core-lightning/bitcoin/script.c

#include "address.h"
#include "locktime.h"
#include "preimage.h"
#include "pubkey.h"
#include "script.h"
#include "signature.h"
#include "tx.h"
#include <assert.h>
#include <ccan/crypto/ripemd160/ripemd160.h>
#include <ccan/crypto/sha256/sha256.h>
#include <ccan/endian/endian.h>
#include <ccan/mem/mem.h>

/* Some standard ops */
#define OP_0		0x00
#define OP_PUSHBYTES(val) (val)
#define OP_PUSHDATA1	0x4C
#define OP_PUSHDATA2	0x4D
#define OP_PUSHDATA4	0x4E
#define OP_NOP		0x61
#define OP_IF		0x63
#define OP_NOTIF	0x64
#define OP_ELSE		0x67
#define OP_ENDIF	0x68
#define OP_2DROP	0x6d
#define OP_DEPTH	0x74
#define OP_DROP		0x75
#define OP_DUP		0x76
#define OP_SWAP		0x7c
#define OP_EQUAL	0x87
#define OP_EQUALVERIFY	0x88
#define OP_SIZE		0x82
#define OP_1SUB		0x8C
#define OP_ADD		0x93
#define OP_CHECKSIG	0xAC
#define OP_CHECKMULTISIG	0xAE
#define OP_HASH160	0xA9
#define OP_CHECKSEQUENCEVERIFY	0xB2
#define OP_CHECKLOCKTIMEVERIFY	0xB1

/* Bitcoin's OP_HASH160 is RIPEMD(SHA256()) */
static void hash160(struct ripemd160 *redeemhash, const void *mem, size_t len)
{
	struct sha256 h;

	sha256(&h, mem, len);
	ripemd160(redeemhash, h.u.u8, sizeof(h));
}

static void add(u8 **scriptp, const void *mem, size_t len)
{
	size_t oldlen = tal_count(*scriptp);
	tal_resize(scriptp, oldlen + len);
	memcpy(*scriptp + oldlen, mem, len);
}

static void add_op(u8 **scriptp, u8 op)
{
	add(scriptp, &op, 1);
}

static void add_push_bytes(u8 **scriptp, const void *mem, size_t len)
{
	if (len < 76)
		add_op(scriptp, OP_PUSHBYTES(len));
	else if (len < 256) {
		char c = len;
		add_op(scriptp, OP_PUSHDATA1);
		add(scriptp, &c, 1);
	} else if (len < 65536) {
		le16 v = cpu_to_le16(len);
		add_op(scriptp, OP_PUSHDATA2);
		add(scriptp, &v, 2);
	} else {
		le32 v = cpu_to_le32(len);
		add_op(scriptp, OP_PUSHDATA4);
		add(scriptp, &v, 4);
	}

	add(scriptp, memcheck(mem, len), len);
}

static void add_number(u8 **script, u32 num)
{
	if (num == 0)
		add_op(script, 0);
	else if (num <= 16)
		add_op(script, 0x50 + num);
	else {
		le64 n = cpu_to_le64(num);

		/* Beware: encoding is signed! */
		if (num <= 0x0000007F)
			add_push_bytes(script, &n, 1);
		else if (num <= 0x00007FFF)
			add_push_bytes(script, &n, 2);
		else if (num <= 0x007FFFFF)
			add_push_bytes(script, &n, 3);
		else if (num <= 0x7FFFFFFF)
			add_push_bytes(script, &n, 4);
		else
			add_push_bytes(script, &n, 5);
	}
}

static void add_push_key(u8 **scriptp, const struct pubkey *key)
{
	u8 der[PUBKEY_DER_LEN];
	pubkey_to_der(der, key);

	add_push_bytes(scriptp, der, sizeof(der));
}

static void add_push_sig(u8 **scriptp, const secp256k1_ecdsa_signature *sig)
{
	u8 der[73];
	size_t len = signature_to_der(der, sig);

