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mp_sqrt: TonelliShanks algorithm doesn't handle zero

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(0 * 0) mod p = 0.
Modular reduce n and shortcut when 0.
This commit is contained in:
Sean Parkinson
2021-11-16 09:23:07 +10:00
parent b2ba6f94af
commit d3fc8c229a
1 changed files with 25 additions and 6 deletions
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31
wolfcrypt/src/ecc.c
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@ -12382,15 +12382,16 @@ int mp_sqrtmod_prime(mp_int* n, mp_int* prime, mp_int* ret)
mp_int *M = (mp_int *)XMALLOC(sizeof(mp_int), NULL, DYNAMIC_TYPE_ECC_BUFFER);
mp_int *T = (mp_int *)XMALLOC(sizeof(mp_int), NULL, DYNAMIC_TYPE_ECC_BUFFER);
mp_int *R = (mp_int *)XMALLOC(sizeof(mp_int), NULL, DYNAMIC_TYPE_ECC_BUFFER);
mp_int *N = (mp_int *)XMALLOC(sizeof(mp_int), NULL, DYNAMIC_TYPE_ECC_BUFFER);
mp_int *two = (mp_int *)XMALLOC(sizeof(mp_int), NULL, DYNAMIC_TYPE_ECC_BUFFER);
#else
mp_int t1[1], C[1], Q[1], S[1], Z[1], M[1], T[1], R[1], two[1];
mp_int t1[1], C[1], Q[1], S[1], Z[1], M[1], T[1], R[1], N[1], two[1];
#endif
SAVE_VECTOR_REGISTERS(res = _svr_ret; goto out;);
if ((mp_init_multi(t1, C, Q, S, Z, M) != MP_OKAY) ||
(mp_init_multi(T, R, two, NULL, NULL, NULL) != MP_OKAY)) {
(mp_init_multi(T, R, N, two, NULL, NULL) != MP_OKAY)) {
res = MP_INIT_E;
goto out;
}
@ -12404,6 +12405,7 @@ int mp_sqrtmod_prime(mp_int* n, mp_int* prime, mp_int* ret)
(M == NULL) ||
(T == NULL) ||
(R == NULL) ||
(N == NULL) ||
(two == NULL)) {
res = MP_MEM;
goto out;
@ -12427,8 +12429,19 @@ int mp_sqrtmod_prime(mp_int* n, mp_int* prime, mp_int* ret)
goto out;
}
/* reduce n to less than prime */
res = mp_mod(n, prime, N);
if (res != MP_OKAY) {
goto out;
}
/* when N is zero, sqrt is zero */
if (mp_iszero(N)) {
mp_set(ret, 0);
goto out;
}
/* is quadratic non-residue mod prime */
if ((res = mp_jacobi(n, prime, &legendre)) != MP_OKAY) {
if ((res = mp_jacobi(N, prime, &legendre)) != MP_OKAY) {
goto out;
}
if (legendre == -1) {
@ -12449,7 +12462,7 @@ int mp_sqrtmod_prime(mp_int* n, mp_int* prime, mp_int* ret)
if (res == MP_OKAY)
res = mp_div_2(t1, t1);
if (res == MP_OKAY)
res = mp_exptmod(n, t1, prime, ret);
res = mp_exptmod(N, t1, prime, ret);
done = 1;
}
@ -12504,11 +12517,11 @@ int mp_sqrtmod_prime(mp_int* n, mp_int* prime, mp_int* ret)
/* R = n ^ ((Q + 1) / 2) mod prime */
if (res == MP_OKAY)
res = mp_exptmod(n, t1, prime, R);
res = mp_exptmod(N, t1, prime, R);
/* T = n ^ Q mod prime */
if (res == MP_OKAY)
res = mp_exptmod(n, Q, prime, T);
res = mp_exptmod(N, Q, prime, T);
/* M = S */
if (res == MP_OKAY)
@ -12611,6 +12624,11 @@ int mp_sqrtmod_prime(mp_int* n, mp_int* prime, mp_int* ret)
mp_clear(R);
XFREE(R, NULL, DYNAMIC_TYPE_ECC_BUFFER);
}
if (N) {
if (res != MP_INIT_E)
mp_clear(N);
XFREE(N, NULL, DYNAMIC_TYPE_ECC_BUFFER);
}
if (two) {
if (res != MP_INIT_E)
mp_clear(two);
@ -12626,6 +12644,7 @@ int mp_sqrtmod_prime(mp_int* n, mp_int* prime, mp_int* ret)
mp_clear(M);
mp_clear(T);
mp_clear(R);
mp_clear(N);
mp_clear(two);
}
#endif