private byte[] ValidatePassword(byte[] paddedPassword, byte[] password, byte [] uValue)
{
byte[] key = new byte[Constants.KeySize];
byte[] iv = new byte[Constants.VectorSize];
byte[] E16 = new byte[16];
byte[] array = null;
byte[] E = null;
byte[] K1 = null;
int idx = 0;
//Take the SHA - 256 hash of the original input to the algorithm
//and name the resulting 32 bytes, K.
byte[] K = sha256.ComputeHash(paddedPassword, 0, paddedPassword.Length);
//The conditional-OR operator (||) performs a logical - OR
//of its bool operands. If the first operand evaluates to true,
//the second operand isn't evaluated. If the first operand evaluates
//to false, the second operator determines whether the OR expression
//as a whole evaluates to true or false.
while (idx < 64 || E[E.Length - 1] + 32 > idx)
{
Array.Copy(K, key, key.Length);
Array.Copy(K, 16, iv, 0, iv.Length);
//Make a new string, K1, consisting of 64 repetitions of the sequence:
//input password, K, the 48 - byte user key. The 48 byte user key is
//only used when checking the owner password or creating the owner key.If
//checking the user password or creating the user key, K1 is the
//concatenation of the input password and K.
K1 = new byte[(password.Length + K.Length + uValue.Length) * 64];
array = arrayMath.ConcatByteArrays(password, K);
array = arrayMath.ConcatByteArrays(array, uValue);
for (int j = 0, pos = 0; j < 64; j++, pos += array.Length)
{
Array.Copy(array, 0, K1, pos, array.Length);
}
//Encrypt K1 with the AES-128(CBC, no padding) algorithm,
//using the first 16 bytes of K as the key and the second 16 bytes of
//K as the initialization vector. The result of this encryption is E.
E = aes.CreateEncryptor(key, iv).TransformFinalBlock(K1, 0, K1.Length);
//Now we have to take the first 16 bytes of an unsigned big endian integer...
//and compute the remainder modulo 3. Taking the first 16 bytes of E
//as an unsigned big-endian integer, compute the remainder, modulo 3.
Array.Copy(E, E16, E16.Length);
BigInteger bigInteger = new BigInteger(E16.Reverse().Concat(new byte[] { 0x00 }).ToArray());
byte[] result = BigInteger.Remainder(bigInteger, 3).ToByteArray();
switch (result[0])
{
case 0x00:
K = sha256.ComputeHash(E, 0, E.Length);
break;
case 0x01:
K = sha384.ComputeHash(E, 0, E.Length);
break;
case 0x02:
K = sha512.ComputeHash(E, 0, E.Length);
break;
default:
throw new Exception("Unexpected result while computing the remainder, modulo 3.");
}
idx++;
}
return(K);
}