	/* Append sighash type */
	der[len++] = SIGHASH_ALL;
	add_push_bytes(scriptp, der, len);
}

static u8 *stack_key(const tal_t *ctx, const struct pubkey *key)
{
	u8 der[PUBKEY_DER_LEN];
	pubkey_to_der(der, key);

	return tal_dup_arr(ctx, u8, der, sizeof(der), 0);
}

/* Bitcoin wants DER encoding. */
static u8 *stack_sig(const tal_t *ctx, const secp256k1_ecdsa_signature *sig)
{
	u8 der[73];
	size_t len = signature_to_der(der, sig);

	/* Append sighash type */
	der[len++] = SIGHASH_ALL;
	return tal_dup_arr(ctx, u8, der, len, 0);
}

static u8 *stack_preimage(const tal_t *ctx, const struct preimage *preimage)
{
	return tal_dup_arr(ctx, u8, preimage->r, sizeof(preimage->r), 0);
}

/* Bitcoin script stack values are a special, special snowflake.
 *
 * They're little endian values, but 0 is an empty value.  We only
 * handle single byte values here. */
static u8 *stack_number(const tal_t *ctx, unsigned int num)
{
	u8 val;

	if (num == 0)
		return tal_arr(ctx, u8, 0);

	val = num;
	assert(val == num);

	/* We use tal_dup_arr since we want tal_count() to work */
	return tal_dup_arr(ctx, u8, &val, 1, 0);
}

/* tal_count() gives the length of the script. */
u8 *bitcoin_redeem_2of2(const tal_t *ctx,
			const struct pubkey *key1,
			const struct pubkey *key2)
{
	u8 *script = tal_arr(ctx, u8, 0);
	add_number(&script, 2);
	if (pubkey_cmp(key1, key2) < 0) {
		add_push_key(&script, key1);
		add_push_key(&script, key2);
	} else {
		add_push_key(&script, key2);
		add_push_key(&script, key1);
	}
	add_number(&script, 2);
	add_op(&script, OP_CHECKMULTISIG);
	return script;
}

u8 *scriptpubkey_p2sh_hash(const tal_t *ctx, const struct ripemd160 *redeemhash)
{
	u8 *script = tal_arr(ctx, u8, 0);

	add_op(&script, OP_HASH160);
	add_push_bytes(&script, redeemhash->u.u8, sizeof(redeemhash->u.u8));
	add_op(&script, OP_EQUAL);
	return script;
}

/* Create p2sh for this redeem script. */
u8 *scriptpubkey_p2sh(const tal_t *ctx, const u8 *redeemscript)
{
	struct ripemd160 redeemhash;

	hash160(&redeemhash, redeemscript, tal_count(redeemscript));
	return scriptpubkey_p2sh_hash(ctx, &redeemhash);
}

/* Create an output script using p2pkh */
u8 *scriptpubkey_p2pkh(const tal_t *ctx, const struct bitcoin_address *addr)
{
	u8 *script = tal_arr(ctx, u8, 0);

	add_op(&script, OP_DUP);
	add_op(&script, OP_HASH160);
	add_push_bytes(&script, &addr->addr, sizeof(addr->addr));
	add_op(&script, OP_EQUALVERIFY);
	add_op(&script, OP_CHECKSIG);
	return script;
}

/* Create an input script which spends p2pkh */
u8 *bitcoin_redeem_p2pkh(const tal_t *ctx, const struct pubkey *pubkey,
			 const secp256k1_ecdsa_signature *sig)
{
	u8 *script = tal_arr(ctx, u8, 0);

	add_push_sig(&script, sig);
	add_push_key(&script, pubkey);

	return script;
}

/* Create the redeemscript for a P2SH + P2WPKH (for signing tx) */
u8 *bitcoin_redeem_p2sh_p2wpkh(const tal_t *ctx, const struct pubkey *key)
{
	struct ripemd160 keyhash;
	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_hash160(key, &keyhash);
	add_push_bytes(&script, &keyhash, sizeof(keyhash));
	return script;
}

u8 *bitcoin_scriptsig_p2sh_p2wpkh(const tal_t *ctx, const struct pubkey *key)
{
	u8 *redeemscript = bitcoin_redeem_p2sh_p2wpkh(ctx, key), *script;

