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path: root/libtommath/bn_mp_sqrtmod_prime.c
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-rw-r--r--libtommath/bn_mp_sqrtmod_prime.c198
1 files changed, 96 insertions, 102 deletions
diff --git a/libtommath/bn_mp_sqrtmod_prime.c b/libtommath/bn_mp_sqrtmod_prime.c
index 968729e..a833ed7 100644
--- a/libtommath/bn_mp_sqrtmod_prime.c
+++ b/libtommath/bn_mp_sqrtmod_prime.c
@@ -1,13 +1,7 @@
-#include <tommath_private.h>
+#include "tommath_private.h"
#ifdef BN_MP_SQRTMOD_PRIME_C
-/* LibTomMath, multiple-precision integer library -- Tom St Denis
- *
- * LibTomMath is a library that provides multiple-precision
- * integer arithmetic as well as number theoretic functionality.
- *
- * The library is free for all purposes without any express
- * guarantee it works.
- */
+/* LibTomMath, multiple-precision integer library -- Tom St Denis */
+/* SPDX-License-Identifier: Unlicense */
/* Tonelli-Shanks algorithm
* https://en.wikipedia.org/wiki/Tonelli%E2%80%93Shanks_algorithm
@@ -15,110 +9,110 @@
*
*/
-int mp_sqrtmod_prime(mp_int *n, mp_int *prime, mp_int *ret)
+mp_err mp_sqrtmod_prime(const mp_int *n, const mp_int *prime, mp_int *ret)
{
- int res, legendre;
- mp_int t1, C, Q, S, Z, M, T, R, two;
- mp_digit i;
+ mp_err err;
+ int legendre;
+ mp_int t1, C, Q, S, Z, M, T, R, two;
+ mp_digit i;
- /* first handle the simple cases */
- if (mp_cmp_d(n, 0) == MP_EQ) {
- mp_zero(ret);
- return MP_OKAY;
- }
- if (mp_cmp_d(prime, 2) == MP_EQ) return MP_VAL; /* prime must be odd */
- if ((res = mp_jacobi(n, prime, &legendre)) != MP_OKAY) return res;
- if (legendre == -1) return MP_VAL; /* quadratic non-residue mod prime */
+ /* first handle the simple cases */
+ if (mp_cmp_d(n, 0uL) == MP_EQ) {
+ mp_zero(ret);
+ return MP_OKAY;
+ }
+ if (mp_cmp_d(prime, 2uL) == MP_EQ) return MP_VAL; /* prime must be odd */
+ if ((err = mp_kronecker(n, prime, &legendre)) != MP_OKAY) return err;
+ if (legendre == -1) return MP_VAL; /* quadratic non-residue mod prime */
- if ((res = mp_init_multi(&t1, &C, &Q, &S, &Z, &M, &T, &R, &two, NULL)) != MP_OKAY) {
- return res;
- }
+ if ((err = mp_init_multi(&t1, &C, &Q, &S, &Z, &M, &T, &R, &two, NULL)) != MP_OKAY) {
+ return err;
+ }
- /* SPECIAL CASE: if prime mod 4 == 3
- * compute directly: res = n^(prime+1)/4 mod prime
- * Handbook of Applied Cryptography algorithm 3.36
- */
- if ((res = mp_mod_d(prime, 4, &i)) != MP_OKAY) goto cleanup;
- if (i == 3) {
- if ((res = mp_add_d(prime, 1, &t1)) != MP_OKAY) goto cleanup;
- if ((res = mp_div_2(&t1, &t1)) != MP_OKAY) goto cleanup;
- if ((res = mp_div_2(&t1, &t1)) != MP_OKAY) goto cleanup;
- if ((res = mp_exptmod(n, &t1, prime, ret)) != MP_OKAY) goto cleanup;
- res = MP_OKAY;
- goto cleanup;
- }
