/// <summary>
/// Initializes a new instance of the <see cref="SymmetricDecryptStream" /> class.
/// </summary>
/// <param name="stream">
/// The inner <see cref="Stream" /> to read the encrypted message from.
/// </param>
/// <param name="settings">
/// The <see cref="SymmetricDecryptionSettings" /> specifying the cryptographic algorithm settings.
/// </param>
/// <param name="keyIdentifier">
/// The key identifier to retrieve the encryption key.
/// </param>
public SymmetricDecryptStream(
Stream stream,
SymmetricDecryptionSettings settings,
string?keyIdentifier = null)
{
Check.NotNull(stream, nameof(stream));
Check.NotNull(settings, nameof(settings));
_cryptoTransform = CreateCryptoTransform(settings, stream, keyIdentifier);
_cryptoStream = new CryptoStream(stream, _cryptoTransform, CryptoStreamMode.Read);
}
private static ICryptoTransform CreateCryptoTransform(
SymmetricDecryptionSettings settings,
Stream stream,
string?keyIdentifier)
{
Check.NotNull(settings, nameof(settings));
Check.NotNull(stream, nameof(stream));
byte[]? encryptionKey = settings.KeyProvider != null
? settings.KeyProvider(keyIdentifier)
: settings.Key;
using var algorithm =
SymmetricAlgorithmFactory.CreateSymmetricAlgorithm(settings, encryptionKey);
if (settings.InitializationVector != null)
{
return(algorithm.CreateDecryptor());
}
// Read the IV prepended to the message
byte[] buffer = new byte[algorithm.IV.Length];
var totalReadCount = 0;
while (totalReadCount < algorithm.IV.Length)
{
int readCount = stream.Read(buffer, totalReadCount, algorithm.IV.Length - totalReadCount);
if (readCount == 0)
{
break;
}
totalReadCount += readCount;
}
algorithm.IV = buffer;
return(algorithm.CreateDecryptor());
}