	/* BIP141: The scriptSig must be exactly a push of the BIP16
	 * redeemScript or validation fails. */
	script = tal_arr(ctx, u8, 0);
	add_push_bytes(&script, redeemscript, tal_count(redeemscript));
	tal_free(redeemscript);
	return script;
}

/* Create an input which spends the p2sh-p2wpkh. */
void bitcoin_witness_p2sh_p2wpkh(const tal_t *ctx,
				 struct bitcoin_tx_input *input,
				 const secp256k1_ecdsa_signature *sig,
				 const struct pubkey *key)
{
	input->script = bitcoin_scriptsig_p2sh_p2wpkh(ctx, key);
	input->witness = bitcoin_witness_p2wpkh(ctx, sig, key);
}

u8 **bitcoin_witness_p2wpkh(const tal_t *ctx,
			    const secp256k1_ecdsa_signature *sig,
			    const struct pubkey *key)
{
	u8 **witness;

	/* BIP141: The witness must consist of exactly 2 items (≤ 520
	 * bytes each). The first one a signature, and the second one
	 * a public key. */
	witness = tal_arr(ctx, u8 *, 2);
	witness[0] = stack_sig(witness, sig);
	witness[1] = stack_key(witness, key);
	return witness;
}

/* Create an output script for a 32-byte witness. */
u8 *scriptpubkey_p2wsh(const tal_t *ctx, const u8 *witnessscript)
{
	struct sha256 h;
	u8 *script = tal_arr(ctx, u8, 0);

	add_op(&script, OP_0);
	sha256(&h, witnessscript, tal_count(witnessscript));
	add_push_bytes(&script, h.u.u8, sizeof(h.u.u8));
	return script;
}

/* Create an output script for a 20-byte witness. */
u8 *scriptpubkey_p2wpkh(const tal_t *ctx, const struct pubkey *key)
{
	struct ripemd160 h;
	u8 *script = tal_arr(ctx, u8, 0);

	add_op(&script, OP_0);
	pubkey_to_hash160(key, &h);
	add_push_bytes(&script, &h, sizeof(h));
	return script;
}

u8 *scriptpubkey_p2wpkh_derkey(const tal_t *ctx, const u8 der[33])
{
	u8 *script = tal_arr(ctx, u8, 0);
	struct ripemd160 h;

	add_op(&script, OP_0);
	hash160(&h, der, PUBKEY_DER_LEN);
	add_push_bytes(&script, &h, sizeof(h));
	return script;
}

u8 *scriptpubkey_witness_raw(const tal_t *ctx, u8 version,
			     const u8 *wprog, size_t wprog_size)
{
	u8 *script = tal_arr(ctx, u8, 0);
	add_number(&script, version);
	add_push_bytes(&script, wprog, wprog_size);
	return script;
}

/* Create a witness which spends the 2of2. */
u8 **bitcoin_witness_2of2(const tal_t *ctx,
			  const secp256k1_ecdsa_signature *sig1,
			  const secp256k1_ecdsa_signature *sig2,
			  const struct pubkey *key1,
			  const struct pubkey *key2)
{
	u8 **witness = tal_arr(ctx, u8 *, 4);

	/* OP_CHECKMULTISIG has an out-by-one bug, which MBZ */
	witness[0] = stack_number(witness, 0);

