/// <summary>
/// Decrypts the inner stream and populates <paramref name="destination"/> with the resulting plaintext.
/// </summary>
/// <param name="destination">The buffer where the plaintext will be output to.</param>
/// <param name="additionalData">Additional data to use when verify the authentication tag.</param>
/// <returns>The number of bytes written to <paramref name="destination"/>.</returns>
public int Read(Span <byte> destination, ReadOnlySpan <byte> additionalData)
{
var inputSize = CalculateCiphertextLength(destination.Length);
using (var ciphertextBuffer = new RentedArray(inputSize))
{
if (!this.CanRead)
{
throw new NotSupportedException();
}
var bytesRead = this.stream.Read(ciphertextBuffer.AsSpan());
var decryptResult = crypto_secretstream_xchacha20poly1305_pull(
this.state.Handle,
ref MemoryMarshal.GetReference(destination),
out var decryptedBlockLongLength,
out var tag,
in MemoryMarshal.GetReference(ciphertextBuffer.AsReadOnlySpan()),
(UInt64)bytesRead,
ref MemoryMarshal.GetReference(additionalData),
(UInt64)additionalData.Length);
if (decryptResult != 0)
{
throw new CryptographicException("block is invalid or corrupt");
}
this.tagOfLastDecryptedBlock = tag;
return((int)decryptedBlockLongLength);
}
}
private void EncryptBlock(ReadOnlySpan <byte> source, ReadOnlySpan <byte> additionalData, byte tag)
{
if (!this.CanWrite)
{
throw new NotSupportedException();
}
if (!this.headerWritten)
{
this.WriteHeader();
}
var count = source.Length;
if (count > 0)
{
var outputSize = CalculateCiphertextLength(count);
using (var ciphertextBuffer = new RentedArray(outputSize))
{
var encryptionResult = crypto_secretstream_xchacha20poly1305_push(
this.state.Handle,
ref MemoryMarshal.GetReference(ciphertextBuffer.AsSpan()),
out var ciphertextLength,
in MemoryMarshal.GetReference(source),
(ulong)count,
ref MemoryMarshal.GetReference(additionalData),
(UInt64)additionalData.Length,
tag);
if (encryptionResult != 0)
{
throw new CryptographicException("encryption of block failed");
}
this.stream.Write(ciphertextBuffer.AsReadOnlySpan(0, (int)ciphertextLength));
}
}
}
