PRF_BLOCKLEN
l = (dkLen + PRF_BLOCKLEN - 1) / PRF_BLOCKLEN;
*r = emalloc(l * PRF_BLOCKLEN);
prf_iterate(*r + (PRF_BLOCKLEN * i), P, Plen, S, Slen, c,
assert(tmplen == PRF_BLOCKLEN);
(void)memcpy(r, tmp, PRF_BLOCKLEN);
memxor(r, tmp, PRF_BLOCKLEN);
(void)memcpy(data, tmp, PRF_BLOCKLEN);
datalen = PRF_BLOCKLEN;