public override bool VerifyPassword(string password)
{
byte[] secretKey;
using (var hashAlgorithm = CryptoHelpers.Create(PasswordHashAlgorithm))
secretKey = HashPassword(password, PasswordSaltValue, hashAlgorithm, PasswordSpinCount);
var inputBlockKey = CryptoHelpers.HashBytes(
CryptoHelpers.Combine(secretKey, new byte[] { 0xfe, 0xa7, 0xd2, 0x76, 0x3b, 0x4b, 0x9e, 0x79 }),
PasswordHashAlgorithm);
Array.Resize(ref inputBlockKey, PasswordKeyBits / 8);
var valueBlockKey = CryptoHelpers.HashBytes(
CryptoHelpers.Combine(secretKey, new byte[] { 0xd7, 0xaa, 0x0f, 0x6d, 0x30, 0x61, 0x34, 0x4e }),
PasswordHashAlgorithm);
Array.Resize(ref valueBlockKey, PasswordKeyBits / 8);
using (var cipher = CryptoHelpers.CreateCipher(PasswordCipherAlgorithm, PasswordKeyBits, PasswordBlockSize * 8, PasswordCipherChaining))
{
var decryptedVerifier = CryptoHelpers.DecryptBytes(cipher, PasswordEncryptedVerifierHashInput, inputBlockKey, PasswordSaltValue);
var decryptedVerifierHash = CryptoHelpers.DecryptBytes(cipher, PasswordEncryptedVerifierHashValue, valueBlockKey, PasswordSaltValue);
var verifierHash = CryptoHelpers.HashBytes(decryptedVerifier, PasswordHashAlgorithm);
for (var i = 0; i < Math.Min(decryptedVerifierHash.Length, verifierHash.Length); ++i)
{
if (decryptedVerifierHash[i] != verifierHash[i])
{
return(false);
}
}
return(true);
}
}
private static byte[] GenerateSecretKey(string password, byte[] saltValue, HashIdentifier hashIdentifier, byte[] encryptedKeyValue, int spinCount, int keyBits, SymmetricAlgorithm cipher)
{
var block3 = new byte[] { 0x14, 0x6e, 0x0b, 0xe7, 0xab, 0xac, 0xd0, 0xd6 };
byte[] hash;
using (var hashAlgorithm = CryptoHelpers.Create(hashIdentifier))
{
hash = HashPassword(password, saltValue, hashAlgorithm, spinCount);
hash = CryptoHelpers.HashBytes(CryptoHelpers.Combine(hash, block3), hashIdentifier);
}
// Truncate or pad with 0x36
var hashSize = hash.Length;
Array.Resize(ref hash, keyBits / 8);
for (var i = hashSize; i < keyBits / 8; i++)
{
hash[i] = 0x36;
}
// NOTE: the stored salt is padded to a multiple of the block size which affects AES-192
var decryptedKeyValue = CryptoHelpers.DecryptBytes(cipher, encryptedKeyValue, hash, saltValue);
Array.Resize(ref decryptedKeyValue, keyBits / 8);
return(decryptedKeyValue);
}
/// <summary>
/// 2.3.4.7 ECMA-376 Document Encryption Key Generation (Standard Encryption)
/// </summary>
private static byte[] GenerateEcma376SecretKey(string password, byte[] saltValue, HashIdentifier hashIdentifier, int keySize, int verifierHashSize)
{
byte[] hash;
using (var hashAlgorithm = CryptoHelpers.Create(hashIdentifier))
{
hash = hashAlgorithm.ComputeHash(CryptoHelpers.Combine(saltValue, System.Text.Encoding.Unicode.GetBytes(password)));
for (int i = 0; i < 50000; i++)
{
hash = hashAlgorithm.ComputeHash(CryptoHelpers.Combine(BitConverter.GetBytes(i), hash));
}
hash = hashAlgorithm.ComputeHash(CryptoHelpers.Combine(hash, BitConverter.GetBytes(0)));
// The algorithm in this 'DeriveKey' function is the bit that's not clear from the documentation
hash = DeriveKey(hash, hashAlgorithm, keySize, verifierHashSize);
}
Array.Resize(ref hash, keySize / 8);
return(hash);
}