	/* sig order should match key order. */
	if (pubkey_cmp(key1, key2) < 0) {
		witness[1] = stack_sig(witness, sig1);
		witness[2] = stack_sig(witness, sig2);
	} else {
		witness[1] = stack_sig(witness, sig2);
		witness[2] = stack_sig(witness, sig1);
	}

	witness[3] = bitcoin_redeem_2of2(witness, key1, key2);
	return witness;
}

/* Create scriptcode (fake witness, basically) for P2WPKH */
u8 *p2wpkh_scriptcode(const tal_t *ctx, const struct pubkey *key)
{
	struct ripemd160 pkhash;
	u8 *script = tal_arr(ctx, u8, 0);
	pubkey_to_hash160(key, &pkhash);

	/* BIP143:
	 *
	 * For P2WPKH witness program, the scriptCode is
	 * 0x1976a914{20-byte-pubkey-hash}88ac.
	 */

	/* PUSH(25): OP_DUP OP_HASH160 PUSH(20) 20-byte-pubkey-hash
	 * OP_EQUALVERIFY OP_CHECKSIG */
	add_op(&script, OP_DUP);
	add_op(&script, OP_HASH160);
	add_push_bytes(&script, &pkhash, sizeof(pkhash));
	add_op(&script, OP_EQUALVERIFY);
	add_op(&script, OP_CHECKSIG);

	return script;
}

bool is_p2pkh(const u8 *script, struct bitcoin_address *addr)
{
	size_t script_len = tal_len(script);

	if (script_len != BITCOIN_SCRIPTPUBKEY_P2PKH_LEN)
		return false;
	if (script[0] != OP_DUP)
		return false;
	if (script[1] != OP_HASH160)
		return false;
	if (script[2] != OP_PUSHBYTES(20))
		return false;
	if (script[23] != OP_EQUALVERIFY)
		return false;
	if (script[24] != OP_CHECKSIG)
		return false;
	if (addr)
		memcpy(addr, script+3, 20);
	return true;
}

bool is_p2sh(const u8 *script, struct ripemd160 *addr)
{
	size_t script_len = tal_len(script);

	if (script_len != BITCOIN_SCRIPTPUBKEY_P2SH_LEN)
		return false;
	if (script[0] != OP_HASH160)
		return false;
	if (script[1] != OP_PUSHBYTES(20))
		return false;
	if (script[22] != OP_EQUAL)
		return false;
	if (addr)
		memcpy(addr, script+2, 20);
	return true;
}

bool is_p2wsh(const u8 *script, struct sha256 *addr)
{
	size_t script_len = tal_len(script);

	if (script_len != BITCOIN_SCRIPTPUBKEY_P2WSH_LEN)
		return false;
	if (script[0] != OP_0)
		return false;
	if (script[1] != OP_PUSHBYTES(sizeof(struct sha256)))
		return false;
	if (addr)
		memcpy(addr, script+2, sizeof(struct sha256));
	return true;
}

bool is_p2wpkh(const u8 *script, struct bitcoin_address *addr)
{
	size_t script_len = tal_len(script);

	if (script_len != BITCOIN_SCRIPTPUBKEY_P2WPKH_LEN)
		return false;
	if (script[0] != OP_0)
		return false;
	if (script[1] != OP_PUSHBYTES(sizeof(struct ripemd160)))
		return false;
	if (addr)
		memcpy(addr, script+2, sizeof(*addr));
	return true;
}

u8 **bitcoin_witness_sig_and_element(const tal_t *ctx,
				     const secp256k1_ecdsa_signature *sig,
				     const void *elem, size_t elemsize,
				     const u8 *witnessscript)
{
	u8 **witness = tal_arr(ctx, u8 *, 3);

	witness[0] = stack_sig(witness, sig);
	witness[1] = tal_dup_arr(witness, u8, elem, elemsize, 0);
	witness[2] = tal_dup_arr(witness, u8,
				 witnessscript, tal_count(witnessscript), 0);

