HMAC_IPAD_VAL
hmac_key[i] = key[i] ^ HMAC_IPAD_VAL;
hmac_key[i] = 0 ^ HMAC_IPAD_VAL;
s->hmac.ipad[i] ^= HMAC_IPAD_VAL;
hmac_init_pad(axf, key, klen, auth_ctx, HMAC_IPAD_VAL);