(slash + 1);
+            try {
+                rawMask = Integer.parseInt(maskString, 10);
+            } catch (final NumberFormatException ignored) {
+                throw new ParseException(Integer.class, maskString);
+            }
+            rawAddress = network.substring(0, slash);
+        } else {
+            maskString = "";
+            rawMask = -1;
+            rawAddress = network;
+        }
+        final InetAddress address = InetAddresses.parse(rawAddress);
+        final int maxMask = (address instanceof Inet4Address) ? 32 : 128;
+        if (rawMask > maxMask)
+            throw new ParseException(InetNetwork.class, maskString, "Invalid network mask");
+        final int mask = rawMask >= 0 && rawMask <= maxMask ? rawMask : maxMask;
+        return new InetNetwork(address, mask);
+    }
+
+    @Override
+    public boolean equals(final Object obj) {
+        if (!(obj instanceof InetNetwork))
+            return false;
+        final InetNetwork other = (InetNetwork) obj;
+        return address.equals(other.address) && mask == other.mask;
+    }
+
+    public InetAddress getAddress() {
+        return address;
+    }
+
+    public int getMask() {
+        return mask;
+    }
+
+    @Override
+    public int hashCode() {
+        return address.hashCode() ^ mask;
+    }
+
+    @Override
+    public String toString() {
+        return address.getHostAddress() + '/' + mask;
+    }
+}
diff --git a/tunnel/src/main/java/com/wireguard/config/Interface.java b/tunnel/src/main/java/com/wireguard/config/Interface.java
new file mode 100644
index 00000000..54944424
--- /dev/null
+++ b/tunnel/src/main/java/com/wireguard/config/Interface.java
@@ -0,0 +1,355 @@
+/*
+ * Copyright © 2017-2019 WireGuard LLC. All Rights Reserved.
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package com.wireguard.config;
+
+import androidx.annotation.Nullable;
+
+import com.wireguard.config.BadConfigException.Location;
+import com.wireguard.config.BadConfigException.Reason;
+import com.wireguard.config.BadConfigException.Section;
+import com.wireguard.crypto.Key;
+import com.wireguard.crypto.KeyFormatException;
+import com.wireguard.crypto.KeyPair;
+
+import java.net.InetAddress;
+import java.util.Collection;
+import java.util.Collections;
+import java.util.LinkedHashSet;
+import java.util.List;
+import java.util.Locale;
+import java.util.Objects;
+import java.util.Set;
+
+import java9.util.Lists;
+import java9.util.Optional;
+import java9.util.stream.Collectors;
+import java9.util.stream.StreamSupport;
+
+/**
+ * Represents the configuration for a WireGuard interface (an [Interface] block). Interfaces must
+ * have a private key (used to initialize a {@code KeyPair}), and may optionally have several other
+ * attributes.
+ * <p>
+ * Instances of this class are immutable.
+ */
+public final class Interface {
+    private static final int MAX_UDP_PORT = 65535;
+    private static final int MIN_UDP_PORT = 0;
+
+    private final Set<InetNetwork> addresses;
+    private final Set<InetAddress> dnsServers;
+    private final Set<String> excludedApplications;
+    private final KeyPair keyPair;
+    private final Optional<Integer> listenPort;
+    private final Optional<Integer> mtu;
+
+    private Interface(final Builder builder) {
+        // Defensively copy to ensure immutability even if the Builder is reused.
+        addresses = Collections.unmodifiableSet(new LinkedHashSet<>(builder.addresses));
+        dnsServers = Collections.unmodifiableSet(new LinkedHashSet<>(builder.dnsServers));
+        excludedApplications = Collections.unmodifiableSet(new LinkedHashSet<>(builder.excludedApplications));
+        keyPair = Objects.requireNonNull(builder.keyPair, "Interfaces must have a private key");
+        listenPort = builder.listenPort;
+        mtu = builder.mtu;
+    }
+
+    /**
+     * Parses an series of "KEY = VALUE" lines into an {@code Interface}. Throws
+     * {@link ParseException} if the input is not well-formed or contains unknown attributes.
+     *
+     * @param lines An iterable sequence of lines, containing at least a private key attribute
+     * @return An {@code Interface} with all of the attributes from {@code lines} set
+     */
+    public static Interface parse(final Iterable<? extends CharSequence> lines)
+            throws BadConfigException {
+        final Builder builder = new Builder();
+        for (final CharSequence line : lines) {
+            final Attribute attribute = Attribute.parse(line).orElseThrow(() ->
+                    new BadConfigException(Section.INTERFACE, Location.TOP_LEVEL,
+                            Reason.SYNTAX_ERROR, line));
+            switch (attribute.getKey().toLowerCase(Locale.ENGLISH)) {
+                case "address":
+                    builder.parseAddresses(attribute.getValue());
+                    break;
+                case "dns":
+                    builder.parseDnsServers(attribute.getValue());
+                    break;
+                case "excludedapplications":
+                    builder.parseExcludedApplications(attribute.getValue());
+                    break;
+                case "listenport":
+                    builder.parseListenPort(attribute.getValue());
+                    break;
+                case "mtu":
+                    builder.parseMtu(attribute.getValue());
+                    break;
+                case "privatekey":
+                    builder.parsePrivateKey(attribute.getValue());
+                    break;
+                default:
+                    throw new BadConfigException(Section.INTERFACE, Location.TOP_LEVEL,
+                            Reason.UNKNOWN_ATTRIBUTE, attribute.getKey());
+            }
+        }
+        return builder.build();
+    }
+
+    @Override
+    public boolean equals(final Object obj) {
+        if (!(obj instanceof Interface))
+            return false;
+        final Interface other = (Interface) obj;
+        return addresses.equals(other.addresses)
+                && dnsServers.equals(other.dnsServers)
+                && excludedApplications.equals(other.excludedApplications)
+                && keyPair.equals(other.keyPair)
+                && listenPort.equals(other.listenPort)
+                && mtu.equals(other.mtu);
+    }
+
+    /**
+     * Returns the set of IP addresses assigned to the interface.
+     *
+     * @return a set of {@link InetNetwork}s
+     */
+    public Set<InetNetwork> getAddresses() {
+        // The collection is already immutable.
+        return addresses;
+    }
+
+    /**
+     * Returns the set of DNS servers associated with the interface.
+     *
+     * @return a set of {@link InetAddress}es
+     */
+    public Set<InetAddress> getDnsServers() {
+        // The collection is already immutable.
+        return dnsServers;
+    }
+
+    /**
+     * Returns the set of applications excluded from using the interface.
+     *
+     * @return a set of package names
+     */
+    public Set<String> getExcludedApplications() {
+        // The collection is already immutable.
+        return excludedApplications;
+    }
+
+    /**
+     * Returns the public/private key pair used by the interface.
+     *
+     * @return a key pair
+     */
+    public KeyPair getKeyPair() {
+        return keyPair;
+    }
+
+    /**
+     * Returns the UDP port number that the WireGuard interface will listen on.
+     *
+     * @return a UDP port number, or {@code Optional.empty()} if none is configured
+     */
+    public Optional<Integer> getListenPort() {
+        return listenPort;
+    }
+
+    /**
+     * Returns the MTU used for the WireGuard interface.
+     *
+     * @return the MTU, or {@code Optional.empty()} if none is configured
+     */
+    public Optional<Integer> getMtu() {
+        return mtu;
+    }
+
+    @Override
+    public int hashCode() {
+        int hash = 1;
+        hash = 31 * hash + addresses.hashCode();
+        hash = 31 * hash + dnsServers.hashCode();
+        hash = 31 * hash + excludedApplications.hashCode();
+        hash = 31 * hash + keyPair.hashCode();
+        hash = 31 * hash + listenPort.hashCode();
+        hash = 31 * hash + mtu.hashCode();
+        return hash;
+    }
+
+    /**
+     * Converts the {@code Interface} into a string suitable for debugging purposes. The {@code
+     * Interface} is identified by its public key and (if set) the port used for its UDP socket.
