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