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-rw-r--r--src/ecdsa_impl.h94
1 files changed, 48 insertions, 46 deletions
diff --git a/src/ecdsa_impl.h b/src/ecdsa_impl.h
index c3400042d8..5f54b59faa 100644
--- a/src/ecdsa_impl.h
+++ b/src/ecdsa_impl.h
@@ -46,68 +46,73 @@ static const secp256k1_fe secp256k1_ecdsa_const_p_minus_order = SECP256K1_FE_CON
0, 0, 0, 1, 0x45512319UL, 0x50B75FC4UL, 0x402DA172UL, 0x2FC9BAEEUL
);
-static int secp256k1_der_read_len(const unsigned char **sigp, const unsigned char *sigend) {
- int lenleft, b1;
- size_t ret = 0;
+static int secp256k1_der_read_len(size_t *len, const unsigned char **sigp, const unsigned char *sigend) {
+ size_t lenleft;
+ unsigned char b1;
+ VERIFY_CHECK(len != NULL);
+ *len = 0;
if (*sigp >= sigend) {
- return -1;
+ return 0;
}
b1 = *((*sigp)++);
if (b1 == 0xFF) {
/* X.690-0207 8.1.3.5.c the value 0xFF shall not be used. */
- return -1;
+ return 0;
}
if ((b1 & 0x80) == 0) {
/* X.690-0207 8.1.3.4 short form length octets */
- return b1;
+ *len = b1;
+ return 1;
}
if (b1 == 0x80) {
/* Indefinite length is not allowed in DER. */
- return -1;
+ return 0;
}
/* X.690-207 8.1.3.5 long form length octets */
- lenleft = b1 & 0x7F;
- if (lenleft > sigend - *sigp) {
- return -1;
+ lenleft = b1 & 0x7F; /* lenleft is at least 1 */
+ if (lenleft > (size_t)(sigend - *sigp)) {
+ return 0;
}
if (**sigp == 0) {
/* Not the shortest possible length encoding. */
- return -1;
+ return 0;
}
- if ((size_t)lenleft > sizeof(size_t)) {
+ if (lenleft > sizeof(size_t)) {
/* The resulting length would exceed the range of a size_t, so
* certainly longer than the passed array size.
*/
- return -1;
+ return 0;
}
while (lenleft > 0) {
- ret = (ret << 8) | **sigp;
- if (ret + lenleft > (size_t)(sigend - *sigp)) {
- /* Result exceeds the length of the passed array. */
- return -1;
- }
+ *len = (*len << 8) | **sigp;
(*sigp)++;
lenleft--;
}
- if (ret < 128) {
+ if (*len > (size_t)(sigend - *sigp)) {
+ /* Result exceeds the length of the passed array. */
+ return 0;
+ }
+ if (*len < 128) {
/* Not the shortest possible length encoding. */
- return -1;
+ return 0;
}
- return ret;
+ return 1;
}
static int secp256k1_der_parse_integer(secp256k1_scalar *r, const unsigned char **sig, const unsigned char *sigend) {
int overflow = 0;
unsigned char ra[32] = {0};
- int rlen;
+ size_t rlen;
if (*sig == sigend || **sig != 0x02) {
/* Not a primitive integer (X.690-0207 8.3.1). */
return 0;
}
(*sig)++;
- rlen = secp256k1_der_read_len(sig, sigend);
- if (rlen <= 0 || (*sig) + rlen > sigend) {
+ if (secp256k1_der_read_len(&rlen, sig, sigend) == 0) {
+ return 0;
+ }
+ if (rlen == 0 || *sig + rlen > sigend) {
/* Exceeds bounds or not at least length 1 (X.690-0207 8.3.1). */
return 0;
}
@@ -123,8 +128,11 @@ static int secp256k1_der_parse_integer(secp256k1_scalar *r, const unsigned char
/* Negative. */
overflow = 1;
}
- while (rlen > 0 && **sig == 0) {
- /* Skip leading zero bytes */
