public AEADResult EncryptFinal(AEADResult previousResult)
{
var output = previousResult.RemainingOutput;
if (_bufferOffset != 0)
{
output = EncryptBlock(output);
}
var tagCiphertextPaddingLength = (16 - (int)(_cSize / 8) % 16) % 16;
_tagHash.Update(new byte[tagCiphertextPaddingLength]);
_tagHash.Update(EndianBitConverter.Big.GetBytes(_aSize));
_tagHash.Update(EndianBitConverter.Big.GetBytes(_cSize));
var ctr = new CTRBlockCipher(_cipher);
ctr.Init(new IVParameter(new NullCipherParameter(), _j0));
var blockResult = ctr.EncryptBlock(_tagHash.DigestBuffer(), output);
output = blockResult.RemainingOutput;
return(new AEADResult(previousResult.RemainingInput, output));
}
private Span <byte> EncryptBlock(Span <byte> output)
{
var bufferLength = _bufferOffset;
// encrypt block
var ciphertext = new byte[_blockSize];
_ctr.EncryptBlock(_buffer, ciphertext);
// copy to output
ciphertext.AsSpan().Slice(0, bufferLength).CopyTo(output);
// update tag hash
_tagHash.Update(output.Slice(0, bufferLength));
_cSize += bufferLength * 8;
// clear buffer
_bufferOffset = 0;
Array.Clear(_buffer, 0, _blockSize);
return(output.Slice(bufferLength));
}
public AEADResult DecryptFinal(AEADResult previousResult)
{
// TODO SecurityAssert.AssertBuffer(input, inputOffset, _bufferOffset + TagLength);
// TODO SecurityAssert.AssertBuffer(output, outputOffset, _bufferOffset);
// Consume everything but the Tag
previousResult = Decrypt(previousResult.RemainingInput, previousResult.RemainingOutput);
var input = previousResult.RemainingInput;
var output = previousResult.RemainingOutput;
if (_bufferOffset != 0)
{
output = DecryptBlock(output);
}
var tagCiphertextPaddingLength = (16 - (int)(_cSize / 8) % 16) % 16;
_tagHash.Update(new byte[tagCiphertextPaddingLength]);
_tagHash.Update(EndianBitConverter.Big.GetBytes(_aSize));
_tagHash.Update(EndianBitConverter.Big.GetBytes(_cSize));
var tagCtr = new CTRBlockCipher(_cipher);
tagCtr.Init(new IVParameter(new NullCipherParameter(), _j0));
var digest = _tagHash.DigestBuffer();
var calculatedTag = new byte[16];
tagCtr.EncryptBlock(digest, calculatedTag);
var tag = input.Slice(0, _tagSize).ToArray();
SecurityAssert.AssertHash(calculatedTag, tag);
return(new AEADResult(input.Slice(_tagSize), output));
}
