CURVE25519_SIZE
extern int crypto_scalarmult_curve25519(uint8_t [CURVE25519_SIZE],
const uint8_t [CURVE25519_SIZE], const uint8_t [CURVE25519_SIZE]);
gen_pubkey(uint8_t key[CURVE25519_SIZE], uint8_t pubkey[CURVE25519_SIZE])
static const uint8_t basepoint[CURVE25519_SIZE] = {9};