+ /* There is at most one leading zero byte:
+ * if there were two leading zero bytes, we would have failed and returned 0
+ * because of excessive 0x00 padding already. */
+ if (rlen > 0 && **sig == 0) {
+ /* Skip leading zero byte */
rlen--;
(*sig)++;
}
@@ -144,18 +152,16 @@ static int secp256k1_der_parse_integer(secp256k1_scalar *r, const unsigned char
static int secp256k1_ecdsa_sig_parse(secp256k1_scalar *rr, secp256k1_scalar *rs, const unsigned char *sig, size_t size) {
const unsigned char *sigend = sig + size;
- int rlen;
+ size_t rlen;
if (sig == sigend || *(sig++) != 0x30) {
/* The encoding doesn't start with a constructed sequence (X.690-0207 8.9.1). */
return 0;
}
- rlen = secp256k1_der_read_len(&sig, sigend);
- if (rlen < 0 || sig + rlen > sigend) {
- /* Tuple exceeds bounds */
+ if (secp256k1_der_read_len(&rlen, &sig, sigend) == 0) {
return 0;
}
- if (sig + rlen != sigend) {
- /* Garbage after tuple. */
+ if (rlen != (size_t)(sigend - sig)) {
+ /* Tuple exceeds bounds or garage after tuple. */
return 0;
}
@@ -274,6 +280,7 @@ static int secp256k1_ecdsa_sig_sign(const secp256k1_ecmult_gen_context *ctx, sec
secp256k1_ge r;
secp256k1_scalar n;
int overflow = 0;
+ int high;
secp256k1_ecmult_gen(ctx, &rp, nonce);
secp256k1_ge_set_gej(&r, &rp);
@@ -281,15 +288,11 @@ static int secp256k1_ecdsa_sig_sign(const secp256k1_ecmult_gen_context *ctx, sec
secp256k1_fe_normalize(&r.y);
secp256k1_fe_get_b32(b, &r.x);
secp256k1_scalar_set_b32(sigr, b, &overflow);
- /* These two conditions should be checked before calling */
- VERIFY_CHECK(!secp256k1_scalar_is_zero(sigr));
- VERIFY_CHECK(overflow == 0);
-
if (recid) {
/* The overflow condition is cryptographically unreachable as hitting it requires finding the discrete log
* of some P where P.x >= order, and only 1 in about 2^127 points meet this criteria.
*/
- *recid = (overflow ? 2 : 0) | (secp256k1_fe_is_odd(&r.y) ? 1 : 0);
+ *recid = (overflow << 1) | secp256k1_fe_is_odd(&r.y);
}
secp256k1_scalar_mul(&n, sigr, seckey);
secp256k1_scalar_add(&n, &n, message);
@@ -298,16 +301,15 @@ static int secp256k1_ecdsa_sig_sign(const secp256k1_ecmult_gen_context *ctx, sec
secp256k1_scalar_clear(&n);
secp256k1_gej_clear(&rp);
secp256k1_ge_clear(&r);
- if (secp256k1_scalar_is_zero(sigs)) {
- return 0;
- }
- if (secp256k1_scalar_is_high(sigs)) {
- secp256k1_scalar_negate(sigs, sigs);
- if (recid) {
- *recid ^= 1;
- }
+ high = secp256k1_scalar_is_high(sigs);
+ secp256k1_scalar_cond_negate(sigs, high);
+ if (recid) {
+ *recid ^= high;
}
- return 1;
+ /* P.x = order is on the curve, so technically sig->r could end up being zero, which would be an invalid signature.
+ * This is cryptographically unreachable as hitting it requires finding the discrete log of P.x = N.
+ */
+ return !secp256k1_scalar_is_zero(sigr) & !secp256k1_scalar_is_zero(sigs);
}
#endif /* SECP256K1_ECDSA_IMPL_H */
generated by cgit v1.2.3 (git 2.26.2) at 2024-09-04 18:52:32 +0000