+     *
+     * @return A concise single-line identifier for the {@code Interface}
+     */
+    @Override
+    public String toString() {
+        final StringBuilder sb = new StringBuilder("(Interface ");
+        sb.append(keyPair.getPublicKey().toBase64());
+        listenPort.ifPresent(lp -> sb.append(" @").append(lp));
+        sb.append(')');
+        return sb.toString();
+    }
+
+    /**
+     * Converts the {@code Interface} into a string suitable for inclusion in a {@code wg-quick}
+     * configuration file.
+     *
+     * @return The {@code Interface} represented as a series of "Key = Value" lines
+     */
+    public String toWgQuickString() {
+        final StringBuilder sb = new StringBuilder();
+        if (!addresses.isEmpty())
+            sb.append("Address = ").append(Attribute.join(addresses)).append('\n');
+        if (!dnsServers.isEmpty()) {
+            final List<String> dnsServerStrings = StreamSupport.stream(dnsServers)
+                    .map(InetAddress::getHostAddress)
+                    .collect(Collectors.toUnmodifiableList());
+            sb.append("DNS = ").append(Attribute.join(dnsServerStrings)).append('\n');
+        }
+        if (!excludedApplications.isEmpty())
+            sb.append("ExcludedApplications = ").append(Attribute.join(excludedApplications)).append('\n');
+        listenPort.ifPresent(lp -> sb.append("ListenPort = ").append(lp).append('\n'));
+        mtu.ifPresent(m -> sb.append("MTU = ").append(m).append('\n'));
+        sb.append("PrivateKey = ").append(keyPair.getPrivateKey().toBase64()).append('\n');
+        return sb.toString();
+    }
+
+    /**
+     * Serializes the {@code Interface} for use with the WireGuard cross-platform userspace API.
+     * Note that not all attributes are included in this representation.
+     *
+     * @return the {@code Interface} represented as a series of "KEY=VALUE" lines
+     */
+    public String toWgUserspaceString() {
+        final StringBuilder sb = new StringBuilder();
+        sb.append("private_key=").append(keyPair.getPrivateKey().toHex()).append('\n');
+        listenPort.ifPresent(lp -> sb.append("listen_port=").append(lp).append('\n'));
+        return sb.toString();
+    }
+
+    @SuppressWarnings("UnusedReturnValue")
+    public static final class Builder {
+        // Defaults to an empty set.
+        private final Set<InetNetwork> addresses = new LinkedHashSet<>();
+        // Defaults to an empty set.
+        private final Set<InetAddress> dnsServers = new LinkedHashSet<>();
+        // Defaults to an empty set.
+        private final Set<String> excludedApplications = new LinkedHashSet<>();
+        // No default; must be provided before building.
+        @Nullable private KeyPair keyPair;
+        // Defaults to not present.
+        private Optional<Integer> listenPort = Optional.empty();
+        // Defaults to not present.
+        private Optional<Integer> mtu = Optional.empty();
+
+        public Builder addAddress(final InetNetwork address) {
+            addresses.add(address);
+            return this;
+        }
+
+        public Builder addAddresses(final Collection<InetNetwork> addresses) {
+            this.addresses.addAll(addresses);
+            return this;
+        }
+
+        public Builder addDnsServer(final InetAddress dnsServer) {
+            dnsServers.add(dnsServer);
+            return this;
+        }
+
+        public Builder addDnsServers(final Collection<? extends InetAddress> dnsServers) {
+            this.dnsServers.addAll(dnsServers);
+            return this;
+        }
+
+        public Interface build() throws BadConfigException {
+            if (keyPair == null)
+                throw new BadConfigException(Section.INTERFACE, Location.PRIVATE_KEY,
+                        Reason.MISSING_ATTRIBUTE, null);
+            return new Interface(this);
+        }
+
+        public Builder excludeApplication(final String application) {
+            excludedApplications.add(application);
+            return this;
+        }
+
+        public Builder excludeApplications(final Collection<String> applications) {
+            excludedApplications.addAll(applications);
+            return this;
+        }
+
+        public Builder parseAddresses(final CharSequence addresses) throws BadConfigException {
+            try {
+                for (final String address : Attribute.split(addresses))
+                    addAddress(InetNetwork.parse(address));
+                return this;
+            } catch (final ParseException e) {
+                throw new BadConfigException(Section.INTERFACE, Location.ADDRESS, e);
+            }
+        }
+
+        public Builder parseDnsServers(final CharSequence dnsServers) throws BadConfigException {
+            try {
+                for (final String dnsServer : Attribute.split(dnsServers))
+                    addDnsServer(InetAddresses.parse(dnsServer));
+                return this;
+            } catch (final ParseException e) {
+                throw new BadConfigException(Section.INTERFACE, Location.DNS, e);
+            }
+        }
+
+        public Builder parseExcludedApplications(final CharSequence apps) {
+            return excludeApplications(Lists.of(Attribute.split(apps)));
+        }
+
+        public Builder parseListenPort(final String listenPort) throws BadConfigException {
+            try {
+                return setListenPort(Integer.parseInt(listenPort));
+            } catch (final NumberFormatException e) {
+                throw new BadConfigException(Section.INTERFACE, Location.LISTEN_PORT, listenPort, e);
+            }
+        }
+
+        public Builder parseMtu(final String mtu) throws BadConfigException {
+            try {
+                return setMtu(Integer.parseInt(mtu));
+            } catch (final NumberFormatException e) {
+                throw new BadConfigException(Section.INTERFACE, Location.MTU, mtu, e);
+            }
+        }
+
+        public Builder parsePrivateKey(final String privateKey) throws BadConfigException {
+            try {
+                return setKeyPair(new KeyPair(Key.fromBase64(privateKey)));
+            } catch (final KeyFormatException e) {
+                throw new BadConfigException(Section.INTERFACE, Location.PRIVATE_KEY, e);
+            }
+        }
+
+        public Builder setKeyPair(final KeyPair keyPair) {
+            this.keyPair = keyPair;
+            return this;
+        }
+
+        public Builder setListenPort(final int listenPort) throws BadConfigException {
+            if (listenPort < MIN_UDP_PORT || listenPort > MAX_UDP_PORT)
+                throw new BadConfigException(Section.INTERFACE, Location.LISTEN_PORT,
+                        Reason.INVALID_VALUE, String.valueOf(listenPort));
+            this.listenPort = listenPort == 0 ? Optional.empty() : Optional.of(listenPort);
+            return this;
+        }
+
+        public Builder setMtu(final int mtu) throws BadConfigException {
+            if (mtu < 0)
+                throw new BadConfigException(Section.INTERFACE, Location.LISTEN_PORT,
+                        Reason.INVALID_VALUE, String.valueOf(mtu));
+            this.mtu = mtu == 0 ? Optional.empty() : Optional.of(mtu);
+            return this;
+        }
+    }
+}
diff --git a/tunnel/src/main/java/com/wireguard/config/ParseException.java b/tunnel/src/main/java/com/wireguard/config/ParseException.java
new file mode 100644
index 00000000..c79d1fa1
--- /dev/null
+++ b/tunnel/src/main/java/com/wireguard/config/ParseException.java
@@ -0,0 +1,44 @@
+/*
+ * Copyright © 2018-2019 WireGuard LLC. All Rights Reserved.
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package com.wireguard.config;
+
+import androidx.annotation.Nullable;
+
+/**
+ */
+public class ParseException extends Exception {
+    private final Class<?> parsingClass;
+    private final CharSequence text;
+
+    public ParseException(final Class<?> parsingClass, final CharSequence text,
+                          @Nullable final String message, @Nullable final Throwable cause) {
+        super(message, cause);
+        this.parsingClass = parsingClass;
+        this.text = text;
+    }
+
+    public ParseException(final Class<?> parsingClass, final CharSequence text,
+                          @Nullable final String message) {
+        this(parsingClass, text, message, null);
+    }
+
+    public ParseException(final Class<?> parsingClass, final CharSequence text,
+                          @Nullable final Throwable cause) {
+        this(parsingClass, text, null, cause);
+    }
+
+    public ParseException(final Class<?> parsingClass, final CharSequence text) {
+        this(parsingClass, text, null, null);
+    }
+
+    public Class<?> getParsingClass() {
+        return parsingClass;
+    }
+
+    public CharSequence getText() {
+        return text;
+    }
+}
diff --git a/tunnel/src/main/java/com/wireguard/config/Peer.java b/tunnel/src/main/java/com/wireguard/config/Peer.java
new file mode 100644
index 00000000..37fcfa69
--- /dev/null
+++ b/tunnel/src/main/java/com/wireguard/config/Peer.java
@@ -0,0 +1,306 @@
+/*
+ * Copyright © 2017-2019 WireGuard LLC. All Rights Reserved.
