Remodel the Model

- The configuration and crypto model is now entirely independent
of Android classes other than Nullable and TextUtils.
- Model classes are immutable and use builders that enforce the
appropriate optional/required attributes.
- The Android config proxies (for Parcelable and databinding) are
moved to the Android side of the codebase, and are designed to be
safe for two-way databinding. This allows proper observability in
TunnelDetailFragment.
- Various robustness fixes and documentation updates to helper classes.

Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>

1 files changed, 81 insertions, 0 deletions

diff --git a/app/src/main/java/com/wireguard/crypto/KeyPair.java b/app/src/main/java/com/wireguard/crypto/KeyPair.java
new file mode 100644
index 00000000..2b2bf564
--- /dev/null
+++ b/app/src/main/java/com/wireguard/crypto/KeyPair.java
@@ -0,0 +1,81 @@
+/*
+ * Copyright © 2017-2018 WireGuard LLC. All Rights Reserved.
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package com.wireguard.crypto;
+
+import java.security.SecureRandom;
+
+/**
+ * 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(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 = generatePublicKey(privateKey);
+    }
+
+    /**
+     * Generates a private key using the system's {@link SecureRandom} number generator.
+     *
+     * @return a well-formed random private key
+     */
+    @SuppressWarnings("MagicNumber")
+    private static Key generatePrivateKey() {
+        final SecureRandom secureRandom = new SecureRandom();
+        final byte[] privateKey = new byte[Key.Format.BINARY.getLength()];
+        secureRandom.nextBytes(privateKey);
+        privateKey[0] &= 248;
+        privateKey[31] &= 127;
+        privateKey[31] |= 64;
+        return Key.fromBytes(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
+     */
+    private static Key generatePublicKey(final Key privateKey) {
+        final byte[] publicKey = new byte[Key.Format.BINARY.getLength()];
+        Curve25519.eval(publicKey, 0, privateKey.getBytes(), null);
+        return Key.fromBytes(publicKey);
+    }
+
+    /**
+     * 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;
+    }
+}