	return witness;
}

/* BOLT #3:
 *
 * This output sends funds back to the owner of this commitment transaction,
 * thus must be timelocked using `OP_CSV`. It can be claimed, without delay,
 * by the other party if they know the revocation key. The output is a version
 * 0 P2WSH, with a witness script:
 *
 *     OP_IF
 *         # Penalty transaction
 *         <revocationkey>
 *     OP_ELSE
 *         `to_self_delay`
 *         OP_CSV
 *         OP_DROP
 *         <local_delayedkey>
 *     OP_ENDIF
 *     OP_CHECKSIG
 */
u8 *bitcoin_wscript_to_local(const tal_t *ctx, u16 to_self_delay,
			     const struct pubkey *revocation_pubkey,
			     const struct pubkey *local_delayedkey)
{
	u8 *script = tal_arr(ctx, u8, 0);
	add_op(&script, OP_IF);
	add_push_key(&script, revocation_pubkey);
	add_op(&script, OP_ELSE);
	add_number(&script, to_self_delay);
	add_op(&script, OP_CHECKSEQUENCEVERIFY);
	add_op(&script, OP_DROP);
	add_push_key(&script, local_delayedkey);
	add_op(&script, OP_ENDIF);
	add_op(&script, OP_CHECKSIG);
	return script;
}

u8 **bitcoin_to_local_spend_revocation(const tal_t *ctx,
		const secp256k1_ecdsa_signature *revocation_sig,
		const u8 *wscript)
{
	/* BOLT #3:
	 *
	 * If a revoked commitment transaction is published, the other party
	 * can spend this output immediately with the following witness:
	 *
	 *    <revocation_sig> 1
	 */
	u8 **witness = tal_arr(ctx, u8 *, 3);

	witness[0] = stack_sig(witness, revocation_sig);
	witness[1] = stack_number(witness, 1);
	witness[2] = tal_dup_arr(witness, u8, wscript, tal_len(wscript), 0);

	return witness;
}

/* BOLT #3:
 *
 * #### Offered HTLC Outputs
 *
 * This output sends funds to an HTLC-timeout transaction after the HTLC
 * timeout, or to the remote peer using the payment preimage or the revocation
 * key.  The output is a P2WSH, with a witness script:
 *
 *     # To you with revocation key
 *     OP_DUP OP_HASH160 <RIPEMD160(SHA256(revocationkey))> OP_EQUAL
 *     OP_IF
 *         OP_CHECKSIG
 *     OP_ELSE
 *         <remote_htlckey> OP_SWAP OP_SIZE 32 OP_EQUAL
 *         OP_NOTIF
 *             # To me via HTLC-timeout transaction (timelocked).
 *             OP_DROP 2 OP_SWAP <local_htlckey> 2 OP_CHECKMULTISIG
 *         OP_ELSE
 *             # To you with preimage.
 *             OP_HASH160 <RIPEMD160(payment_hash)> OP_EQUALVERIFY
 *             OP_CHECKSIG
 *         OP_ENDIF
 *     OP_ENDIF
 */
u8 *bitcoin_wscript_htlc_offer_ripemd160(const tal_t *ctx,
					 const struct pubkey *localhtlckey,
					 const struct pubkey *remotehtlckey,
					 const struct ripemd160 *payment_ripemd,
					 const struct pubkey *revocationkey)
{
	u8 *script = tal_arr(ctx, u8, 0);
	struct ripemd160 ripemd;

	add_op(&script, OP_DUP);
	add_op(&script, OP_HASH160);
	pubkey_to_hash160(revocationkey, &ripemd);
	add_push_bytes(&script, &ripemd, sizeof(ripemd));
	add_op(&script, OP_EQUAL);
	add_op(&script, OP_IF);
	add_op(&script, OP_CHECKSIG);
	add_op(&script, OP_ELSE);
	add_push_key(&script, remotehtlckey);
	add_op(&script, OP_SWAP);
	add_op(&script, OP_SIZE);
	add_number(&script, 32);
	add_op(&script, OP_EQUAL);
	add_op(&script, OP_NOTIF);
	add_op(&script, OP_DROP);
	add_number(&script, 2);
	add_op(&script, OP_SWAP);
	add_push_key(&script, localhtlckey);
	add_number(&script, 2);
	add_op(&script, OP_CHECKMULTISIG);
	add_op(&script, OP_ELSE);
	add_op(&script, OP_HASH160);
	add_push_bytes(&script,
		       payment_ripemd->u.u8, sizeof(payment_ripemd->u.u8));
	add_op(&script, OP_EQUALVERIFY);
	add_op(&script, OP_CHECKSIG);
	add_op(&script, OP_ENDIF);
	add_op(&script, OP_ENDIF);