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package com.wireguard.config;
+
+import androidx.annotation.Nullable;
+
+import com.wireguard.config.BadConfigException.Location;
+import com.wireguard.config.BadConfigException.Reason;
+import com.wireguard.config.BadConfigException.Section;
+import com.wireguard.crypto.Key;
+import com.wireguard.crypto.KeyFormatException;
+
+import java.util.Collection;
+import java.util.Collections;
+import java.util.LinkedHashSet;
+import java.util.Locale;
+import java.util.Objects;
+import java.util.Set;
+
+import java9.util.Optional;
+
+/**
+ * Represents the configuration for a WireGuard peer (a [Peer] block). Peers must have a public key,
+ * and may optionally have several other attributes.
+ * <p>
+ * Instances of this class are immutable.
+ */
+public final class Peer {
+    private final Set<InetNetwork> allowedIps;
+    private final Optional<InetEndpoint> endpoint;
+    private final Optional<Integer> persistentKeepalive;
+    private final Optional<Key> preSharedKey;
+    private final Key publicKey;
+
+    private Peer(final Builder builder) {
+        // Defensively copy to ensure immutability even if the Builder is reused.
+        allowedIps = Collections.unmodifiableSet(new LinkedHashSet<>(builder.allowedIps));
+        endpoint = builder.endpoint;
+        persistentKeepalive = builder.persistentKeepalive;
+        preSharedKey = builder.preSharedKey;
+        publicKey = Objects.requireNonNull(builder.publicKey, "Peers must have a public key");
+    }
+
+    /**
+     * Parses an series of "KEY = VALUE" lines into a {@code Peer}. Throws {@link ParseException} if
+     * the input is not well-formed or contains unknown attributes.
+     *
+     * @param lines an iterable sequence of lines, containing at least a public key attribute
+     * @return a {@code Peer} with all of its attributes set from {@code lines}
+     */
+    public static Peer parse(final Iterable<? extends CharSequence> lines)
+            throws BadConfigException {
+        final Builder builder = new Builder();
+        for (final CharSequence line : lines) {
+            final Attribute attribute = Attribute.parse(line).orElseThrow(() ->
+                    new BadConfigException(Section.PEER, Location.TOP_LEVEL,
+                            Reason.SYNTAX_ERROR, line));
+            switch (attribute.getKey().toLowerCase(Locale.ENGLISH)) {
+                case "allowedips":
+                    builder.parseAllowedIPs(attribute.getValue());
+                    break;
+                case "endpoint":
+                    builder.parseEndpoint(attribute.getValue());
+                    break;
+                case "persistentkeepalive":
+                    builder.parsePersistentKeepalive(attribute.getValue());
+                    break;
+                case "presharedkey":
+                    builder.parsePreSharedKey(attribute.getValue());
+                    break;
+                case "publickey":
+                    builder.parsePublicKey(attribute.getValue());
+                    break;
+                default:
+                    throw new BadConfigException(Section.PEER, Location.TOP_LEVEL,
+                            Reason.UNKNOWN_ATTRIBUTE, attribute.getKey());
+            }
+        }
+        return builder.build();
+    }
+
+    @Override
+    public boolean equals(final Object obj) {
+        if (!(obj instanceof Peer))
+            return false;
+        final Peer other = (Peer) obj;
+        return allowedIps.equals(other.allowedIps)
+                && endpoint.equals(other.endpoint)
+                && persistentKeepalive.equals(other.persistentKeepalive)
+                && preSharedKey.equals(other.preSharedKey)
+                && publicKey.equals(other.publicKey);
+    }
+
+    /**
+     * Returns the peer's set of allowed IPs.
+     *
+     * @return the set of allowed IPs
+     */
+    public Set<InetNetwork> getAllowedIps() {
+        // The collection is already immutable.
+        return allowedIps;
+    }
+
+    /**
+     * Returns the peer's endpoint.
+     *
+     * @return the endpoint, or {@code Optional.empty()} if none is configured
+     */
+    public Optional<InetEndpoint> getEndpoint() {
+        return endpoint;
+    }
+
+    /**
+     * Returns the peer's persistent keepalive.
+     *
+     * @return the persistent keepalive, or {@code Optional.empty()} if none is configured
+     */
+    public Optional<Integer> getPersistentKeepalive() {
+        return persistentKeepalive;
+    }
+
+    /**
+     * Returns the peer's pre-shared key.
+     *
+     * @return the pre-shared key, or {@code Optional.empty()} if none is configured
+     */
+    public Optional<Key> getPreSharedKey() {
+        return preSharedKey;
+    }
+
+    /**
+     * Returns the peer's public key.
+     *
+     * @return the public key
+     */
+    public Key getPublicKey() {
+        return publicKey;
+    }
+
+    @Override
+    public int hashCode() {
+        int hash = 1;
+        hash = 31 * hash + allowedIps.hashCode();
+        hash = 31 * hash + endpoint.hashCode();
+        hash = 31 * hash + persistentKeepalive.hashCode();
+        hash = 31 * hash + preSharedKey.hashCode();
+        hash = 31 * hash + publicKey.hashCode();
+        return hash;
+    }
+
+    /**
+     * Converts the {@code Peer} into a string suitable for debugging purposes. The {@code Peer} is
+     * identified by its public key and (if known) its endpoint.
+     *
+     * @return a concise single-line identifier for the {@code Peer}
+     */
+    @Override
+    public String toString() {
+        final StringBuilder sb = new StringBuilder("(Peer ");
+        sb.append(publicKey.toBase64());
+        endpoint.ifPresent(ep -> sb.append(" @").append(ep));
+        sb.append(')');
+        return sb.toString();
+    }
+
+    /**
+     * Converts the {@code Peer} into a string suitable for inclusion in a {@code wg-quick}
+     * configuration file.
+     *
+     * @return the {@code Peer} represented as a series of "Key = Value" lines
+     */
+    public String toWgQuickString() {
+        final StringBuilder sb = new StringBuilder();
+        if (!allowedIps.isEmpty())
+            sb.append("AllowedIPs = ").append(Attribute.join(allowedIps)).append('\n');
+        endpoint.ifPresent(ep -> sb.append("Endpoint = ").append(ep).append('\n'));
+        persistentKeepalive.ifPresent(pk -> sb.append("PersistentKeepalive = ").append(pk).append('\n'));
+        preSharedKey.ifPresent(psk -> sb.append("PreSharedKey = ").append(psk.toBase64()).append('\n'));
+        sb.append("PublicKey = ").append(publicKey.toBase64()).append('\n');
+        return sb.toString();
+    }
+
+    /**
+     * Serializes the {@code Peer} for use with the WireGuard cross-platform userspace API. Note
+     * that not all attributes are included in this representation.
+     *
+     * @return the {@code Peer} represented as a series of "key=value" lines
+     */
+    public String toWgUserspaceString() {
+        final StringBuilder sb = new StringBuilder();
+        // The order here is important: public_key signifies the beginning of a new peer.
