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signature.c
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signature.c
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#include <ccan/cast/cast.h>
#include "privkey.h"
#include "pubkey.h"
#include "script.h"
#include "secp256k1.h"
#include "shadouble.h"
#include "signature.h"
#include "tx.h"
#include <assert.h>
#undef DEBUG
#ifdef DEBUG
#include <ccan/err/err.h>
#include <stdio.h>
#define SHA_FMT \
"%02x%02x%02x%02x%02x%02x%02x%02x" \
"%02x%02x%02x%02x%02x%02x%02x%02x" \
"%02x%02x%02x%02x%02x%02x%02x%02x" \
"%02x%02x%02x%02x%02x%02x%02x%02x"
#define SHA_VALS(e) \
e[0], e[1], e[2], e[3], e[4], e[5], e[6], e[7], \
e[8], e[9], e[10], e[11], e[12], e[13], e[14], e[15], \
e[16], e[17], e[18], e[19], e[20], e[21], e[22], e[23], \
e[24], e[25], e[25], e[26], e[28], e[29], e[30], e[31]
static void dump_tx(const char *msg,
const struct bitcoin_tx *tx, size_t inputnum,
const u8 *script, size_t script_len,
const struct pubkey *key,
const struct sha256_double *h)
{
size_t i, j;
warnx("%s tx version %u locktime %#x:",
msg, tx->version, tx->lock_time);
for (i = 0; i < tx->input_count; i++) {
warnx("input[%zu].txid = "SHA_FMT, i,
SHA_VALS(tx->input[i].txid.sha.u.u8));
warnx("input[%zu].index = %u", i, tx->input[i].index);
}
for (i = 0; i < tx->output_count; i++) {
warnx("output[%zu].amount = %llu",
i, (long long)tx->output[i].amount);
warnx("output[%zu].script = %llu",
i, (long long)tx->output[i].script_length);
for (j = 0; j < tx->output[i].script_length; j++)
fprintf(stderr, "%02x", tx->output[i].script[j]);
fprintf(stderr, "\n");
}
warnx("input[%zu].script = %zu", inputnum, script_len);
for (i = 0; i < script_len; i++)
fprintf(stderr, "%02x", script[i]);
if (key) {
fprintf(stderr, "\nPubkey: ");
for (i = 0; i < pubkey_len(key); i++)
fprintf(stderr, "%02x", key->key[i]);
fprintf(stderr, "\n");
}
if (h) {
fprintf(stderr, "\nHash: ");
for (i = 0; i < sizeof(h->sha.u.u8); i++)
fprintf(stderr, "%02x", h->sha.u.u8[i]);
fprintf(stderr, "\n");
}
}
#else
static void dump_tx(const char *msg,
const struct bitcoin_tx *tx, size_t inputnum,
const u8 *script, size_t script_len,
const struct pubkey *key,
const struct sha256_double *h)
{
}
#endif
bool sign_hash(const tal_t *ctx, const struct privkey *privkey,
const struct sha256_double *h,
struct signature *s)
{
secp256k1_context_t *secpctx;
bool ok;
secpctx = secp256k1_context_create(SECP256K1_CONTEXT_SIGN);
if (!secpctx)
return false;
#ifdef USE_SCHNORR
ok = secp256k1_schnorr_sign(secpctx, h->sha.u.u8,
(unsigned char *)s,
privkey->secret, NULL, NULL);
#else
ok = secp256k1_ecdsa_sign_compact(secpctx, h->sha.u.u8,
(unsigned char *)s,
privkey->secret, NULL, NULL, NULL);
#endif
secp256k1_context_destroy(secpctx);
return ok;
}
/* Only does SIGHASH_ALL */
static void sha256_tx_one_input(struct bitcoin_tx *tx,
size_t input_num,
const u8 *script, size_t script_len,
struct sha256_double *hash)
{
struct sha256_ctx ctx = SHA256_INIT;
size_t i;
assert(input_num < tx->input_count);
/* You must have all inputs zeroed to start. */
for (i = 0; i < tx->input_count; i++)
assert(tx->input[i].script_length == 0);
tx->input[input_num].script_length = script_len;
tx->input[input_num].script = cast_const(u8 *, script);
sha256_init(&ctx);
sha256_tx_for_sig(&ctx, tx, input_num);
sha256_le32(&ctx, SIGHASH_ALL);
sha256_double_done(&ctx, hash);
/* Reset it for next time. */
tx->input[input_num].script_length = 0;
tx->input[input_num].script = NULL;
}
/* Only does SIGHASH_ALL */
bool sign_tx_input(const tal_t *ctx, struct bitcoin_tx *tx,
unsigned int in,
const u8 *subscript, size_t subscript_len,
const struct privkey *privkey, const struct pubkey *key,
struct signature *sig)
{
struct sha256_double hash;
sha256_tx_one_input(tx, in, subscript, subscript_len, &hash);
dump_tx("Signing", tx, in, subscript, subscript_len, key, &hash);
return sign_hash(ctx, privkey, &hash, sig);
}
static bool check_signed_hash(const struct sha256_double *hash,
const struct signature *signature,
const struct pubkey *key)
{
int ret;
secp256k1_context_t *secpctx;
secpctx = secp256k1_context_create(SECP256K1_CONTEXT_VERIFY);
if (!secpctx)
return false;
#ifdef USE_SCHNORR
ret = secp256k1_schnorr_verify(secpctx, hash->sha.u.u8,
(unsigned char *)signature,
key->key, pubkey_len(key));
#else
{
u8 der[72];
size_t der_len;
/* FIXME: secp256k1 missing secp256k1_ecdsa_verify_compact */
der_len = signature_to_der(der, signature);
ret = secp256k1_ecdsa_verify(secpctx, hash->sha.u.u8,
der, der_len,
key->key, pubkey_len(key));
}
#endif
secp256k1_context_destroy(secpctx);
return ret == 1;
}
bool check_tx_sig(struct bitcoin_tx *tx, size_t input_num,
const u8 *redeemscript, size_t redeemscript_len,
const struct pubkey *key,
const struct bitcoin_signature *sig)
