private void ReadFrom(Stream s, string password)
{
byte[] format = new byte[2];
s.Read(format, 0, 2);
if (Encoding.ASCII.GetString(format) != "CC")
{
throw new InvalidCryptoContainerException("Invalid CryptoContainer format.");
}
switch (s.ReadByte()) //version
{
case 0:
ReadPlainTextFrom(s);
break;
case 1: //depricated version
{
if (password == null)
{
throw new InvalidCryptoContainerException("Password required.");
}
//CryptoAlgo
SymmetricEncryptionAlgorithm cryptoAlgo = (SymmetricEncryptionAlgorithm)s.ReadByte();
//KeySizeBytes
int keySizeBytes = s.ReadByte();
byte[] IV = new byte[s.ReadByte()];
s.Read(IV, 0, IV.Length);
byte[] key;
switch (keySizeBytes)
{
case 16:
key = HashAlgorithm.Create("MD5").ComputeHash(Encoding.UTF8.GetBytes(password));
break;
case 32:
key = HashAlgorithm.Create("SHA256").ComputeHash(Encoding.UTF8.GetBytes(password));
break;
default:
throw new CryptoException("CryptoContainer key size not supported.");
}
_containerKey = new SymmetricCryptoKey(cryptoAlgo, key, IV);
ReadPlainTextFrom(_containerKey.GetCryptoStreamReader(s));
//auto upgrade to version 2 with PBKDF2-HMAC-SHA256 when calling WriteTo
_kdf = PBKDF2.CreateHMACSHA256(password, keySizeBytes, PBKDF2_ITERATION_COUNT);
key = _kdf.GetBytes(keySizeBytes);
_containerKey = new SymmetricCryptoKey(cryptoAlgo, key, IV);
_hmac = new HMACSHA256(key);
}
break;
case 2: //using PBKDF2-HMAC-SHA256
{
if (password == null)
{
throw new InvalidCryptoContainerException("Password required.");
}
//CryptoAlgo
SymmetricEncryptionAlgorithm cryptoAlgo = (SymmetricEncryptionAlgorithm)s.ReadByte();
//KeySizeBytes
int keySizeBytes = s.ReadByte();
byte[] IV = new byte[s.ReadByte()];
s.Read(IV, 0, IV.Length);
byte[] salt = new byte[s.ReadByte()];
s.Read(salt, 0, salt.Length);
byte[] HMAC = new byte[s.ReadByte()];
s.Read(HMAC, 0, HMAC.Length);
_kdf = PBKDF2.CreateHMACSHA256(password, salt, PBKDF2_ITERATION_COUNT);
byte[] key = _kdf.GetBytes(keySizeBytes);
//authenticate data
_hmac = new HMACSHA256(key);
long startPosition = s.Position;
byte[] computedHMAC = _hmac.ComputeHash(s);
s.Position = startPosition;
//verify hmac
for (int i = 0; i < HMAC.Length; i++)
{
if (HMAC[i] != computedHMAC[i])
{
throw new CryptoException("Invalid password or data tampered.");
}
}
//decrypt data
_containerKey = new SymmetricCryptoKey(cryptoAlgo, key, IV);
ReadPlainTextFrom(_containerKey.GetCryptoStreamReader(s));
}
break;
case -1:
throw new EndOfStreamException();
default:
throw new InvalidCryptoContainerException("CryptoContainer format version not supported.");
}
}