HMAC_IPAD
ipad[i] = (i < klen ? k[i] : 0) ^ HMAC_IPAD;
memset( k_ipad, HMAC_IPAD, sizeof k_ipad);
hkey->hk_ipad[i] ^= HMAC_IPAD;
key[key_len] = hkey->hk_ipad[key_len] ^ HMAC_IPAD;
out_str[i] = hkey->hk_ipad[i] ^ HMAC_IPAD;
ipad[i] = (key8[i] ^ HMAC_IPAD);
ipad[i] = HMAC_IPAD;