+        sb.append("public_key=").append(publicKey.toHex()).append('\n');
+        for (final InetNetwork allowedIp : allowedIps)
+            sb.append("allowed_ip=").append(allowedIp).append('\n');
+        endpoint.flatMap(InetEndpoint::getResolved).ifPresent(ep -> sb.append("endpoint=").append(ep).append('\n'));
+        persistentKeepalive.ifPresent(pk -> sb.append("persistent_keepalive_interval=").append(pk).append('\n'));
+        preSharedKey.ifPresent(psk -> sb.append("preshared_key=").append(psk.toHex()).append('\n'));
+        return sb.toString();
+    }
+
+    @SuppressWarnings("UnusedReturnValue")
+    public static final class Builder {
+        // See wg(8)
+        private static final int MAX_PERSISTENT_KEEPALIVE = 65535;
+
+        // Defaults to an empty set.
+        private final Set<InetNetwork> allowedIps = new LinkedHashSet<>();
+        // Defaults to not present.
+        private Optional<InetEndpoint> endpoint = Optional.empty();
+        // Defaults to not present.
+        private Optional<Integer> persistentKeepalive = Optional.empty();
+        // Defaults to not present.
+        private Optional<Key> preSharedKey = Optional.empty();
+        // No default; must be provided before building.
+        @Nullable private Key publicKey;
+
+        public Builder addAllowedIp(final InetNetwork allowedIp) {
+            allowedIps.add(allowedIp);
+            return this;
+        }
+
+        public Builder addAllowedIps(final Collection<InetNetwork> allowedIps) {
+            this.allowedIps.addAll(allowedIps);
+            return this;
+        }
+
+        public Peer build() throws BadConfigException {
+            if (publicKey == null)
+                throw new BadConfigException(Section.PEER, Location.PUBLIC_KEY,
+                        Reason.MISSING_ATTRIBUTE, null);
+            return new Peer(this);
+        }
+
+        public Builder parseAllowedIPs(final CharSequence allowedIps) throws BadConfigException {
+            try {
+                for (final String allowedIp : Attribute.split(allowedIps))
+                    addAllowedIp(InetNetwork.parse(allowedIp));
+                return this;
+            } catch (final ParseException e) {
+                throw new BadConfigException(Section.PEER, Location.ALLOWED_IPS, e);
+            }
+        }
+
+        public Builder parseEndpoint(final String endpoint) throws BadConfigException {
+            try {
+                return setEndpoint(InetEndpoint.parse(endpoint));
+            } catch (final ParseException e) {
+                throw new BadConfigException(Section.PEER, Location.ENDPOINT, e);
+            }
+        }
+
+        public Builder parsePersistentKeepalive(final String persistentKeepalive)
+                throws BadConfigException {
+            try {
+                return setPersistentKeepalive(Integer.parseInt(persistentKeepalive));
+            } catch (final NumberFormatException e) {
+                throw new BadConfigException(Section.PEER, Location.PERSISTENT_KEEPALIVE,
+                        persistentKeepalive, e);
+            }
+        }
+
+        public Builder parsePreSharedKey(final String preSharedKey) throws BadConfigException {
+            try {
+                return setPreSharedKey(Key.fromBase64(preSharedKey));
+            } catch (final KeyFormatException e) {
+                throw new BadConfigException(Section.PEER, Location.PRE_SHARED_KEY, e);
+            }
+        }
+
+        public Builder parsePublicKey(final String publicKey) throws BadConfigException {
+            try {
+                return setPublicKey(Key.fromBase64(publicKey));
+            } catch (final KeyFormatException e) {
+                throw new BadConfigException(Section.PEER, Location.PUBLIC_KEY, e);
+            }
+        }
+
+        public Builder setEndpoint(final InetEndpoint endpoint) {
+            this.endpoint = Optional.of(endpoint);
+            return this;
+        }
+
+        public Builder setPersistentKeepalive(final int persistentKeepalive)
+                throws BadConfigException {
+            if (persistentKeepalive < 0 || persistentKeepalive > MAX_PERSISTENT_KEEPALIVE)
+                throw new BadConfigException(Section.PEER, Location.PERSISTENT_KEEPALIVE,
+                        Reason.INVALID_VALUE, String.valueOf(persistentKeepalive));
+            this.persistentKeepalive = persistentKeepalive == 0 ?
+                    Optional.empty() : Optional.of(persistentKeepalive);
+            return this;
+        }
+
+        public Builder setPreSharedKey(final Key preSharedKey) {
+            this.preSharedKey = Optional.of(preSharedKey);
+            return this;
+        }
+
+        public Builder setPublicKey(final Key publicKey) {
+            this.publicKey = publicKey;
+            return this;
+        }
+    }
+}
diff --git a/tunnel/src/main/java/com/wireguard/crypto/Curve25519.java b/tunnel/src/main/java/com/wireguard/crypto/Curve25519.java
new file mode 100644
index 00000000..5622fc5f
--- /dev/null
+++ b/tunnel/src/main/java/com/wireguard/crypto/Curve25519.java
@@ -0,0 +1,497 @@
+/*
+ * Copyright © 2016 Southern Storm Software, Pty Ltd.
+ * Copyright © 2017-2019 WireGuard LLC. All Rights Reserved.
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package com.wireguard.crypto;
+
+import androidx.annotation.Nullable;
+
+import java.util.Arrays;
+
+/**
+ * Implementation of the Curve25519 elliptic curve algorithm.
+ * <p>
+ * This implementation was imported to WireGuard from noise-java:
+ * https://github.com/rweather/noise-java
+ * <p>
+ * This implementation is based on that from arduinolibs:
+ * https://github.com/rweather/arduinolibs
+ * <p>
+ * Differences in this version are due to using 26-bit limbs for the
+ * representation instead of the 8/16/32-bit limbs in the original.
+ * <p>
+ * References: http://cr.yp.to/ecdh.html, RFC 7748
+ */
+@SuppressWarnings({"MagicNumber", "NonConstantFieldWithUpperCaseName", "SuspiciousNameCombination"})
+public final class Curve25519 {
+    // Numbers modulo 2^255 - 19 are broken up into ten 26-bit words.
+    private static final int NUM_LIMBS_255BIT = 10;
+    private static final int NUM_LIMBS_510BIT = 20;
+
+    private final int[] A;
+    private final int[] AA;
+    private final int[] B;
+    private final int[] BB;
+    private final int[] C;
+    private final int[] CB;
+    private final int[] D;
+    private final int[] DA;
+    private final int[] E;
+    private final long[] t1;
+    private final int[] t2;
+    private final int[] x_1;
+    private final int[] x_2;
+    private final int[] x_3;
+    private final int[] z_2;
+    private final int[] z_3;
+
+    /**
+     * Constructs the temporary state holder for Curve25519 evaluation.
+     */
+    private Curve25519() {
+        // Allocate memory for all of the temporary variables we will need.
+        x_1 = new int[NUM_LIMBS_255BIT];
+        x_2 = new int[NUM_LIMBS_255BIT];
+        x_3 = new int[NUM_LIMBS_255BIT];
+        z_2 = new int[NUM_LIMBS_255BIT];
+        z_3 = new int[NUM_LIMBS_255BIT];
+        A = new int[NUM_LIMBS_255BIT];
+        B = new int[NUM_LIMBS_255BIT];
+        C = new int[NUM_LIMBS_255BIT];
+        D = new int[NUM_LIMBS_255BIT];
+        E = new int[NUM_LIMBS_255BIT];
+        AA = new int[NUM_LIMBS_255BIT];
+        BB = new int[NUM_LIMBS_255BIT];
+        DA = new int[NUM_LIMBS_255BIT];
+        CB = new int[NUM_LIMBS_255BIT];
+        t1 = new long[NUM_LIMBS_510BIT];
+        t2 = new int[NUM_LIMBS_510BIT];
+    }
+
+    /**
+     * Conditional swap of two values.
+     *
+     * @param select Set to 1 to swap, 0 to leave as-is.
+     * @param x      The first value.
+     * @param y      The second value.
+     */
+    private static void cswap(int select, final int[] x, final int[] y) {
+        select = -select;
+        for (int index = 0; index < NUM_LIMBS_255BIT; ++index) {
+            final int dummy = select & (x[index] ^ y[index]);
+            x[index] ^= dummy;
+            y[index] ^= dummy;
+        }
+    }
+
+    /**
+     * Evaluates the Curve25519 curve.
