KeyEncoding: add constant time hex implementation

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

1 files changed, 44 insertions, 2 deletions

diff --git a/app/src/main/java/com/wireguard/crypto/KeyEncoding.java b/app/src/main/java/com/wireguard/crypto/KeyEncoding.java
index 99ff0ee9..92e03230 100644
--- a/app/src/main/java/com/wireguard/crypto/KeyEncoding.java
+++ b/app/src/main/java/com/wireguard/crypto/KeyEncoding.java
@@ -3,15 +3,20 @@
 package com.wireguard.crypto;
 
 /**
- * This is a specialized constant-time base64 implementation that resists side-channel attacks.
+ * This is a specialized constant-time base64 and hex implementation that resists side-channel attacks.
  */
 
 @SuppressWarnings("MagicNumber")
 public final class KeyEncoding {
     public static final int KEY_LENGTH = 32;
     public static final int KEY_LENGTH_BASE64 = 44;
+    public static final int KEY_LENGTH_HEX = 64;
     private static final String KEY_LENGTH_BASE64_EXCEPTION_MESSAGE =
             "WireGuard base64 keys must be 44 characters encoding 32 bytes";
+    private static final String KEY_LENGTH_HEX_EXCEPTION_MESSAGE =
+            "WireGuard hex keys must be 64 characters encoding 32 bytes";
+    private static final String KEY_LENGTH_EXCEPTION_MESSAGE =
+            "WireGuard keys must be 32 bytes";
 
     private KeyEncoding() {
         // Prevent instantiation.
@@ -80,7 +85,7 @@ public final class KeyEncoding {
     public static String keyToBase64(final byte[] key) {
         final char[] output = new char[KEY_LENGTH_BASE64];
         if (key.length != KEY_LENGTH)
-            throw new IllegalArgumentException("WireGuard keys must be 32 bytes");
+            throw new IllegalArgumentException(KEY_LENGTH_EXCEPTION_MESSAGE);
         int i;
         for (i = 0; i < KEY_LENGTH / 3; ++i)
             encodeBase64(key, i * 3, output, i * 4);
@@ -93,4 +98,41 @@ public final class KeyEncoding {
         output[KEY_LENGTH_BASE64 - 1] = '=';
         return new String(output);
     }
+
+    public static byte[] keyFromHex(final String str) {
+        final char[] input = str.toCharArray();
+        final byte[] key = new byte[KEY_LENGTH];
+        if (input.length != KEY_LENGTH_HEX)
+            throw new IllegalArgumentException(KEY_LENGTH_HEX_EXCEPTION_MESSAGE);
+
+        int c, c_acc = 0, c_alpha0, c_alpha, c_num0, c_num, c_val, state = 0;
+
+        for (int i = 0; i < KEY_LENGTH_HEX; ++i) {
+            c = input[i];
+            c_num = c ^ 48;
+            c_num0 = (c_num - 10) >>8;
+            c_alpha = (c & ~32) - 55;
+            c_alpha0 = ((c_alpha - 10) ^ (c_alpha - 16)) >> 8;
+            if ((c_num0 | c_alpha0) == 0)
+                throw new IllegalArgumentException(KEY_LENGTH_HEX_EXCEPTION_MESSAGE);
+            c_val = (c_num0 & c_num) | (c_alpha0 & c_alpha);
+            if (state == 0)
+                c_acc = c_val * 16;
+            else
+                key[i / 2] = (byte)(c_acc | c_val);
+            state = ~state;
+        }
+        return key;
+    }
+
+    public static String keyToHex(final byte[] key) {
+        final char[] output = new char[KEY_LENGTH_HEX];
+        if (key.length != KEY_LENGTH)
+            throw new IllegalArgumentException(KEY_LENGTH_EXCEPTION_MESSAGE);
+        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);
+    }
 }