Function sha_mix_in_key

connectd/handshake.c:212–221

h = SHA-256(h || pub.serializeCompressed()) */

/* h = SHA-256(h || pub.serializeCompressed()) */
static void sha_mix_in_key(struct sha256 *h, const struct pubkey *key)
{
	u8 der[PUBKEY_CMPR_LEN];
	size_t len = sizeof(der);

	secp256k1_ec_pubkey_serialize(secp256k1_ctx, der, &len, &key->pubkey,
				      SECP256K1_EC_COMPRESSED);
	assert(len == sizeof(der));
	sha_mix_in(h, der, sizeof(der));
}

/* out1, out2 = HKDF(in1, in2)` */
static void hkdf_two_keys(struct secret *out1, struct secret *out2,