public int DecryptFinal(byte[] input, int inputOffset, byte[] output, int outputOffset)
{
SecurityBufferAssert.AssertBuffer(input, inputOffset, TagLength);
SecurityBufferAssert.AssertBuffer(output, outputOffset, bufferOffset);
var total = 0;
if (bufferOffset != 0)
{
total += bufferOffset;
inputOffset += bufferOffset;
DecryptBlock(output, outputOffset);
}
var tagCiphertextPaddingLength = (16 - (int)(cSize / 8) % 16) % 16;
tagHash.Update(new byte[tagCiphertextPaddingLength], 0, tagCiphertextPaddingLength);
tagHash.Update(EndianBitConverter.Big.GetBytes(aSize), 0, sizeof(long));
tagHash.Update(EndianBitConverter.Big.GetBytes(cSize), 0, sizeof(long));
var ctr = new CTRBlockCipher(Cipher);
ctr.Init(new IVParameter(null, j0));
var calculatedTag = new byte[16];
ctr.EncryptBlock(tagHash.Digest(), 0, calculatedTag, 0);
var tag = new byte[16];
Array.Copy(input, inputOffset, tag, 0, TagLength);
SecurityAssert.HashAssert(calculatedTag, tag);
return total;
}
public void Init(ICipherParameters parameters)
{
// setup AAD
var aadParam = parameters as AADParameter;
SecurityAssert.NotNull(aadParam);
var a = aadParam.AAD;
aSize = a.Length * 8;
// setup IV
var ivParam = aadParam.Parameters as IVParameter;
SecurityAssert.NotNull(ivParam);
var iv = ivParam.IV;
ivSize = iv.Length * 8;
// setup cipher
Cipher.Init(ivParam.Parameters);
// setup H subkey
h = new byte[16];
Cipher.EncryptBlock(new byte[16], 0, h, 0);
// setup tag hash
tagHash = new GHash(h);
tagHash.Update(a, 0, a.Length);
var tagAADPaddingLength = 16 - a.Length % 16;
tagHash.Update(new byte[tagAADPaddingLength], 0, tagAADPaddingLength);
// setup pre-counter block
if (iv.Length == 12)
{
// IV || 0^31 ||1
j0 = new byte[16];
Array.Copy(iv, j0, 12);
j0[15] = 1;
}
else
{
// GHASH_H(IV || 0^(s+64) || [len(IV)])
var j0PaddingLength = 8 + (16 - iv.Length % 16) % 16;
var j0Hash = new GHash(h);
j0Hash.Update(iv, 0, iv.Length);
j0Hash.Update(new byte[j0PaddingLength], 0, j0PaddingLength);
j0Hash.Update(EndianBitConverter.Big.GetBytes(ivSize), 0, sizeof(long));
j0 = j0Hash.Digest();
}
ctr = new CTRBlockCipher(Cipher);
ctr.Init(new IVParameter(null, j0));
ctr.Inc();
cSize = 0;
}
public int EncryptFinal(byte[] output, int offset)
{
var total = 0;
if (bufferOffset != 0)
{
var len = bufferOffset;
EncryptBlock(output, offset);
total += len;
offset += len;
}
var tagCiphertextPaddingLength = (16 - (int)(cSize / 8) % 16) % 16;
tagHash.Update(new byte[tagCiphertextPaddingLength], 0, tagCiphertextPaddingLength);
tagHash.Update(EndianBitConverter.Big.GetBytes(aSize), 0, sizeof(long));
tagHash.Update(EndianBitConverter.Big.GetBytes(cSize), 0, sizeof(long));
var ctr = new CTRBlockCipher(Cipher);
ctr.Init(new IVParameter(null, j0));
ctr.EncryptBlock(tagHash.Digest(), 0, output, offset);
total += BlockLength;
return total;
}
