/// <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);
}
public override SymmetricAlgorithm CreateCipher()
{
return(CryptoHelpers.CreateCipher(CipherAlgorithm, KeyBits, BlockSize * 8, CipherChaining));
}
public override byte[] GenerateBlockKey(int blockNumber, byte[] secretKey)
{
var salt = CryptoHelpers.Combine(secretKey, BitConverter.GetBytes(blockNumber));
return(CryptoHelpers.HashBytes(salt, HashIdentifier.MD5));
}
public override SymmetricAlgorithm CreateCipher()
{
return(CryptoHelpers.CreateCipher(CipherIdentifier.RC4, 0, 0, 0));
}
/// <summary>
/// 2.3.5.2 RC4 CryptoAPI Encryption Key Generation
/// </summary>
private static byte[] GenerateCryptoApiSecretKey(string password, byte[] saltValue, HashIdentifier hashAlgorithm, int keySize)
{
return(CryptoHelpers.HashBytes(CryptoHelpers.Combine(saltValue, System.Text.Encoding.Unicode.GetBytes(password)), hashAlgorithm));
}
public override SymmetricAlgorithm CreateCipher()
{
return(CryptoHelpers.CreateCipher(CipherAlgorithm, KeySize, BlockSize, CipherMode.ECB));
}