124 lines
3.3 KiB
C
124 lines
3.3 KiB
C
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#include "tommath_private.h"
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#ifdef MP_PRIME_RAND_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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/* makes a truly random prime of a given size (bits),
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*
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* Flags are as follows:
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*
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* MP_PRIME_BBS - make prime congruent to 3 mod 4
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* MP_PRIME_SAFE - make sure (p-1)/2 is prime as well (implies MP_PRIME_BBS)
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* MP_PRIME_2MSB_ON - make the 2nd highest bit one
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*
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* You have to supply a callback which fills in a buffer with random bytes. "dat" is a parameter you can
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* have passed to the callback (e.g. a state or something). This function doesn't use "dat" itself
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* so it can be NULL
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*
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*/
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/* This is possibly the mother of all prime generation functions, muahahahahaha! */
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mp_err mp_prime_rand(mp_int *a, int t, int size, int flags)
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{
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uint8_t *tmp, maskAND, maskOR_msb, maskOR_lsb;
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int bsize, maskOR_msb_offset;
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bool res;
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mp_err err;
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/* sanity check the input */
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if ((size <= 1) || (t <= 0)) {
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return MP_VAL;
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}
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/* MP_PRIME_SAFE implies MP_PRIME_BBS */
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if ((flags & MP_PRIME_SAFE) != 0) {
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flags |= MP_PRIME_BBS;
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}
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/* calc the byte size */
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bsize = (size>>3) + ((size&7)?1:0);
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/* we need a buffer of bsize bytes */
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tmp = (uint8_t *) MP_MALLOC((size_t)bsize);
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if (tmp == NULL) {
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return MP_MEM;
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}
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/* calc the maskAND value for the MSbyte*/
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maskAND = ((size&7) == 0) ? 0xFFu : (uint8_t)(0xFFu >> (8 - (size & 7)));
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/* calc the maskOR_msb */
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maskOR_msb = 0;
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maskOR_msb_offset = ((size & 7) == 1) ? 1 : 0;
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if ((flags & MP_PRIME_2MSB_ON) != 0) {
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maskOR_msb |= (uint8_t)(0x80 >> ((9 - size) & 7));
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}
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/* get the maskOR_lsb */
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maskOR_lsb = 1u;
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if ((flags & MP_PRIME_BBS) != 0) {
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maskOR_lsb |= 3u;
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}
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do {
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/* read the bytes */
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if ((err = s_mp_rand_source(tmp, (size_t)bsize)) != MP_OKAY) {
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goto LBL_ERR;
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}
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/* work over the MSbyte */
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tmp[0] &= maskAND;
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tmp[0] |= (uint8_t)(1 << ((size - 1) & 7));
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/* mix in the maskORs */
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tmp[maskOR_msb_offset] |= maskOR_msb;
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tmp[bsize-1] |= maskOR_lsb;
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/* read it in */
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/* TODO: casting only for now until all lengths have been changed to the type "size_t"*/
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if ((err = mp_from_ubin(a, tmp, (size_t)bsize)) != MP_OKAY) {
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goto LBL_ERR;
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}
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/* is it prime? */
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if ((err = mp_prime_is_prime(a, t, &res)) != MP_OKAY) {
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goto LBL_ERR;
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}
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if (!res) {
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continue;
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}
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if ((flags & MP_PRIME_SAFE) != 0) {
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/* see if (a-1)/2 is prime */
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if ((err = mp_sub_d(a, 1uL, a)) != MP_OKAY) {
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goto LBL_ERR;
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}
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if ((err = mp_div_2(a, a)) != MP_OKAY) {
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goto LBL_ERR;
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}
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/* is it prime? */
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if ((err = mp_prime_is_prime(a, t, &res)) != MP_OKAY) {
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goto LBL_ERR;
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}
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}
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} while (!res);
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if ((flags & MP_PRIME_SAFE) != 0) {
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/* restore a to the original value */
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if ((err = mp_mul_2(a, a)) != MP_OKAY) {
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goto LBL_ERR;
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}
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if ((err = mp_add_d(a, 1uL, a)) != MP_OKAY) {
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goto LBL_ERR;
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}
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}
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err = MP_OKAY;
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LBL_ERR:
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MP_FREE_BUF(tmp, (size_t)bsize);
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return err;
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}
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#endif
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