+     *
+     * @param result     Buffer to place the result of the evaluation into.
+     * @param offset     Offset into the result buffer.
+     * @param privateKey The private key to use in the evaluation.
+     * @param publicKey  The public key to use in the evaluation, or null
+     *                   if the base point of the curve should be used.
+     */
+    public static void eval(final byte[] result, final int offset,
+                            final byte[] privateKey, @Nullable final byte[] publicKey) {
+        final Curve25519 state = new Curve25519();
+        try {
+            // Unpack the public key value.  If null, use 9 as the base point.
+            Arrays.fill(state.x_1, 0);
+            if (publicKey != null) {
+                // Convert the input value from little-endian into 26-bit limbs.
+                for (int index = 0; index < 32; ++index) {
+                    final int bit = (index * 8) % 26;
+                    final int word = (index * 8) / 26;
+                    final int value = publicKey[index] & 0xFF;
+                    if (bit <= (26 - 8)) {
+                        state.x_1[word] |= value << bit;
+                    } else {
+                        state.x_1[word] |= value << bit;
+                        state.x_1[word] &= 0x03FFFFFF;
+                        state.x_1[word + 1] |= value >> (26 - bit);
+                    }
+                }
+
+                // Just in case, we reduce the number modulo 2^255 - 19 to
+                // make sure that it is in range of the field before we start.
+                // This eliminates values between 2^255 - 19 and 2^256 - 1.
+                state.reduceQuick(state.x_1);
+                state.reduceQuick(state.x_1);
+            } else {
+                state.x_1[0] = 9;
+            }
+
+            // Initialize the other temporary variables.
+            Arrays.fill(state.x_2, 0);            // x_2 = 1
+            state.x_2[0] = 1;
+            Arrays.fill(state.z_2, 0);            // z_2 = 0
+            System.arraycopy(state.x_1, 0, state.x_3, 0, state.x_1.length);  // x_3 = x_1
+            Arrays.fill(state.z_3, 0);            // z_3 = 1
+            state.z_3[0] = 1;
+
+            // Evaluate the curve for every bit of the private key.
+            state.evalCurve(privateKey);
+
+            // Compute x_2 * (z_2 ^ (p - 2)) where p = 2^255 - 19.
+            state.recip(state.z_3, state.z_2);
+            state.mul(state.x_2, state.x_2, state.z_3);
+
+            // Convert x_2 into little-endian in the result buffer.
+            for (int index = 0; index < 32; ++index) {
+                final int bit = (index * 8) % 26;
+                final int word = (index * 8) / 26;
+                if (bit <= (26 - 8))
+                    result[offset + index] = (byte) (state.x_2[word] >> bit);
+                else
+                    result[offset + index] = (byte) ((state.x_2[word] >> bit) | (state.x_2[word + 1] << (26 - bit)));
+            }
+        } finally {
+            // Clean up all temporary state before we exit.
+            state.destroy();
+        }
+    }
+
+    /**
+     * Subtracts two numbers modulo 2^255 - 19.
+     *
+     * @param result The result.
+     * @param x      The first number to subtract.
+     * @param y      The second number to subtract.
+     */
+    private static void sub(final int[] result, final int[] x, final int[] y) {
+        int index;
+        int borrow;
+
+        // Subtract y from x to generate the intermediate result.
+        borrow = 0;
+        for (index = 0; index < NUM_LIMBS_255BIT; ++index) {
+            borrow = x[index] - y[index] - ((borrow >> 26) & 0x01);
+            result[index] = borrow & 0x03FFFFFF;
+        }
+
+        // If we had a borrow, then the result has gone negative and we
+        // have to add 2^255 - 19 to the result to make it positive again.
+        // The top bits of "borrow" will be all 1's if there is a borrow
+        // or it will be all 0's if there was no borrow.  Easiest is to
+        // conditionally subtract 19 and then mask off the high bits.
+        borrow = result[0] - ((-((borrow >> 26) & 0x01)) & 19);
+        result[0] = borrow & 0x03FFFFFF;
+        for (index = 1; index < NUM_LIMBS_255BIT; ++index) {
+            borrow = result[index] - ((borrow >> 26) & 0x01);
+            result[index] = borrow & 0x03FFFFFF;
+        }
+        result[NUM_LIMBS_255BIT - 1] &= 0x001FFFFF;
+    }
+
+    /**
+     * Adds two numbers modulo 2^255 - 19.
+     *
+     * @param result The result.
+     * @param x      The first number to add.
+     * @param y      The second number to add.
+     */
+    private void add(final int[] result, final int[] x, final int[] y) {
+        int carry = x[0] + y[0];
+        result[0] = carry & 0x03FFFFFF;
+        for (int index = 1; index < NUM_LIMBS_255BIT; ++index) {
+            carry = (carry >> 26) + x[index] + y[index];
+            result[index] = carry & 0x03FFFFFF;
+        }
+        reduceQuick(result);
+    }
+
+    /**
+     * Destroy all sensitive data in this object.
+     */
+    private void destroy() {
+        // Destroy all temporary variables.
+        Arrays.fill(x_1, 0);
+        Arrays.fill(x_2, 0);
+        Arrays.fill(x_3, 0);
+        Arrays.fill(z_2, 0);
+        Arrays.fill(z_3, 0);
+        Arrays.fill(A, 0);
+        Arrays.fill(B, 0);
+        Arrays.fill(C, 0);
+        Arrays.fill(D, 0);
+        Arrays.fill(E, 0);
+        Arrays.fill(AA, 0);
+        Arrays.fill(BB, 0);
+        Arrays.fill(DA, 0);
+        Arrays.fill(CB, 0);
+        Arrays.fill(t1, 0L);
+        Arrays.fill(t2, 0);
+    }
+
+    /**
+     * Evaluates the curve for every bit in a secret key.
+     *
+     * @param s The 32-byte secret key.
+     */
+    private void evalCurve(final byte[] s) {
+        int sposn = 31;
+        int sbit = 6;
+        int svalue = s[sposn] | 0x40;
+        int swap = 0;
+
+        // Iterate over all 255 bits of "s" from the highest to the lowest.
+        // We ignore the high bit of the 256-bit representation of "s".
+        while (true) {
+            // Conditional swaps on entry to this bit but only if we
+            // didn't swap on the previous bit.
+            final int select = (svalue >> sbit) & 0x01;
+            swap ^= select;
+            cswap(swap, x_2, x_3);
+            cswap(swap, z_2, z_3);
+            swap = select;
+
+            // Evaluate the curve.
+            add(A, x_2, z_2);               // A = x_2 + z_2
+            square(AA, A);                  // AA = A^2
+            sub(B, x_2, z_2);               // B = x_2 - z_2
+            square(BB, B);                  // BB = B^2
+            sub(E, AA, BB);                 // E = AA - BB
+            add(C, x_3, z_3);               // C = x_3 + z_3
+            sub(D, x_3, z_3);               // D = x_3 - z_3
+            mul(DA, D, A);                  // DA = D * A
+            mul(CB, C, B);                  // CB = C * B
+            add(x_3, DA, CB);               // x_3 = (DA + CB)^2
+            square(x_3, x_3);
+            sub(z_3, DA, CB);               // z_3 = x_1 * (DA - CB)^2
+            square(z_3, z_3);
+            mul(z_3, z_3, x_1);
+            mul(x_2, AA, BB);               // x_2 = AA * BB
+            mulA24(z_2, E);                 // z_2 = E * (AA + a24 * E)
+            add(z_2, z_2, AA);
+            mul(z_2, z_2, E);
+
+            // Move onto the next lower bit of "s".
+            if (sbit > 0) {
+                --sbit;
+            } else if (sposn == 0) {
+                break;
+            } else if (sposn == 1) {
+                --sposn;
+                svalue = s[sposn] & 0xF8;
+                sbit = 7;
+            } else {
+                --sposn;
+                svalue = s[sposn];
+                sbit = 7;
+            }
+        }
+
+        // Final conditional swaps.
