cx->hashobj->update(cx->hash, cx->ipad, sizeof(cx->ipad));
cx->hashobj->update(cx->hash, cx->ipad, cx->hashobj->blocklength);
HMAC_Begin(HMACContext *cx){    /* start inner hash */    cx->hashobj->begin(cx->hash);    cx->hashobj->update(cx->hash, cx->ipad, sizeof(cx->ipad));}