public static bool ConfirmEcbMode(int blockSize)
{
var b = SecureRng.GenerateRandomBytes(blockSize);
var duplicateBlocks = new List <byte>();
duplicateBlocks.AddRange(b);
duplicateBlocks.AddRange(b);
var encrypted = EncryptionOracle(duplicateBlocks.ToArray());
return(AesEcb.IsEcbEncrypted(encrypted, blockSize));
}
private static byte[] TransformData(byte[] data)
{
var prefixLength = Rand.Next(MinRandBytesCount, MaxRandBytesCount + 1);
var suffixLength = Rand.Next(MinRandBytesCount, MaxRandBytesCount + 1);
var prefix = SecureRng.GenerateRandomBytes(prefixLength);
var suffix = SecureRng.GenerateRandomBytes(suffixLength);
var input = new List <byte>();
input.AddRange(prefix);
input.AddRange(data);
input.AddRange(suffix);
return(input.ToArray());
}
public void TestChallenge11()
{
var key = SecureRng.GenerateRandomBytes(16);
var data = new List <byte>();
for (int i = 0; i < EcbCbcEncryptionOracleInputLengthBytes; i++)
{
data.Add(0x00);
}
for (int i = 0; i < Challenge11TestCount; i++)
{
var guessedMode =
AesEcbCbcDetectionOracle.EncryptEcbOrCbc(data.ToArray(), out var actualMode);
Assert.AreEqual(actualMode, guessedMode);
}
}
private static byte[] EncryptionOracle(byte[] data)
{
if (_randomPrefix == null || _randomPrefix.Length == 0)
{
var r = new Random();
var prefixLength = r.Next(1, MaxPrefixLength + 1);
_randomPrefix = SecureRng.GenerateRandomBytes(prefixLength);
}
var combined = new List <byte>();
combined.AddRange(_randomPrefix);
combined.AddRange(data);
combined.AddRange(Convert.FromBase64String(EncodedSuffix));
var padded = PaddingUtil.Pad(combined.ToArray(), BlockSizeBytes);
return(AesEcb.Encrypt(Key, padded));
}
public static CipherMode EncryptEcbOrCbc(byte[] data, out CipherMode actualMode)
{
actualMode = Rand.Next(0, 2) == 0 ? CipherMode.ECB : CipherMode.CBC;
var key = SecureRng.GenerateRandomBytes(KeySizeBytes);
// Add prefix and suffix to data
data = TransformData(data);
byte[] encrypted;
if (actualMode == CipherMode.ECB)
{
var padded = PaddingUtil.Pad(data, BlockSizeBytes);
encrypted = AesEcb.Encrypt(key, padded);
}
else
{
var iv = SecureRng.GenerateRandomBytes(BlockSizeBytes);
encrypted = AesCbc.Encrypt(key, iv, data);
}
var guessedMode = AesEcb.IsEcbEncrypted(encrypted, BlockSizeBytes)
? CipherMode.ECB
: CipherMode.CBC;
return(guessedMode);
}