protected virtual byte[] DecryptWith(byte[] workBuffer, int[] workLens, byte[] key, byte[] iv, KeyUsage usage)
{
var confounderLen = workLens[0];
var checksumLen = workLens[1];
var dataLen = workLens[2];
byte[] Ki;
byte[] Ke;
var constant = new byte[5];
KerberosHash.ConvertToBigEndian((int)usage, constant, 0);
constant[4] = 170;
var encryptor = (AESEncryptor)Encryptor;
Ke = encryptor.DK(key, constant);
constant[4] = 85;
Ki = encryptor.DK(key, constant);
var tmpEnc = new byte[confounderLen + dataLen];
Buffer.BlockCopy(workBuffer, 0, tmpEnc, 0, (confounderLen + dataLen));
var checksum = new byte[checksumLen];
Buffer.BlockCopy(workBuffer, confounderLen + dataLen, checksum, 0, checksumLen);
encryptor.Decrypt(Ke, iv, tmpEnc);
var newChecksum = MakeChecksum(Ki, tmpEnc, checksumLen);
if (!KerberosHash.AreEqualSlow(checksum, newChecksum))
{
throw new SecurityException("Invalid checksum");
}
var data = new byte[dataLen];
Buffer.BlockCopy(tmpEnc, confounderLen, data, 0, dataLen);
return(data);
}
private static byte[] Decrypt(byte[] k1, byte[] ciphertext, KeyUsage keyType)
{
var salt = GetSalt((int)keyType);
var k2 = KerberosHash.HMACMD5(k1, salt);
var checksum = new byte[HashSize];
Buffer.BlockCopy(ciphertext, 0, checksum, 0, HashSize);
var k3 = KerberosHash.HMACMD5(k2, checksum);
var ciphertextOffset = new byte[ciphertext.Length - HashSize];
Buffer.BlockCopy(ciphertext, HashSize, ciphertextOffset, 0, ciphertextOffset.Length);
var plaintext = RC4.Decrypt(k3, ciphertextOffset);
var calculatedHmac = KerberosHash.HMACMD5(k2, plaintext);
var invalidChecksum = false;
if (calculatedHmac.Length >= HashSize)
{
for (var i = 0; i < HashSize; i++)
{
if (calculatedHmac[i] != ciphertext[i])
{
invalidChecksum = true;
}
}
}
if (invalidChecksum)
{
throw new SecurityException("Invalid Checksum");
}
var output = new byte[plaintext.Length - ConfounderSize];
Buffer.BlockCopy(plaintext, ConfounderSize, output, 0, output.Length);
return(output);
}
public byte[] String2Key(KerberosKey key)
{
return(KerberosHash.MD4(key.Password));
}
private static string Hash(string value)
{
var hash = KerberosHash.SHA256(value);
return(ToBase64UrlString(hash));
}
