krb5_c_prfplus
ret = krb5_c_prfplus(context, k, input, &rnd);
ret = krb5_c_prfplus(context, k1, &pepper1_data, &prf1);
ret = krb5_c_prfplus(context, k2, &pepper2_data, &prf2);
ret = krb5_c_prfplus(context, ikey, &prf_input, &wbytes);