{
struct sha256_double hash;
bool ret;
assert(input_num < tx->input_count);
sha256_tx_one_input(tx, input_num, redeemscript, redeemscript_len,
&hash);
/* We only use SIGHASH_ALL for the moment. */
if (sig->stype != SIGHASH_ALL)
return false;
ret = check_signed_hash(&hash, &sig->sig, key);
if (!ret)
dump_tx("Sig failed", tx, input_num,
redeemscript, redeemscript_len, key, &hash);
return ret;
}
bool check_2of2_sig(struct bitcoin_tx *tx, size_t input_num,
const u8 *redeemscript, size_t redeemscript_len,
const struct pubkey *key1, const struct pubkey *key2,
const struct bitcoin_signature *sig1,
const struct bitcoin_signature *sig2)
{
struct sha256_double hash;
assert(input_num < tx->input_count);
sha256_tx_one_input(tx, input_num, redeemscript, redeemscript_len,
&hash);
/* We only use SIGHASH_ALL for the moment. */
if (sig1->stype != SIGHASH_ALL || sig2->stype != SIGHASH_ALL)
return false;
return check_signed_hash(&hash, &sig1->sig, key1)
&& check_signed_hash(&hash, &sig2->sig, key2);
}
/* Stolen direct from bitcoin/src/script/sign.cpp:
// Copyright (c) 2009-2010 Satoshi Nakamoto
// Copyright (c) 2009-2014 The Bitcoin Core developers
// Distributed under the MIT software license, see the accompanying
// file COPYING or http://www.opensource.org/licenses/mit-license.php.
*/
static bool IsValidSignatureEncoding(const unsigned char sig[], size_t len)
{
// Format: 0x30 [total-length] 0x02 [R-length] [R] 0x02 [S-length] [S] [sighash]
// * total-length: 1-byte length descriptor of everything that follows,
// excluding the sighash byte.
// * R-length: 1-byte length descriptor of the R value that follows.
// * R: arbitrary-length big-endian encoded R value. It must use the shortest
// possible encoding for a positive integers (which means no null bytes at
// the start, except a single one when the next byte has its highest bit set).
// * S-length: 1-byte length descriptor of the S value that follows.
// * S: arbitrary-length big-endian encoded S value. The same rules apply.
// * sighash: 1-byte value indicating what data is hashed (not part of the DER
// signature)
// Minimum and maximum size constraints.
if (len < 9) return false;
if (len > 73) return false;
// A signature is of type 0x30 (compound).
if (sig[0] != 0x30) return false;
// Make sure the length covers the entire signature.
if (sig[1] != len - 3) return false;
// Extract the length of the R element.
unsigned int lenR = sig[3];
// Make sure the length of the S element is still inside the signature.
if (5 + lenR >= len) return false;
// Extract the length of the S element.
unsigned int lenS = sig[5 + lenR];
// Verify that the length of the signature matches the sum of the length
// of the elements.
if ((size_t)(lenR + lenS + 7) != len) return false;
// Check whether the R element is an integer.
if (sig[2] != 0x02) return false;
// Zero-length integers are not allowed for R.
if (lenR == 0) return false;
// Negative numbers are not allowed for R.
if (sig[4] & 0x80) return false;
// Null bytes at the start of R are not allowed, unless R would
// otherwise be interpreted as a negative number.
if (lenR > 1 && (sig[4] == 0x00) && !(sig[5] & 0x80)) return false;
// Check whether the S element is an integer.
if (sig[lenR + 4] != 0x02) return false;
// Zero-length integers are not allowed for S.
if (lenS == 0) return false;
// Negative numbers are not allowed for S.
if (sig[lenR + 6] & 0x80) return false;
// Null bytes at the start of S are not allowed, unless S would otherwise be
// interpreted as a negative number.
if (lenS > 1 && (sig[lenR + 6] == 0x00) && !(sig[lenR + 7] & 0x80)) return false;
return true;
}
/* DER encode a value, return length used. */
static size_t der_encode_val(const u8 *val, u8 *der)
{
size_t len = 0, val_len = 32;
der[len++] = 0x2; /* value type. */
/* Strip leading zeroes. */
while (val_len && val[0] == 0) {
val++;
val_len--;
}
/* Add zero byte if it would otherwise be signed. */
if (val[0] & 0x80) {
der[len++] = 1 + val_len; /* value length */
der[len++] = 0;
} else
der[len++] = val_len; /* value length */
memcpy(der + len, val, val_len);
return len + val_len;
}
size_t signature_to_der(u8 der[72], const struct signature *sig)
{
size_t len = 0;
der[len++] = 0x30; /* Type */
der[len++] = 0; /* Total length after this: fill it at end. */
len += der_encode_val(sig->r, der + len);
len += der_encode_val(sig->s, der + len);
/* Fix up total length */
der[1] = len - 2;
/* IsValidSignatureEncoding() expect extra byte for sighash */
assert(IsValidSignatureEncoding(der, len + 1));
return len;
}
/* Signature must have low S value. */
bool sig_valid(const struct signature *sig)
{
#ifdef USE_SCHNORR
/* FIXME: Is there some sanity check we can do here? */
return true;
#else
return (sig->s[0] & 0x80) == 0;
#endif
}