+ /* SPECIAL CASE: if prime mod 4 == 3
+ * compute directly: err = n^(prime+1)/4 mod prime
+ * Handbook of Applied Cryptography algorithm 3.36
+ */
+ if ((err = mp_mod_d(prime, 4uL, &i)) != MP_OKAY) goto cleanup;
+ if (i == 3u) {
+ if ((err = mp_add_d(prime, 1uL, &t1)) != MP_OKAY) goto cleanup;
+ if ((err = mp_div_2(&t1, &t1)) != MP_OKAY) goto cleanup;
+ if ((err = mp_div_2(&t1, &t1)) != MP_OKAY) goto cleanup;
+ if ((err = mp_exptmod(n, &t1, prime, ret)) != MP_OKAY) goto cleanup;
+ err = MP_OKAY;
+ goto cleanup;
+ }
- /* NOW: Tonelli-Shanks algorithm */
+ /* NOW: Tonelli-Shanks algorithm */
- /* factor out powers of 2 from prime-1, defining Q and S as: prime-1 = Q*2^S */
- if ((res = mp_copy(prime, &Q)) != MP_OKAY) goto cleanup;
- if ((res = mp_sub_d(&Q, 1, &Q)) != MP_OKAY) goto cleanup;
- /* Q = prime - 1 */
- mp_zero(&S);
- /* S = 0 */
- while (mp_iseven(&Q) != MP_NO) {
- if ((res = mp_div_2(&Q, &Q)) != MP_OKAY) goto cleanup;
- /* Q = Q / 2 */
- if ((res = mp_add_d(&S, 1, &S)) != MP_OKAY) goto cleanup;
- /* S = S + 1 */
- }
+ /* factor out powers of 2 from prime-1, defining Q and S as: prime-1 = Q*2^S */
+ if ((err = mp_copy(prime, &Q)) != MP_OKAY) goto cleanup;
+ if ((err = mp_sub_d(&Q, 1uL, &Q)) != MP_OKAY) goto cleanup;
+ /* Q = prime - 1 */
+ mp_zero(&S);
+ /* S = 0 */
+ while (MP_IS_EVEN(&Q)) {
+ if ((err = mp_div_2(&Q, &Q)) != MP_OKAY) goto cleanup;
+ /* Q = Q / 2 */
+ if ((err = mp_add_d(&S, 1uL, &S)) != MP_OKAY) goto cleanup;
+ /* S = S + 1 */
+ }
- /* find a Z such that the Legendre symbol (Z|prime) == -1 */
- if ((res = mp_set_int(&Z, 2)) != MP_OKAY) goto cleanup;
- /* Z = 2 */
- while(1) {
- if ((res = mp_jacobi(&Z, prime, &legendre)) != MP_OKAY) goto cleanup;
- if (legendre == -1) break;
- if ((res = mp_add_d(&Z, 1, &Z)) != MP_OKAY) goto cleanup;
- /* Z = Z + 1 */
- }
+ /* find a Z such that the Legendre symbol (Z|prime) == -1 */
+ mp_set_u32(&Z, 2u);
+ /* Z = 2 */
+ for (;;) {
+ if ((err = mp_kronecker(&Z, prime, &legendre)) != MP_OKAY) goto cleanup;
+ if (legendre == -1) break;
+ if ((err = mp_add_d(&Z, 1uL, &Z)) != MP_OKAY) goto cleanup;
+ /* Z = Z + 1 */
+ }
- if ((res = mp_exptmod(&Z, &Q, prime, &C)) != MP_OKAY) goto cleanup;
- /* C = Z ^ Q mod prime */
- if ((res = mp_add_d(&Q, 1, &t1)) != MP_OKAY) goto cleanup;
- if ((res = mp_div_2(&t1, &t1)) != MP_OKAY) goto cleanup;
- /* t1 = (Q + 1) / 2 */
- if ((res = mp_exptmod(n, &t1, prime, &R)) != MP_OKAY) goto cleanup;
- /* R = n ^ ((Q + 1) / 2) mod prime */
- if ((res = mp_exptmod(n, &Q, prime, &T)) != MP_OKAY) goto cleanup;
- /* T = n ^ Q mod prime */
- if ((res = mp_copy(&S, &M)) != MP_OKAY) goto cleanup;
- /* M = S */
- if ((res = mp_set_int(&two, 2)) != MP_OKAY) goto cleanup;
+ if ((err = mp_exptmod(&Z, &Q, prime, &C)) != MP_OKAY) goto cleanup;
