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#include <tommath.h>
#ifdef BN_MP_PRIME_RANDOM_EX_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 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@gmail.com, http://libtom.org
*/
/* makes a truly random prime of a given size (bits),
*
* Flags are as follows:
*
* LTM_PRIME_BBS - make prime congruent to 3 mod 4
* LTM_PRIME_SAFE - make sure (p-1)/2 is prime as well (implies LTM_PRIME_BBS)
* LTM_PRIME_2MSB_OFF - make the 2nd highest bit zero
* LTM_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! */
int mp_prime_random_ex(mp_int *a, int t, int size, int flags, ltm_prime_callback cb, void *dat)
{
unsigned char *tmp, maskAND, maskOR_msb, maskOR_lsb;
int res, err, bsize, maskOR_msb_offset;
/* sanity check the input */
if (size <= 1 || t <= 0) {
return MP_VAL;
}
/* LTM_PRIME_SAFE implies LTM_PRIME_BBS */
if (flags & LTM_PRIME_SAFE) {
flags |= LTM_PRIME_BBS;
}
/* calc the byte size */
bsize = (size>>3) + ((size&7)?1:0);
/* we need a buffer of bsize bytes */
tmp = OPT_CAST(unsigned char) XMALLOC(bsize);
if (tmp == NULL) {
return MP_MEM;
}
/* calc the maskAND value for the MSbyte*/
maskAND = ((size&7) == 0) ? 0xFF : (0xFF >> (8 - (size & 7)));
/* calc the maskOR_msb */
maskOR_msb = 0;
maskOR_msb_offset = ((size & 7) == 1) ? 1 : 0;
if (flags & LTM_PRIME_2MSB_ON) {
maskOR_msb |= 0x80 >> ((9 - size) & 7);
}
/* get the maskOR_lsb */
maskOR_lsb = 1;
if (flags & LTM_PRIME_BBS) {
maskOR_lsb |= 3;
}
do {
/* read the bytes */
if (cb(tmp, bsize, dat) != bsize) {
err = MP_VAL;
goto error;
}
/* work over the MSbyte */
tmp[0] &= maskAND;
tmp[0] |= 1 << ((size - 1) & 7);
/* mix in the maskORs */
tmp[maskOR_msb_offset] |= maskOR_msb;
tmp[bsize-1] |= maskOR_lsb;
/* read it in */
if ((err = mp_read_unsigned_bin(a, tmp, bsize)) != MP_OKAY) { goto error; }
/* is it prime? */
if ((err = mp_prime_is_prime(a, t, &res)) != MP_OKAY) { goto error; }
if (res == MP_NO) {
continue;
}
if (flags & LTM_PRIME_SAFE) {
/* see if (a-1)/2 is prime */
if ((err = mp_sub_d(a, 1, a)) != MP_OKAY) { goto error; }
if ((err = mp_div_2(a, a)) != MP_OKAY) { goto error; }
/* is it prime? */
if ((err = mp_prime_is_prime(a, t, &res)) != MP_OKAY) { goto error; }
}
} while (res == MP_NO);
if (flags & LTM_PRIME_SAFE) {
/* restore a to the original value */
if ((err = mp_mul_2(a, a)) != MP_OKAY) { goto error; }
if ((err = mp_add_d(a, 1, a)) != MP_OKAY) { goto error; }
}
err = MP_OKAY;
error:
XFREE(tmp);
return err;
}
#endif
/* $Source: /cvs/libtom/libtommath/bn_mp_prime_random_ex.c,v $ */
/* $Revision: 1.5 $ */
/* $Date: 2006/12/28 01:25:13 $ */
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