Function bip86_pubkey

lightningd/hsm_control.c:269–303

Derive BIP86 public key from the base key */

/* Derive BIP86 public key from the base key */
void bip86_pubkey(struct lightningd *ld, struct pubkey *pubkey, u32 index)
{
	const uint32_t flags = BIP32_FLAG_KEY_PUBLIC | BIP32_FLAG_SKIP_HASH;
	struct ext_key ext;
	u32 path[2];

	if (index >= BIP32_INITIAL_HARDENED_CHILD)
		fatal("Can't derive key %u (too large!)", index);

	/* BIP86 path: m/86'/0'/0'/0/index */
	path[0] = 0; /* change (0 for receive) */
	path[1] = index; /* address_index */

	assert(ld->bip86_base != NULL);

	if (bip32_key_from_parent_path(ld->bip86_base, path, 2, flags, &ext) != WALLY_OK)
		fatal("Can't derive key %u", index);

	if (!secp256k1_ec_pubkey_parse(secp256k1_ctx, &pubkey->pubkey,
				       ext.pub_key, sizeof(ext.pub_key)))
		fatal("Can't parse derived key %u", index);

	/* Don't assume hsmd supports it! */
	if (hsm_capable(ld, WIRE_HSMD_CHECK_BIP86_PUBKEY)) {
		bool ok;
		const u8 *msg = towire_hsmd_check_bip86_pubkey(NULL, index, pubkey);
		msg = hsm_sync_req(tmpctx, ld, take(msg));
		if (!fromwire_hsmd_check_bip86_pubkey_reply(msg, &ok))
			fatal("Invalid check_bip86_pubkey_reply from hsm");

		if (!ok)
			fatal("HSM said BIP86 key derivation of %u != %s",
			      index, fmt_pubkey(tmpctx, pubkey));
	}
}

const u8 *hsm_sync_req(const tal_t *ctx, struct lightningd *ld, const u8 *msg)
{