/*
* This function computes Phash with the specified HMAC
* engine, XORing the output with the current contents of
* the outBuf[] buffer.
*/
static void Phash(HMAC hm, byte[] s, int soff, int slen,
byte[] bufa, byte[] bufb,
byte[] label, byte[] seed,
byte[] outBuf, int outOff, int outLen)
{
/*
* Set the key for HMAC.
*/
hm.SetKey(s, soff, slen);
/*
* Compute A(1) = HMAC(secret, seed).
*/
hm.Update(label);
hm.Update(seed);
hm.DoFinal(bufa, 0);
while (outLen > 0)
{
/*
* Next chunk: HMAC(secret, A(i) + label + seed)
*/
hm.Update(bufa);
hm.Update(label);
hm.Update(seed);
hm.DoFinal(bufb, 0);
int clen = Math.Min(hm.MACSize, outLen);
for (int i = 0; i < clen; i++)
{
outBuf[outOff++] ^= bufb[i];
}
outLen -= clen;
/*
* If we are not finished, then compute:
* A(i+1) = HMAC(secret, A(i))
*/
if (outLen > 0)
{
hm.Update(bufa);
hm.DoFinal(bufa, 0);
}
}
}