+        cswap(swap, x_2, x_3);
+        cswap(swap, z_2, z_3);
+    }
+
+    /**
+     * Multiplies two numbers modulo 2^255 - 19.
+     *
+     * @param result The result.
+     * @param x      The first number to multiply.
+     * @param y      The second number to multiply.
+     */
+    private void mul(final int[] result, final int[] x, final int[] y) {
+        // Multiply the two numbers to create the intermediate result.
+        long v = x[0];
+        for (int i = 0; i < NUM_LIMBS_255BIT; ++i) {
+            t1[i] = v * y[i];
+        }
+        for (int i = 1; i < NUM_LIMBS_255BIT; ++i) {
+            v = x[i];
+            for (int j = 0; j < (NUM_LIMBS_255BIT - 1); ++j) {
+                t1[i + j] += v * y[j];
+            }
+            t1[i + NUM_LIMBS_255BIT - 1] = v * y[NUM_LIMBS_255BIT - 1];
+        }
+
+        // Propagate carries and convert back into 26-bit words.
+        v = t1[0];
+        t2[0] = ((int) v) & 0x03FFFFFF;
+        for (int i = 1; i < NUM_LIMBS_510BIT; ++i) {
+            v = (v >> 26) + t1[i];
+            t2[i] = ((int) v) & 0x03FFFFFF;
+        }
+
+        // Reduce the result modulo 2^255 - 19.
+        reduce(result, t2, NUM_LIMBS_255BIT);
+    }
+
+    /**
+     * Multiplies a number by the a24 constant, modulo 2^255 - 19.
+     *
+     * @param result The result.
+     * @param x      The number to multiply by a24.
+     */
+    private void mulA24(final int[] result, final int[] x) {
+        final long a24 = 121665;
+        long carry = 0;
+        for (int index = 0; index < NUM_LIMBS_255BIT; ++index) {
+            carry += a24 * x[index];
+            t2[index] = ((int) carry) & 0x03FFFFFF;
+            carry >>= 26;
+        }
+        t2[NUM_LIMBS_255BIT] = ((int) carry) & 0x03FFFFFF;
+        reduce(result, t2, 1);
+    }
+
+    /**
+     * Raise x to the power of (2^250 - 1).
+     *
+     * @param result The result.  Must not overlap with x.
+     * @param x      The argument.
+     */
+    private void pow250(final int[] result, final int[] x) {
+        // The big-endian hexadecimal expansion of (2^250 - 1) is:
+        // 03FFFFFF FFFFFFFF FFFFFFFF FFFFFFFF FFFFFFFF FFFFFFFF FFFFFFFF FFFFFFFF
+        //
+        // The naive implementation needs to do 2 multiplications per 1 bit and
+        // 1 multiplication per 0 bit.  We can improve upon this by creating a
+        // pattern 0000000001 ... 0000000001.  If we square and multiply the
+        // pattern by itself we can turn the pattern into the partial results
+        // 0000000011 ... 0000000011, 0000000111 ... 0000000111, etc.
+        // This averages out to about 1.1 multiplications per 1 bit instead of 2.
+
+        // Build a pattern of 250 bits in length of repeated copies of 0000000001.
+        square(A, x);
+        for (int j = 0; j < 9; ++j)
+            square(A, A);
+        mul(result, A, x);
+        for (int i = 0; i < 23; ++i) {
+            for (int j = 0; j < 10; ++j)
+                square(A, A);
+            mul(result, result, A);
+        }
+
+        // Multiply bit-shifted versions of the 0000000001 pattern into
+        // the result to "fill in" the gaps in the pattern.
+        square(A, result);
+        mul(result, result, A);
+        for (int j = 0; j < 8; ++j) {
+            square(A, A);
+            mul(result, result, A);
+        }
+    }
+
+    /**
+     * Computes the reciprocal of a number modulo 2^255 - 19.
+     *
+     * @param result The result.  Must not overlap with x.
+     * @param x      The argument.
+     */
+    private void recip(final int[] result, final int[] x) {
+        // The reciprocal is the same as x ^ (p - 2) where p = 2^255 - 19.
+        // The big-endian hexadecimal expansion of (p - 2) is:
+        // 7FFFFFFF FFFFFFFF FFFFFFFF FFFFFFFF FFFFFFFF FFFFFFFF FFFFFFFF FFFFFFEB
+        // Start with the 250 upper bits of the expansion of (p - 2).
+        pow250(result, x);
+
+        // Deal with the 5 lowest bits of (p - 2), 01011, from highest to lowest.
+        square(result, result);
+        square(result, result);
+        mul(result, result, x);
+        square(result, result);
+        square(result, result);
+        mul(result, result, x);
+        square(result, result);
+        mul(result, result, x);
+    }
+
+    /**
+     * Reduce a number modulo 2^255 - 19.
+     *
+     * @param result The result.
+     * @param x      The value to be reduced.  This array will be
+     *               modified during the reduction.
+     * @param size   The number of limbs in the high order half of x.
+     */
+    private void reduce(final int[] result, final int[] x, final int size) {
+        // Calculate (x mod 2^255) + ((x / 2^255) * 19) which will
+        // either produce the answer we want or it will produce a
+        // value of the form "answer + j * (2^255 - 19)".  There are
+        // 5 left-over bits in the top-most limb of the bottom half.
+        int carry = 0;
+        int limb = x[NUM_LIMBS_255BIT - 1] >> 21;
+        x[NUM_LIMBS_255BIT - 1] &= 0x001FFFFF;
+        for (int index = 0; index < size; ++index) {
+            limb += x[NUM_LIMBS_255BIT + index] << 5;
+            carry += (limb & 0x03FFFFFF) * 19 + x[index];
+            x[index] = carry & 0x03FFFFFF;
+            limb >>= 26;
+            carry >>= 26;
+        }
+        if (size < NUM_LIMBS_255BIT) {
+            // The high order half of the number is short; e.g. for mulA24().
+            // Propagate the carry through the rest of the low order part.
+            for (int index = size; index < NUM_LIMBS_255BIT; ++index) {
+                carry += x[index];
+                x[index] = carry & 0x03FFFFFF;
+                carry >>= 26;
+            }
+        }
+
+        // The "j" value may still be too large due to the final carry-out.
+        // We must repeat the reduction.  If we already have the answer,
+        // then this won't do any harm but we must still do the calculation
+        // to preserve the overall timing.  The "j" value will be between
+        // 0 and 19, which means that the carry we care about is in the
+        // top 5 bits of the highest limb of the bottom half.
+        carry = (x[NUM_LIMBS_255BIT - 1] >> 21) * 19;
+        x[NUM_LIMBS_255BIT - 1] &= 0x001FFFFF;
+        for (int index = 0; index < NUM_LIMBS_255BIT; ++index) {
+            carry += x[index];
+            result[index] = carry & 0x03FFFFFF;
+            carry >>= 26;
+        }
+
+        // At this point "x" will either be the answer or it will be the
+        // answer plus (2^255 - 19).  Perform a trial subtraction to
+        // complete the reduction process.
+        reduceQuick(result);
+    }
+
+    /**
+     * Reduces a number modulo 2^255 - 19 where it is known that the
+     * number can be reduced with only 1 trial subtraction.
+     *
+     * @param x The number to reduce, and the result.
+     */
+    private void reduceQuick(final int[] x) {
+        // Perform a trial subtraction of (2^255 - 19) from "x" which is
+        // equivalent to adding 19 and subtracting 2^255.  We add 19 here;
+        // the subtraction of 2^255 occurs in the next step.
+        int carry = 19;
+        for (int index = 0; index < NUM_LIMBS_255BIT; ++index) {
+            carry += x[index];
+            t2[index] = carry & 0x03FFFFFF;
+            carry >>= 26;
+        }
+
+        // If there was a borrow, then the original "x" is the correct answer.
+        // If there was no borrow, then "t2" is the correct answer.  Select the
+        // correct answer but do it in a way that instruction timing will not
+        // reveal which value was selected.  Borrow will occur if bit 21 of
+        // "t2" is zero.  Turn the bit into a selection mask.
