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fix for issue #116

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This commit is contained in:
Karel Miko 2026-04-23 23:01:20 +02:00 • committed by Steffen Jaeckel
parent 8e9b1983af
commit 66a2e73eb8
4 changed files with 49 additions and 0 deletions
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5
src/math/fp/ltc_ecc_fp_mulmod.c
View file

@ -1224,6 +1224,11 @@ int ltc_ecc_fp_mulmod(void *k, ecc_point *G, ecc_point *R, void *a, void *modulu
int idx, err;
void *mp, *mu;
if (ltc_mp_iszero(k) == LTC_MP_YES) {
/* 0 * G is the point at infinity */
return ltc_ecc_set_point_xyz(1, 1, 0, R);
}
mp = NULL;
mu = NULL;
LTC_MUTEX_LOCK(&ltc_ecc_fp_lock);

4
src/pk/ecc/ltc_ecc_mulmod.c
View file

@ -42,6 +42,10 @@ int ltc_ecc_mulmod(const void *k, const ecc_point *G, ecc_point *R, const void *
/* return the point at infinity */
return ltc_ecc_set_point_xyz(1, 1, 0, R);
}
if (ltc_mp_iszero(k) == LTC_MP_YES) {
/* 0 * G is the point at infinity */
return ltc_ecc_set_point_xyz(1, 1, 0, R);
}
/* init montgomery reduction */
if ((err = ltc_mp_montgomery_setup(modulus, &mp)) != CRYPT_OK) { goto error; }

4
src/pk/ecc/ltc_ecc_mulmod_timing.c
View file

@ -40,6 +40,10 @@ int ltc_ecc_mulmod(const void *k, const ecc_point *G, ecc_point *R, const void *
/* return the point at infinity */
return ltc_ecc_set_point_xyz(1, 1, 0, R);
}
if (ltc_mp_iszero(k) == LTC_MP_YES) {
/* 0 * G is the point at infinity */
return ltc_ecc_set_point_xyz(1, 1, 0, R);
}
/* init montgomery reduction */
if ((err = ltc_mp_montgomery_setup(modulus, &mp)) != CRYPT_OK) { goto error; }

36
tests/ecc_test.c
View file

@ -245,6 +245,41 @@ static int s_ecc_issue630(void)
return 0;
}
/* https://github.com/libtom/libtomcrypt/issues/116
verifies that ECDSA verification succeeds for an all-zero hash when the non-Shamir fallback is used
i.e. when u1 == 0 and the code path computes 0 * G + u2 * Q via two separate point multiplications
*/
static int s_ecc_issue116(void)
{
const ltc_ecc_curve *dp;
ecc_key key;
int err, stat;
unsigned long siglen;
unsigned char hash[20];
unsigned char sig[128];
ltc_ecc_sig_opts sig_opts = { .type = LTC_ECCSIG_RFC7518, .prng = &yarrow_prng, .wprng = find_prng("yarrow") };
int (*saved_mul2add)(const ecc_point *A, void *kA, const ecc_point *B, void *kB, ecc_point *C, const void *ma, const void *modulus);
XMEMSET(hash, 0, sizeof(hash));
DO(ecc_find_curve("SECP256R1", &dp));
DO(ecc_make_key_ex(&yarrow_prng, find_prng("yarrow"), &key, dp));
siglen = sizeof(sig);
DO(ecc_sign_hash_v2(hash, sizeof(hash), sig, &siglen, &sig_opts, &key));
saved_mul2add = ltc_mp.ecc_mul2add;
ltc_mp.ecc_mul2add = NULL;
stat = 0;
err = ecc_verify_hash_v2(sig, siglen, hash, sizeof(hash), &(ltc_ecc_sig_opts){ .type = LTC_ECCSIG_RFC7518 }, &stat, &key);
ltc_mp.ecc_mul2add = saved_mul2add;
ecc_free(&key);
if (err != CRYPT_OK) return err;
if (stat != 1) return CRYPT_FAIL_TESTVECTOR;
return CRYPT_OK;
}
/* https://github.com/libtom/libtomcrypt/issues/108 */
static int s_ecc_issue108(void)
{
@ -2246,6 +2281,7 @@ int ecc_test(void)
DO(s_ecc_issue108());
DO(s_ecc_issue443_447());
DO(s_ecc_issue630());
DO(s_ecc_issue116());
#ifdef LTC_ECC_SHAMIR
DO(s_ecc_test_shamir());
DO(s_ecc_test_recovery());