	return script;
}

u8 *bitcoin_wscript_htlc_offer(const tal_t *ctx,
			       const struct pubkey *localhtlckey,
			       const struct pubkey *remotehtlckey,
			       const struct sha256 *payment_hash,
			       const struct pubkey *revocationkey)
{
	struct ripemd160 ripemd;

	ripemd160(&ripemd, payment_hash->u.u8, sizeof(payment_hash->u));
	return bitcoin_wscript_htlc_offer_ripemd160(ctx, localhtlckey,
						    remotehtlckey,
						    &ripemd, revocationkey);
}

/* BOLT #3:
 *
 * #### Received HTLC Outputs
 *
 * This output sends funds to the remote peer after the HTLC timeout or using
 * the revocation key, or to an HTLC-success transaction with a successful
 * payment preimage. The output is a P2WSH, with a witness script:
 *
 *     # To you with revocation key
 *     OP_DUP OP_HASH160 <RIPEMD160(SHA256(revocationkey))> OP_EQUAL
 *     OP_IF
 *         OP_CHECKSIG
 *     OP_ELSE
 *         <remote_htlckey> OP_SWAP
 *             OP_SIZE 32 OP_EQUAL
 *         OP_IF
 *             # To me via HTLC-success transaction.
 *             OP_HASH160 <RIPEMD160(payment_hash)> OP_EQUALVERIFY
 *             2 OP_SWAP <local_htlckey> 2 OP_CHECKMULTISIG
 *         OP_ELSE
 *             # To you after timeout.
 *             OP_DROP <cltv_expiry> OP_CHECKLOCKTIMEVERIFY OP_DROP
 *             OP_CHECKSIG
 *         OP_ENDIF
 *     OP_ENDIF
 */
u8 *bitcoin_wscript_htlc_receive_ripemd(const tal_t *ctx,
					const struct abs_locktime *htlc_abstimeout,
					const struct pubkey *localhtlckey,
					const struct pubkey *remotehtlckey,
					const struct ripemd160 *payment_ripemd,
					const struct pubkey *revocationkey)
{
	u8 *script = tal_arr(ctx, u8, 0);
	struct ripemd160 ripemd;

	add_op(&script, OP_DUP);
	add_op(&script, OP_HASH160);
	pubkey_to_hash160(revocationkey, &ripemd);
	add_push_bytes(&script, &ripemd, sizeof(ripemd));
	add_op(&script, OP_EQUAL);
	add_op(&script, OP_IF);
	add_op(&script, OP_CHECKSIG);
	add_op(&script, OP_ELSE);
	add_push_key(&script, remotehtlckey);
	add_op(&script, OP_SWAP);
	add_op(&script, OP_SIZE);
	add_number(&script, 32);
	add_op(&script, OP_EQUAL);
	add_op(&script, OP_IF);
	add_op(&script, OP_HASH160);
	add_push_bytes(&script,
		       payment_ripemd->u.u8, sizeof(payment_ripemd->u.u8));
	add_op(&script, OP_EQUALVERIFY);
	add_number(&script, 2);
	add_op(&script, OP_SWAP);
	add_push_key(&script, localhtlckey);
	add_number(&script, 2);
	add_op(&script, OP_CHECKMULTISIG);
	add_op(&script, OP_ELSE);
	add_op(&script, OP_DROP);
	add_number(&script, htlc_abstimeout->locktime);
	add_op(&script, OP_CHECKLOCKTIMEVERIFY);
	add_op(&script, OP_DROP);
	add_op(&script, OP_CHECKSIG);
	add_op(&script, OP_ENDIF);
	add_op(&script, OP_ENDIF);