+        final int mask = -((t2[NUM_LIMBS_255BIT - 1] >> 21) & 0x01);
+        final int nmask = ~mask;
+        t2[NUM_LIMBS_255BIT - 1] &= 0x001FFFFF;
+        for (int index = 0; index < NUM_LIMBS_255BIT; ++index)
+            x[index] = (x[index] & nmask) | (t2[index] & mask);
+    }
+
+    /**
+     * Squares a number modulo 2^255 - 19.
+     *
+     * @param result The result.
+     * @param x      The number to square.
+     */
+    private void square(final int[] result, final int[] x) {
+        mul(result, x, x);
+    }
+}
diff --git a/tunnel/src/main/java/com/wireguard/crypto/Key.java b/tunnel/src/main/java/com/wireguard/crypto/Key.java
new file mode 100644
index 00000000..6648a5f3
--- /dev/null
+++ b/tunnel/src/main/java/com/wireguard/crypto/Key.java
@@ -0,0 +1,288 @@
+/*
+ * Copyright © 2017-2019 WireGuard LLC. All Rights Reserved.
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package com.wireguard.crypto;
+
+import com.wireguard.crypto.KeyFormatException.Type;
+
+import java.security.MessageDigest;
+import java.security.SecureRandom;
+import java.util.Arrays;
+
+/**
+ * Represents a WireGuard public or private key. This class uses specialized constant-time base64
+ * and hexadecimal codec implementations that resist side-channel attacks.
+ * <p>
+ * Instances of this class are immutable.
+ */
+@SuppressWarnings("MagicNumber")
+public final class Key {
+    private final byte[] key;
+
+    /**
+     * Constructs an object encapsulating the supplied key.
+     *
+     * @param key an array of bytes containing a binary key. Callers of this constructor are
+     *            responsible for ensuring that the array is of the correct length.
+     */
+    private Key(final byte[] key) {
+        // Defensively copy to ensure immutability.
+        this.key = Arrays.copyOf(key, key.length);
+    }
+
+    /**
+     * Decodes a single 4-character base64 chunk to an integer in constant time.
+     *
+     * @param src       an array of at least 4 characters in base64 format
+     * @param srcOffset the offset of the beginning of the chunk in {@code src}
+     * @return the decoded 3-byte integer, or some arbitrary integer value if the input was not
+     * valid base64
+     */
+    private static int decodeBase64(final char[] src, final int srcOffset) {
+        int val = 0;
+        for (int i = 0; i < 4; ++i) {
+            final char c = src[i + srcOffset];
+            val |= (-1
+                    + ((((('A' - 1) - c) & (c - ('Z' + 1))) >>> 8) & (c - 64))
+                    + ((((('a' - 1) - c) & (c - ('z' + 1))) >>> 8) & (c - 70))
+                    + ((((('0' - 1) - c) & (c - ('9' + 1))) >>> 8) & (c + 5))
+                    + ((((('+' - 1) - c) & (c - ('+' + 1))) >>> 8) & 63)
+                    + ((((('/' - 1) - c) & (c - ('/' + 1))) >>> 8) & 64)
+            ) << (18 - 6 * i);
+        }
+        return val;
+    }
+
+    /**
+     * Encodes a single 4-character base64 chunk from 3 consecutive bytes in constant time.
+     *
+     * @param src        an array of at least 3 bytes
+     * @param srcOffset  the offset of the beginning of the chunk in {@code src}
+     * @param dest       an array of at least 4 characters
+     * @param destOffset the offset of the beginning of the chunk in {@code dest}
+     */
+    private static void encodeBase64(final byte[] src, final int srcOffset,
+                                     final char[] dest, final int destOffset) {
+        final byte[] input = {
+                (byte) ((src[srcOffset] >>> 2) & 63),
+                (byte) ((src[srcOffset] << 4 | ((src[1 + srcOffset] & 0xff) >>> 4)) & 63),
+                (byte) ((src[1 + srcOffset] << 2 | ((src[2 + srcOffset] & 0xff) >>> 6)) & 63),
+                (byte) ((src[2 + srcOffset]) & 63),
+        };
+        for (int i = 0; i < 4; ++i) {
+            dest[i + destOffset] = (char) (input[i] + 'A'
+                    + (((25 - input[i]) >>> 8) & 6)
+                    - (((51 - input[i]) >>> 8) & 75)
+                    - (((61 - input[i]) >>> 8) & 15)
+                    + (((62 - input[i]) >>> 8) & 3));
+        }
+    }
+
+    /**
+     * Decodes a WireGuard public or private key from its base64 string representation. This
+     * function throws a {@link KeyFormatException} if the source string is not well-formed.
+     *
+     * @param str the base64 string representation of a WireGuard key
+     * @return the decoded key encapsulated in an immutable container
+     */
+    public static Key fromBase64(final String str) throws KeyFormatException {
+        final char[] input = str.toCharArray();
+        if (input.length != Format.BASE64.length || input[Format.BASE64.length - 1] != '=')
+            throw new KeyFormatException(Format.BASE64, Type.LENGTH);
+        final byte[] key = new byte[Format.BINARY.length];
+        int i;
+        int ret = 0;
+        for (i = 0; i < key.length / 3; ++i) {
+            final int val = decodeBase64(input, i * 4);
+            ret |= val >>> 31;
+            key[i * 3] = (byte) ((val >>> 16) & 0xff);
+            key[i * 3 + 1] = (byte) ((val >>> 8) & 0xff);
+            key[i * 3 + 2] = (byte) (val & 0xff);
+        }
+        final char[] endSegment = {
+                input[i * 4],
+                input[i * 4 + 1],
+                input[i * 4 + 2],
+                'A',
+        };
+        final int val = decodeBase64(endSegment, 0);
+        ret |= (val >>> 31) | (val & 0xff);
+        key[i * 3] = (byte) ((val >>> 16) & 0xff);
+        key[i * 3 + 1] = (byte) ((val >>> 8) & 0xff);
+
+        if (ret != 0)
+            throw new KeyFormatException(Format.BASE64, Type.CONTENTS);
+        return new Key(key);
+    }
+
+    /**
+     * Wraps a WireGuard public or private key in an immutable container. This function throws a
+     * {@link KeyFormatException} if the source data is not the correct length.
+     *
+     * @param bytes an array of bytes containing a WireGuard key in binary format
+     * @return the key encapsulated in an immutable container
+     */
+    public static Key fromBytes(final byte[] bytes) throws KeyFormatException {
+        if (bytes.length != Format.BINARY.length)
+            throw new KeyFormatException(Format.BINARY, Type.LENGTH);
+        return new Key(bytes);
+    }
+
+    /**
+     * Decodes a WireGuard public or private key from its hexadecimal string representation. This
+     * function throws a {@link KeyFormatException} if the source string is not well-formed.
+     *
+     * @param str the hexadecimal string representation of a WireGuard key
+     * @return the decoded key encapsulated in an immutable container
+     */
+    public static Key fromHex(final String str) throws KeyFormatException {
+        final char[] input = str.toCharArray();
+        if (input.length != Format.HEX.length)
+            throw new KeyFormatException(Format.HEX, Type.LENGTH);
+        final byte[] key = new byte[Format.BINARY.length];
+        int ret = 0;
+        for (int i = 0; i < key.length; ++i) {
+            int c;
+            int cNum;
+            int cNum0;
+            int cAlpha;
+            int cAlpha0;
+            int cVal;
+            final int cAcc;
+
+            c = input[i * 2];
+            cNum = c ^ 48;
+            cNum0 = ((cNum - 10) >>> 8) & 0xff;
+            cAlpha = (c & ~32) - 55;
+            cAlpha0 = (((cAlpha - 10) ^ (cAlpha - 16)) >>> 8) & 0xff;
+            ret |= ((cNum0 | cAlpha0) - 1) >>> 8;
+            cVal = (cNum0 & cNum) | (cAlpha0 & cAlpha);
+            cAcc = cVal * 16;
+
+            c = input[i * 2 + 1];
+            cNum = c ^ 48;
+            cNum0 = ((cNum - 10) >>> 8) & 0xff;
+            cAlpha = (c & ~32) - 55;
+            cAlpha0 = (((cAlpha - 10) ^ (cAlpha - 16)) >>> 8) & 0xff;
+            ret |= ((cNum0 | cAlpha0) - 1) >>> 8;
+            cVal = (cNum0 & cNum) | (cAlpha0 & cAlpha);
+            key[i] = (byte) (cAcc | cVal);
+        }
+        if (ret != 0)
+            throw new KeyFormatException(Format.HEX, Type.CONTENTS);
+        return new Key(key);
+    }
+
+    /**
+     * Generates a private key using the system's {@link SecureRandom} number generator.
