kex_ecdh_dec_key_group
if ((r = kex_ecdh_dec_key_group(kex, client_blob, server_key, group,
r = kex_ecdh_dec_key_group(kex, server_blob, kex->ec_client_key,
kex_ecdh_dec_key_group(struct kex *, const struct sshbuf *, EC_KEY *key,