bitcoin/script: add internal hash160_key helper.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

bitcoin/script.c

@@ -47,6 +47,13 @@ static void hash160(struct ripemd160 *redeemhash, const void *mem, size_t len)
 	ripemd160(redeemhash, h.u.u8, sizeof(h));
 }
 
+static void hash160_key(struct ripemd160 *khash, const struct pubkey *key)
+{
+	u8 der[PUBKEY_DER_LEN];
+	pubkey_to_der(der, key);
+	hash160(khash, der, sizeof(der));
+}
+
 static void add(u8 **scriptp, const void *mem, size_t len)
 {
 	size_t oldlen = tal_count(*scriptp);
@@ -218,11 +225,9 @@ u8 *scriptpubkey_p2sh(const tal_t *ctx, const u8 *redeemscript)
 u8 *scriptpubkey_p2pkh(const tal_t *ctx, const struct pubkey *pubkey)
 {
 	struct bitcoin_address addr;
-	u8 der[PUBKEY_DER_LEN];
 	u8 *script = tal_arr(ctx, u8, 0);
 
-	pubkey_to_der(der, pubkey);
-	hash160(&addr.addr, der, sizeof(der));
+	hash160_key(&addr.addr, pubkey);
 	add_op(&script, OP_DUP);
 	add_op(&script, OP_HASH160);
 	add_push_bytes(&script, &addr.addr, sizeof(addr.addr));
@@ -247,14 +252,12 @@ u8 *bitcoin_redeem_p2pkh(const tal_t *ctx, const struct pubkey *pubkey,
 u8 *bitcoin_redeem_p2sh_p2wpkh(const tal_t *ctx, const struct pubkey *key)
 {
 	struct ripemd160 keyhash;
-	u8 der[PUBKEY_DER_LEN];
 	u8 *script = tal_arr(ctx, u8, 0);
 
 	/* BIP141: BIP16 redeemScript pushed in the scriptSig is exactly a
 	 * push of a version byte plus a push of a witness program. */
 	add_number(&script, 0);
-	pubkey_to_der(der, key);
-	hash160(&keyhash, der, sizeof(der));
+	hash160_key(&keyhash, key);
 	add_push_bytes(&script, &keyhash, sizeof(keyhash));
 	return script;
 }
@@ -319,12 +322,10 @@ u8 *scriptpubkey_p2wsh(const tal_t *ctx, const u8 *witnessscript)
 u8 *scriptpubkey_p2wpkh(const tal_t *ctx, const struct pubkey *key)
 {
 	struct ripemd160 h;
-	u8 der[PUBKEY_DER_LEN];
 	u8 *script = tal_arr(ctx, u8, 0);
 
 	add_op(&script, OP_0);
-	pubkey_to_der(der, key);
-	hash160(&h, der, sizeof(der));
+	hash160_key(&h, key);
 	add_push_bytes(&script, &h, sizeof(h));
 	return script;
 }
@@ -479,14 +480,10 @@ u8 *bitcoin_redeem_htlc_recv(const tal_t *ctx,
 /* Create scriptcode (fake witness, basically) for P2WPKH */
 u8 *p2wpkh_scriptcode(const tal_t *ctx, const struct pubkey *key)
 {
-	struct sha256 h;
 	struct ripemd160 pkhash;
-	u8 der[PUBKEY_DER_LEN];
 	u8 *script = tal_arr(ctx, u8, 0);
 
-	pubkey_to_der(der, key);
-	sha256(&h, der, sizeof(der));
-	ripemd160(&pkhash, h.u.u8, sizeof(h));
+	hash160_key(&pkhash, key);
 	/* BIP143:
 	 *
 	 * For P2WPKH witness program, the scriptCode is