/// <summary>
/// Transforms the specified region of the data array and copies the resulting transform to the specified region of the destination array.
/// </summary>
/// <param name="data"></param>
/// <param name="dataOffset"></param>
/// <param name="dataCount"></param>
/// <param name="destination"></param>
/// <param name="destinationOffset"></param>
public int TransformBlock(byte[] data, int dataOffset, int dataCount, byte[] destination, int destinationOffset)
{
var dataBuffer = data.AsSpan(dataOffset);
var destinationBuffer = destination.AsSpan(destinationOffset);
var keyStreamBuffer = (Span <byte>) stackalloc byte[ChaCha.BlockLength];
var keyStreamPosition = m_iv;
var numBytesTransformed = 0;
while (ChaCha.BlockLength <= dataCount)
{
var destinationBufferSlice = destinationBuffer.Slice(numBytesTransformed, ChaCha.BlockLength);
dataBuffer.Slice(numBytesTransformed, ChaCha.BlockLength).CopyTo(destinationBufferSlice);
ChaCha.WriteKeyStreamBlock(m_state, checked (keyStreamPosition++), m_numRounds, keyStreamBuffer);
Operations.Xor(keyStreamBuffer, destinationBufferSlice);
dataCount -= ChaCha.BlockLength;
numBytesTransformed += ChaCha.BlockLength;
}
if (0 < dataCount)
{
var destinationBufferSlice = destinationBuffer.Slice(numBytesTransformed, dataCount);
dataBuffer.Slice(numBytesTransformed, dataCount).CopyTo(destinationBufferSlice);
ChaCha.WriteKeyStreamBlock(m_state, checked (keyStreamPosition++), m_numRounds, keyStreamBuffer);
Operations.Xor(keyStreamBuffer.Slice(0, dataCount), destinationBufferSlice);
numBytesTransformed += dataCount;
}
m_iv = keyStreamPosition;
return(numBytesTransformed);
}
/// <summary>
/// Initializes a new instance of the <see cref="AeadChaCha20Poly1305"/> class.
/// </summary>
/// <param name="key">The secret that will be used during initialization.</param>
/// <param name="nonce">The one-time use state parameter.</param>
/// <param name="aad">The arbitrary length additional authenticated data parameter.</param>
public AeadChaCha20Poly1305(ReadOnlySpan <byte> key, ReadOnlySpan <byte> nonce, ReadOnlySpan <byte> aad)
{
var ivLow = 0U;
var ivHigh = BinaryPrimitives.ReadUInt32LittleEndian(nonce);
var oneTimeKey = new byte[64];
ChaCha.WriteKeyStreamBlock(ChaCha.Initialize(key, nonce, ivLow), Operations.ConcatBits(ivHigh, ivLow), 20U, oneTimeKey);
m_aad = aad.ToArray();
m_chaCha20 = ChaCha20.New(key, nonce, 1U);
m_poly1305 = Poly1305.New(oneTimeKey.AsSpan(0, 32).ToArray());
}
