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/* 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 was designed directly after the MPI library by
* Michael Fromberger but has been written from scratch with
* additional optimizations in place.
*
* The library is free for all purposes without any express
* guarantee it works.
*
* Tom St Denis, tomstdenis@iahu.ca, http://math.libtomcrypt.org
*/
#include <tommath.h>
/* makes a truly random prime of a given size (bytes),
* call with bbs = 1 if you want it to be congruent to 3 mod 4
*
* 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
*
* The prime generated will be larger than 2^(8*size).
*/
/* this sole function may hold the key to enslaving all mankind! */
int mp_prime_random(mp_int *a, int t, int size, int bbs, ltm_prime_callback cb, void *dat)
{
unsigned char *tmp;
int res, err;
/* sanity check the input */
if (size <= 0) {
return MP_VAL;
}
/* we need a buffer of size+1 bytes */
tmp = XMALLOC(size+1);
if (tmp == NULL) {
return MP_MEM;
}
/* fix MSB */
tmp[0] = 1;
do {
/* read the bytes */
if (cb(tmp+1, size, dat) != size) {
err = MP_VAL;
goto error;
}
/* fix the LSB */
tmp[size] |= (bbs ? 3 : 1);
/* read it in */
if ((err = mp_read_unsigned_bin(a, tmp, size+1)) != MP_OKAY) {
goto error;
}
/* is it prime? */
if ((err = mp_prime_is_prime(a, t, &res)) != MP_OKAY) {
goto error;
}
} while (res == MP_NO);
err = MP_OKAY;
error:
XFREE(tmp);
return err;
}
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