diff options
| -rw-r--r-- | crypto/src/crypto/macs/CMac.cs | 36 |
1 files changed, 23 insertions, 13 deletions
diff --git a/crypto/src/crypto/macs/CMac.cs b/crypto/src/crypto/macs/CMac.cs index 997145a4d..b55a05605 100644 --- a/crypto/src/crypto/macs/CMac.cs +++ b/crypto/src/crypto/macs/CMac.cs @@ -105,20 +105,30 @@ namespace Org.BouncyCastle.Crypto.Macs get { return cipher.AlgorithmName; } } - private static byte[] doubleLu( - byte[] inBytes) + private static int ShiftLeft(byte[] block, byte[] output) { - int FirstBit = (inBytes[0] & 0xFF) >> 7; - byte[] ret = new byte[inBytes.Length]; - for (int i = 0; i < inBytes.Length - 1; i++) + int i = 16; + uint bit = 0; + while (--i >= 0) { - ret[i] = (byte)((inBytes[i] << 1) + ((inBytes[i + 1] & 0xFF) >> 7)); - } - ret[inBytes.Length - 1] = (byte)(inBytes[inBytes.Length - 1] << 1); - if (FirstBit == 1) - { - ret[inBytes.Length - 1] ^= inBytes.Length == 16 ? CONSTANT_128 : CONSTANT_64; + uint b = block[i]; + output[i] = (byte)((b << 1) | bit); + bit = (b >> 7) & 1; } + return (int)bit; + } + + private static byte[] DoubleLu(byte[] input) + { + byte[] ret = new byte[input.Length]; + int carry = ShiftLeft(input, ret); + int xor = input.Length == 16 ? CONSTANT_128 : CONSTANT_64; + + /* + * NOTE: This construction is an attempt at a constant-time implementation. + */ + ret[input.Length - 1] ^= (byte)(xor >> ((1 - carry) << 3)); + return ret; } @@ -132,8 +142,8 @@ namespace Org.BouncyCastle.Crypto.Macs //initializes the L, Lu, Lu2 numbers L = new byte[ZEROES.Length]; cipher.ProcessBlock(ZEROES, 0, L, 0); - Lu = doubleLu(L); - Lu2 = doubleLu(Lu); + Lu = DoubleLu(L); + Lu2 = DoubleLu(Lu); } else if (parameters != null) { |