create-commit-tx: create a commit tx.

Required for unilateral close.  Also lets us test stealing funds
from a revoked transaction.

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

Makefile

@@ -3,7 +3,7 @@
 # Needs to have oneof support: Ubuntu vivid's is too old :(
 PROTOCC:=protoc-c
 
-PROGRAMS := open-channel open-anchor-scriptsigs leak-anchor-sigs open-commit-sig check-commit-sig check-anchor-scriptsigs get-anchor-depth create-steal-tx create-commit-spend-tx close-channel create-close-tx update-channel update-channel-accept update-channel-signature update-channel-complete
+PROGRAMS := open-channel open-anchor-scriptsigs leak-anchor-sigs open-commit-sig check-commit-sig check-anchor-scriptsigs get-anchor-depth create-steal-tx create-commit-spend-tx close-channel create-close-tx update-channel update-channel-accept update-channel-signature update-channel-complete create-commit-tx
 
 HELPER_OBJS := base58.o lightning.pb-c.o shadouble.o pkt.o bitcoin_script.o permute_tx.o signature.o bitcoin_tx.o bitcoin_address.o anchor.o commit_tx.o pubkey.o opt_bits.o close_tx.o find_p2sh_out.o
 

create-commit-tx.c

@@ -0,0 +1,125 @@
+/* My example:
+ * ./open-commit-sig A-open.pb B-open.pb cUBCjrdJu8tfvM7FT8So6aqs6G6bZS1Cax6Rc9rFzYL6nYG4XNEC A-leak-anchor-sigs.pb B-leak-anchor-sigs.pb > A-commit-sig.pb
+ * ./open-commit-sig B-open.pb A-open.pb cQXhbUnNRsFcdzTQwjbCrud5yVskHTEas7tZPUWoJYNk5htGQrpi B-leak-anchor-sigs.pb A-leak-anchor-sigs.pb > B-commit-sig.pb
+ */
+#include <ccan/crypto/shachain/shachain.h>
+#include <ccan/short_types/short_types.h>
+#include <ccan/tal/tal.h>
+#include <ccan/opt/opt.h>
+#include <ccan/str/hex/hex.h>
+#include <ccan/err/err.h>
+#include <ccan/read_write_all/read_write_all.h>
+#include "lightning.pb-c.h"
+#include "anchor.h"
+#include "base58.h"
+#include "pkt.h"
+#include "bitcoin_script.h"
+#include "permute_tx.h"
+#include "signature.h"
+#include "commit_tx.h"
+#include "pubkey.h"
+#include "find_p2sh_out.h"
+#include <openssl/ec.h>
+#include <unistd.h>
+
+int main(int argc, char *argv[])
+{
+	const tal_t *ctx = tal_arr(NULL, char, 0);
+	OpenChannel *o1, *o2;
+	Update *update;
+	UpdateAccept *update_acc;
+	struct bitcoin_tx *anchor, *commit;
+	struct sha256_double anchor_txid;
+	EC_KEY *privkey;
+	bool testnet;
+	struct bitcoin_signature sig1, sig2;
+	size_t i;
+	struct pubkey pubkey1, pubkey2;
+	u8 *redeemscript, *tx_arr;
+	char *tx_hex;
+	int64_t delta;
+	struct sha256 rhash;
+
+	err_set_progname(argv[0]);
+
+	opt_register_noarg("--help|-h", opt_usage_and_exit,
+			   "<anchor-tx> <open-channel-file1> <open-channel-file2> <final-update> <final-update-accept> <commit-privkey> [<previous-updates>]\n"
+			   "Create the signature needed for the commit transaction",
+			   "Print this message.");
+
+ 	opt_parse(&argc, argv, opt_log_stderr_exit);
+
+	if (argc < 7)
+		opt_usage_exit_fail("Expected 6+ arguments");
+
+	anchor = bitcoin_tx_from_file(ctx, argv[1]);
+	bitcoin_txid(anchor, &anchor_txid);
+	o1 = pkt_from_file(argv[2], PKT__PKT_OPEN)->open;
+	o2 = pkt_from_file(argv[3], PKT__PKT_OPEN)->open;
+
+	update = pkt_from_file(argv[4], PKT__PKT_UPDATE)->update;
+	update_acc = pkt_from_file(argv[5], PKT__PKT_UPDATE_ACCEPT)->update_accept;
+
+	privkey = key_from_base58(argv[6], strlen(argv[6]), &testnet, &pubkey1);
+	if (!privkey)
+		errx(1, "Invalid private key '%s'", argv[6]);
+	if (!testnet)
+		errx(1, "Private key '%s' not on testnet!", argv[6]);
+
+	/* Get pubkeys */
+	if (!proto_to_pubkey(o1->anchor->pubkey, &pubkey2))
+		errx(1, "Invalid o1 anchor pubkey");
+	if (pubkey_len(&pubkey1) != pubkey_len(&pubkey2)
+	    || memcmp(pubkey1.key, pubkey2.key, pubkey_len(&pubkey2)) != 0)
+		errx(1, "o1 pubkey != this privkey");
+	if (!proto_to_pubkey(o2->anchor->pubkey, &pubkey2))
+		errx(1, "Invalid o2 anchor pubkey");
+
+	/* Figure out cumulative delta since anchor. */
+	delta = update->delta;
+	for (i = 7; i < argc; i++) {
+		Update *u = pkt_from_file(argv[i], PKT__PKT_UPDATE)->update;
+		delta += u->delta;
+	}
+
+	redeemscript = bitcoin_redeem_2of2(ctx, &pubkey1, &pubkey2);
+
+	/* Now create commitment tx to spend 2/2 output of anchor. */
+	proto_to_sha256(update->revocation_hash, &rhash);
+	commit = create_commit_tx(ctx, o1, o2, &rhash, delta, &anchor_txid,
+				  find_p2sh_out(anchor, redeemscript));
+
+	/* If contributions don't exceed fees, this fails. */
+	if (!commit)
+		errx(1, "Bad commit amounts");
+
+	/* We generate our signature. */
+	sig1.stype = SIGHASH_ALL;
+	sign_tx_input(ctx, commit, 0, redeemscript, tal_count(redeemscript),
+		      privkey, &pubkey1, &sig1.sig);
+
+	/* Their signatures comes from the update_accept packet. */
+	sig2.stype = SIGHASH_ALL;
+	if (!proto_to_signature(update_acc->sig, &sig2.sig))
+		errx(1, "Invalid update-accept sig");
+
+	if (!check_2of2_sig(commit, 0, redeemscript, tal_count(redeemscript),
+			    &pubkey1, &pubkey2, &sig1, &sig2))
+		errx(1, "Signature failed");
+
+	/* Create p2sh input for commit */
+	commit->input[0].script = scriptsig_p2sh_2of2(commit, &sig1, &sig2,
+						      &pubkey1, &pubkey2);
+	commit->input[0].script_length = tal_count(commit->input[0].script);
+
+	/* Print it out in hex. */
+	tx_arr = linearize_tx(ctx, commit);
+	tx_hex = tal_arr(tx_arr, char, hex_str_size(tal_count(tx_arr)));
+	hex_encode(tx_arr, tal_count(tx_arr), tx_hex, tal_count(tx_hex));
+
+	if (!write_all(STDOUT_FILENO, tx_hex, strlen(tx_hex)))
+		err(1, "Writing out transaction");
+
+	tal_free(ctx);
+	return 0;
+}