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ecdsa: VERIFY_CHECK result of _fe_set_b32_limit #1839

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Merged
real-or-random merged 1 commit into from
Mar 25, 2026
+10 −2
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ecdsa: VERIFY_CHECK result of _fe_set_b32_limit #1839

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12 changes: 10 additions & 2 deletions src/ecdsa_impl.h
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Original file line number Diff line number Diff line change
Expand Up @@ -196,6 +196,7 @@ static int secp256k1_ecdsa_sig_verify(const secp256k1_scalar *sigr, const secp25
unsigned char c[32];
secp256k1_scalar sn, u1, u2;
#if !defined(EXHAUSTIVE_TEST_ORDER)
int range;
secp256k1_fe xr;
#endif
secp256k1_gej pubkeyj;
Expand Down Expand Up @@ -226,9 +227,16 @@ static int secp256k1_ecdsa_sig_verify(const secp256k1_scalar *sigr, const secp25
return secp256k1_scalar_eq(sigr, &computed_r);
}
#else

/* Interpret sigr as a field element xr */
secp256k1_scalar_get_b32(c, sigr);
/* we can ignore the fe_set_b32_limit return value, because we know the input is in range */
(void)secp256k1_fe_set_b32_limit(&xr, c);
range = secp256k1_fe_set_b32_limit(&xr, c);
#ifdef VERIFY
/* We know that c is in range; it comes from a scalar. */
VERIFY_CHECK(range);
#else
(void)range;
#endif

/** We now have the recomputed R point in pr, and its claimed x coordinate (modulo n)
* in xr. Naively, we would extract the x coordinate from pr (requiring a inversion modulo p),
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