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KeyEncoding: add constant time hex implementation

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Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
This commit is contained in:
Jason A. Donenfeld 2018-02-12 20:44:36 +01:00
parent b22e2b259b
commit d1c863b16e
1 changed files with 44 additions and 2 deletions
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46
app/src/main/java/com/wireguard/crypto/KeyEncoding.java
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@ -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);
}
}