+     *
+     * @return a well-formed random private key
+     */
+    static Key generatePrivateKey() {
+        final SecureRandom secureRandom = new SecureRandom();
+        final byte[] privateKey = new byte[Format.BINARY.getLength()];
+        secureRandom.nextBytes(privateKey);
+        privateKey[0] &= 248;
+        privateKey[31] &= 127;
+        privateKey[31] |= 64;
+        return new Key(privateKey);
+    }
+
+    /**
+     * Generates a public key from an existing private key.
+     *
+     * @param privateKey a private key
+     * @return a well-formed public key that corresponds to the supplied private key
+     */
+    static Key generatePublicKey(final Key privateKey) {
+        final byte[] publicKey = new byte[Format.BINARY.getLength()];
+        Curve25519.eval(publicKey, 0, privateKey.getBytes(), null);
+        return new Key(publicKey);
+    }
+
+    /**
+     * Returns the key as an array of bytes.
+     *
+     * @return an array of bytes containing the raw binary key
+     */
+    public byte[] getBytes() {
+        // Defensively copy to ensure immutability.
+        return Arrays.copyOf(key, key.length);
+    }
+
+    /**
+     * Encodes the key to base64.
+     *
+     * @return a string containing the encoded key
+     */
+    public String toBase64() {
+        final char[] output = new char[Format.BASE64.length];
+        int i;
+        for (i = 0; i < key.length / 3; ++i)
+            encodeBase64(key, i * 3, output, i * 4);
+        final byte[] endSegment = {
+                key[i * 3],
+                key[i * 3 + 1],
+                0,
+        };
+        encodeBase64(endSegment, 0, output, i * 4);
+        output[Format.BASE64.length - 1] = '=';
+        return new String(output);
+    }
+
+    /**
+     * Encodes the key to hexadecimal ASCII characters.
+     *
+     * @return a string containing the encoded key
+     */
+    public String toHex() {
+        final char[] output = new char[Format.HEX.length];
+        for (int i = 0; i < key.length; ++i) {
+            output[i * 2] = (char) (87 + (key[i] >> 4 & 0xf)
+                    + ((((key[i] >> 4 & 0xf) - 10) >> 8) & ~38));
+            output[i * 2 + 1] = (char) (87 + (key[i] & 0xf)
+                    + ((((key[i] & 0xf) - 10) >> 8) & ~38));
+        }
+        return new String(output);
+    }
+
+    @Override
+    public int hashCode() {
+        int ret = 0;
+        for (int i = 0; i < key.length / 4; ++i)
+            ret ^= (key[i * 4 + 0] >> 0) + (key[i * 4 + 1] >> 8) + (key[i * 4 + 2] >> 16) + (key[i * 4 + 3] >> 24);
+        return ret;
+    }
+
+    @Override
+    public boolean equals(final Object obj) {
+        if (obj == this)
+            return true;
+        if (obj == null || obj.getClass() != getClass())
+            return false;
+        final Key other = (Key) obj;
+        return MessageDigest.isEqual(key, other.key);
+    }
+
+    /**
+     * The supported formats for encoding a WireGuard key.
+     */
+    public enum Format {
+        BASE64(44),
+        BINARY(32),
+        HEX(64);
+
+        private final int length;
+
+        Format(final int length) {
+            this.length = length;
+        }
+
+        public int getLength() {
+            return length;
+        }
+    }
+
+}
diff --git a/tunnel/src/main/java/com/wireguard/crypto/KeyFormatException.java b/tunnel/src/main/java/com/wireguard/crypto/KeyFormatException.java
new file mode 100644
index 00000000..5818b4d4
--- /dev/null
+++ b/tunnel/src/main/java/com/wireguard/crypto/KeyFormatException.java
@@ -0,0 +1,34 @@
+/*
+ * Copyright © 2018-2019 WireGuard LLC. All Rights Reserved.
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package com.wireguard.crypto;
+
+/**
+ * An exception thrown when attempting to parse an invalid key (too short, too long, or byte
+ * data inappropriate for the format). The format being parsed can be accessed with the
+ * {@link #getFormat} method.
+ */
+public final class KeyFormatException extends Exception {
+    private final Key.Format format;
+    private final Type type;
+
+    KeyFormatException(final Key.Format format, final Type type) {
+        this.format = format;
+        this.type = type;
+    }
+
+    public Key.Format getFormat() {
+        return format;
+    }
+
+    public Type getType() {
+        return type;
+    }
+
+    public enum Type {
+        CONTENTS,
+        LENGTH
+    }
+}
diff --git a/tunnel/src/main/java/com/wireguard/crypto/KeyPair.java b/tunnel/src/main/java/com/wireguard/crypto/KeyPair.java
new file mode 100644
index 00000000..f8238e91
--- /dev/null
+++ b/tunnel/src/main/java/com/wireguard/crypto/KeyPair.java
@@ -0,0 +1,51 @@
+/*
+ * Copyright © 2017-2019 WireGuard LLC. All Rights Reserved.
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package com.wireguard.crypto;
+
+/**
+ * Represents a Curve25519 key pair as used by WireGuard.
+ * <p>
+ * Instances of this class are immutable.
+ */
+public class KeyPair {
+    private final Key privateKey;
+    private final Key publicKey;
+
+    /**
+     * Creates a key pair using a newly-generated private key.
+     */
+    public KeyPair() {
+        this(Key.generatePrivateKey());
+    }
+
+    /**
+     * Creates a key pair using an existing private key.
+     *
+     * @param privateKey a private key, used to derive the public key
+     */
+    public KeyPair(final Key privateKey) {
+        this.privateKey = privateKey;
+        publicKey = Key.generatePublicKey(privateKey);
+    }
+
+    /**
+     * Returns the private key from the key pair.
+     *
+     * @return the private key
+     */
+    public Key getPrivateKey() {
+        return privateKey;
+    }
+
+    /**
+     * Returns the public key from the key pair.
+     *
+     * @return the public key
+     */
+    public Key getPublicKey() {
+        return publicKey;
+    }
+}
diff --git a/tunnel/src/main/java/com/wireguard/util/NonNullForAll.java b/tunnel/src/main/java/com/wireguard/util/NonNullForAll.java
new file mode 100644
index 00000000..f179fa49
--- /dev/null
+++ b/tunnel/src/main/java/com/wireguard/util/NonNullForAll.java
@@ -0,0 +1,26 @@
+/*
+ * Copyright © 2017-2019 WireGuard LLC. All Rights Reserved.
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package com.wireguard.util;
+
+import java.lang.annotation.Documented;
+import java.lang.annotation.ElementType;
+import java.lang.annotation.Retention;
+import java.lang.annotation.RetentionPolicy;
+
+import javax.annotation.Nonnull;
+import javax.annotation.meta.TypeQualifierDefault;
+
+/**
+ * This annotation can be applied to a package, class or method to indicate that all
+ * class fields and method parameters and return values in that element are nonnull
+ * by default unless overridden.
+ */
+@Documented
+@Nonnull
+@TypeQualifierDefault({ElementType.FIELD, ElementType.METHOD, ElementType.PARAMETER})
+@Retention(RetentionPolicy.RUNTIME)
+public @interface NonNullForAll {
+}