public void Init(ICipherParameters parameters)
{
// setup AAD
var aadParam = parameters as AADParameter;
SecurityAssert.NotNull(aadParam);
var a = aadParam !.AAD;
var aSize = a.Length * 8;
// setup IV
var ivParam = aadParam !.Parameters as IVParameter;
SecurityAssert.NotNull(ivParam);
var iv = ivParam !.IV;
var ivSize = iv.Length * 8;
// setup cipher
_cipher.Init(ivParam !.Parameters);
// setup H subkey
var h = new byte[16];
_cipher.EncryptBlock(new byte[16], 0, h, 0);
// setup tag hash
var tagHash = new GHash(h);
tagHash.Update(a);
var tagAADPaddingLength = 16 - a.Length % 16;
tagHash.Update(new byte[tagAADPaddingLength]);
// setup pre-counter block
byte[] j0;
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);
j0Hash.Update(new byte[j0PaddingLength]);
j0Hash.Update(EndianBitConverter.Big.GetBytes((long)ivSize));
j0 = j0Hash.DigestBuffer();
}
var ctr = new CTRBlockCipher(_cipher);
ctr.Init(new IVParameter(j0));
ctr.Inc();
_state = new State(aSize, BlockLength, TagLength, j0, tagHash, ctr, _cipher);
}