	return script;
}

u8 *bitcoin_wscript_htlc_receive(const tal_t *ctx,
				 const struct abs_locktime *htlc_abstimeout,
				 const struct pubkey *localhtlckey,
				 const struct pubkey *remotehtlckey,
				 const struct sha256 *payment_hash,
				 const struct pubkey *revocationkey)
{
	struct ripemd160 ripemd;

	ripemd160(&ripemd, payment_hash->u.u8, sizeof(payment_hash->u));
	return bitcoin_wscript_htlc_receive_ripemd(ctx, htlc_abstimeout,
						   localhtlckey, remotehtlckey,
						   &ripemd, revocationkey);
}

/* BOLT #3:
 *
 * ## HTLC-Timeout and HTLC-Success Transactions
 *
 *...
 *   * `txin[0]` witness stack: `0 <remotehtlcsig> <localhtlcsig>  <payment_preimage>` for HTLC-Success, `0 <remotehtlcsig> <localhtlcsig> 0` for HTLC-Timeout.
 */
u8 **bitcoin_witness_htlc_timeout_tx(const tal_t *ctx,
				     const secp256k1_ecdsa_signature *localhtlcsig,
				     const secp256k1_ecdsa_signature *remotehtlcsig,
				     const u8 *wscript)
{
	u8 **witness = tal_arr(ctx, u8 *, 5);

	witness[0] = stack_number(witness, 0);
	witness[1] = stack_sig(witness, remotehtlcsig);
	witness[2] = stack_sig(witness, localhtlcsig);
	witness[3] = stack_number(witness, 0);
	witness[4] = tal_dup_arr(witness, u8, wscript, tal_len(wscript), 0);

	return witness;
}

u8 **bitcoin_witness_htlc_success_tx(const tal_t *ctx,
				     const secp256k1_ecdsa_signature *localhtlcsig,
				     const secp256k1_ecdsa_signature *remotesig,
				     const struct preimage *preimage,
				     const u8 *wscript)
{
	u8 **witness = tal_arr(ctx, u8 *, 5);

	witness[0] = stack_number(witness, 0);
	witness[1] = stack_sig(witness, remotesig);
	witness[2] = stack_sig(witness, localhtlcsig);
	witness[3] = stack_preimage(witness, preimage);
	witness[4] = tal_dup_arr(witness, u8, wscript, tal_len(wscript), 0);

	return witness;
}
u8 *bitcoin_wscript_htlc_tx(const tal_t *ctx,
			    u16 to_self_delay,
			    const struct pubkey *revocation_pubkey,
			    const struct pubkey *local_delayedkey)
{
	u8 *script = tal_arr(ctx, u8, 0);

	/* BOLT #3:
	 *
	 * The witness script for the output is:
	 *
	 *     OP_IF
	 *         # Penalty transaction
	 *         <revocationkey>
	 *     OP_ELSE
	 *         `to_self_delay`
	 *         OP_CSV
	 *         OP_DROP
	 *         <local_delayedkey>
	 *     OP_ENDIF
	 *     OP_CHECKSIG
	 */
	add_op(&script, OP_IF);
	add_push_key(&script, revocation_pubkey);
	add_op(&script, OP_ELSE);
	add_number(&script, to_self_delay);
	add_op(&script, OP_CHECKSEQUENCEVERIFY);
	add_op(&script, OP_DROP);
	add_push_key(&script, local_delayedkey);
	add_op(&script, OP_ENDIF);
	add_op(&script, OP_CHECKSIG);

	return script;
}

bool scripteq(const tal_t *s1, const tal_t *s2)
{
	memcheck(s1, tal_len(s1));
	memcheck(s2, tal_len(s2));

	if (tal_len(s1) != tal_len(s2))
		return false;
	return memcmp(s1, s2, tal_len(s1)) == 0;
}