+ /* C = Z ^ Q mod prime */
+ if ((err = mp_add_d(&Q, 1uL, &t1)) != MP_OKAY) goto cleanup;
+ if ((err = mp_div_2(&t1, &t1)) != MP_OKAY) goto cleanup;
+ /* t1 = (Q + 1) / 2 */
+ if ((err = mp_exptmod(n, &t1, prime, &R)) != MP_OKAY) goto cleanup;
+ /* R = n ^ ((Q + 1) / 2) mod prime */
+ if ((err = mp_exptmod(n, &Q, prime, &T)) != MP_OKAY) goto cleanup;
+ /* T = n ^ Q mod prime */
+ if ((err = mp_copy(&S, &M)) != MP_OKAY) goto cleanup;
+ /* M = S */
+ mp_set_u32(&two, 2u);
- res = MP_VAL;
- while (1) {
- if ((res = mp_copy(&T, &t1)) != MP_OKAY) goto cleanup;
- i = 0;
- while (1) {
- if (mp_cmp_d(&t1, 1) == MP_EQ) break;
- if ((res = mp_exptmod(&t1, &two, prime, &t1)) != MP_OKAY) goto cleanup;
- i++;
- }
- if (i == 0) {
- if ((res = mp_copy(&R, ret)) != MP_OKAY) goto cleanup;
- res = MP_OKAY;
- goto cleanup;
- }
- if ((res = mp_sub_d(&M, i, &t1)) != MP_OKAY) goto cleanup;
- if ((res = mp_sub_d(&t1, 1, &t1)) != MP_OKAY) goto cleanup;
- if ((res = mp_exptmod(&two, &t1, prime, &t1)) != MP_OKAY) goto cleanup;
- /* t1 = 2 ^ (M - i - 1) */
- if ((res = mp_exptmod(&C, &t1, prime, &t1)) != MP_OKAY) goto cleanup;
- /* t1 = C ^ (2 ^ (M - i - 1)) mod prime */
- if ((res = mp_sqrmod(&t1, prime, &C)) != MP_OKAY) goto cleanup;
- /* C = (t1 * t1) mod prime */
- if ((res = mp_mulmod(&R, &t1, prime, &R)) != MP_OKAY) goto cleanup;
- /* R = (R * t1) mod prime */
- if ((res = mp_mulmod(&T, &C, prime, &T)) != MP_OKAY) goto cleanup;
- /* T = (T * C) mod prime */
- mp_set(&M, i);
- /* M = i */
- }
+ for (;;) {
+ if ((err = mp_copy(&T, &t1)) != MP_OKAY) goto cleanup;
+ i = 0;
+ for (;;) {
+ if (mp_cmp_d(&t1, 1uL) == MP_EQ) break;
+ if ((err = mp_exptmod(&t1, &two, prime, &t1)) != MP_OKAY) goto cleanup;
+ i++;
+ }
+ if (i == 0u) {
+ if ((err = mp_copy(&R, ret)) != MP_OKAY) goto cleanup;
+ err = MP_OKAY;
+ goto cleanup;
+ }
+ if ((err = mp_sub_d(&M, i, &t1)) != MP_OKAY) goto cleanup;
+ if ((err = mp_sub_d(&t1, 1uL, &t1)) != MP_OKAY) goto cleanup;
+ if ((err = mp_exptmod(&two, &t1, prime, &t1)) != MP_OKAY) goto cleanup;
+ /* t1 = 2 ^ (M - i - 1) */
+ if ((err = mp_exptmod(&C, &t1, prime, &t1)) != MP_OKAY) goto cleanup;
+ /* t1 = C ^ (2 ^ (M - i - 1)) mod prime */
+ if ((err = mp_sqrmod(&t1, prime, &C)) != MP_OKAY) goto cleanup;
+ /* C = (t1 * t1) mod prime */
+ if ((err = mp_mulmod(&R, &t1, prime, &R)) != MP_OKAY) goto cleanup;
+ /* R = (R * t1) mod prime */
+ if ((err = mp_mulmod(&T, &C, prime, &T)) != MP_OKAY) goto cleanup;
+ /* T = (T * C) mod prime */
+ mp_set(&M, i);
+ /* M = i */
+ }
cleanup:
- mp_clear_multi(&t1, &C, &Q, &S, &Z, &M, &T, &R, &two, NULL);
- return res;
+ mp_clear_multi(&t1, &C, &Q, &S, &Z, &M, &T, &R, &two, NULL);
+ return err;
}
#endif
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