126 lines
4.1 KiB
C
126 lines
4.1 KiB
C
#include "tommath_private.h"
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#ifdef MP_PRIME_FROBENIUS_UNDERWOOD_C
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/* LibTomMath, multiple-precision integer library -- Tom St Denis */
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/* SPDX-License-Identifier: Unlicense */
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/*
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* See file mp_prime_is_prime.c or the documentation in doc/bn.tex for the details
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*/
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#ifndef LTM_USE_ONLY_MR
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/*
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* floor of positive solution of
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* (2^16)-1 = (a+4)*(2*a+5)
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* TODO: Both values are smaller than N^(1/4), would have to use a bigint
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* for a instead but any a biger than about 120 are already so rare that
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* it is possible to ignore them and still get enough pseudoprimes.
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* But it is still a restriction of the set of available pseudoprimes
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* which makes this implementation less secure if used stand-alone.
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*/
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#define LTM_FROBENIUS_UNDERWOOD_A 32764
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mp_err mp_prime_frobenius_underwood(const mp_int *N, mp_bool *result)
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{
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mp_int T1z, T2z, Np1z, sz, tz;
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int a, ap2, length, i, j;
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mp_err err;
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*result = MP_NO;
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if ((err = mp_init_multi(&T1z, &T2z, &Np1z, &sz, &tz, NULL)) != MP_OKAY) {
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return err;
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}
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for (a = 0; a < LTM_FROBENIUS_UNDERWOOD_A; a++) {
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/* TODO: That's ugly! No, really, it is! */
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if ((a==2) || (a==4) || (a==7) || (a==8) || (a==10) ||
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(a==14) || (a==18) || (a==23) || (a==26) || (a==28)) {
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continue;
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}
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mp_set_i32(&T1z, (int32_t)((a * a) - 4));
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if ((err = mp_kronecker(&T1z, N, &j)) != MP_OKAY) goto LBL_FU_ERR;
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if (j == -1) {
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break;
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}
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if (j == 0) {
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/* composite */
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goto LBL_FU_ERR;
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}
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}
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/* Tell it a composite and set return value accordingly */
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if (a >= LTM_FROBENIUS_UNDERWOOD_A) {
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err = MP_ITER;
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goto LBL_FU_ERR;
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}
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/* Composite if N and (a+4)*(2*a+5) are not coprime */
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mp_set_u32(&T1z, (uint32_t)((a+4)*((2*a)+5)));
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if ((err = mp_gcd(N, &T1z, &T1z)) != MP_OKAY) goto LBL_FU_ERR;
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if (!((T1z.used == 1) && (T1z.dp[0] == 1u))) goto LBL_FU_ERR;
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ap2 = a + 2;
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if ((err = mp_add_d(N, 1uL, &Np1z)) != MP_OKAY) goto LBL_FU_ERR;
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mp_set(&sz, 1uL);
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mp_set(&tz, 2uL);
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length = mp_count_bits(&Np1z);
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for (i = length - 2; i >= 0; i--) {
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/*
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* temp = (sz*(a*sz+2*tz))%N;
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* tz = ((tz-sz)*(tz+sz))%N;
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* sz = temp;
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*/
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if ((err = mp_mul_2(&tz, &T2z)) != MP_OKAY) goto LBL_FU_ERR;
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/* a = 0 at about 50% of the cases (non-square and odd input) */
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if (a != 0) {
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if ((err = mp_mul_d(&sz, (mp_digit)a, &T1z)) != MP_OKAY) goto LBL_FU_ERR;
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if ((err = mp_add(&T1z, &T2z, &T2z)) != MP_OKAY) goto LBL_FU_ERR;
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}
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if ((err = mp_mul(&T2z, &sz, &T1z)) != MP_OKAY) goto LBL_FU_ERR;
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if ((err = mp_sub(&tz, &sz, &T2z)) != MP_OKAY) goto LBL_FU_ERR;
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if ((err = mp_add(&sz, &tz, &sz)) != MP_OKAY) goto LBL_FU_ERR;
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if ((err = mp_mul(&sz, &T2z, &tz)) != MP_OKAY) goto LBL_FU_ERR;
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if ((err = mp_mod(&tz, N, &tz)) != MP_OKAY) goto LBL_FU_ERR;
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if ((err = mp_mod(&T1z, N, &sz)) != MP_OKAY) goto LBL_FU_ERR;
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if (s_mp_get_bit(&Np1z, (unsigned int)i) == MP_YES) {
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/*
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* temp = (a+2) * sz + tz
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* tz = 2 * tz - sz
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* sz = temp
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*/
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if (a == 0) {
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if ((err = mp_mul_2(&sz, &T1z)) != MP_OKAY) goto LBL_FU_ERR;
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} else {
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if ((err = mp_mul_d(&sz, (mp_digit)ap2, &T1z)) != MP_OKAY) goto LBL_FU_ERR;
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}
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if ((err = mp_add(&T1z, &tz, &T1z)) != MP_OKAY) goto LBL_FU_ERR;
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if ((err = mp_mul_2(&tz, &T2z)) != MP_OKAY) goto LBL_FU_ERR;
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if ((err = mp_sub(&T2z, &sz, &tz)) != MP_OKAY) goto LBL_FU_ERR;
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mp_exch(&sz, &T1z);
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}
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}
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mp_set_u32(&T1z, (uint32_t)((2 * a) + 5));
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if ((err = mp_mod(&T1z, N, &T1z)) != MP_OKAY) goto LBL_FU_ERR;
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if (MP_IS_ZERO(&sz) && (mp_cmp(&tz, &T1z) == MP_EQ)) {
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*result = MP_YES;
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}
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LBL_FU_ERR:
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mp_clear_multi(&tz, &sz, &Np1z, &T2z, &T1z, NULL);
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return err;
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}
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#endif
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#endif
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