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/* LibTomCrypt, modular cryptographic library -- Tom St Denis
*
* LibTomCrypt is a library that provides various cryptographic
* algorithms in a highly modular and flexible manner.
*
* The library is free for all purposes without any express
* guarantee it works.
*
* Tom St Denis, tomstdenis@gmail.com, http://libtom.org
*/
#include "tomcrypt.h"
/**
@file rand_prime.c
Generate a random prime, Tom St Denis
*/
#define USE_BBS 1
int rand_prime(mp_int * N, long len)
{
int err, res, type;
unsigned char *buf;
LTC_ARGCHK(N != NULL);
/* get type */
if (len < 0) {
type = USE_BBS;
len = -len;
} else {
type = 0;
}
/* allow sizes between 2 and 512 bytes for a prime size */
if (len < 2 || len > 512) {
return CRYPT_INVALID_PRIME_SIZE;
}
/* allocate buffer to work with */
buf = XCALLOC(1, len);
if (buf == NULL) {
return CRYPT_MEM;
}
do {
/* generate value */
get_random_bytes(buf, len);
/* munge bits */
buf[0] |= 0x80 | 0x40;
buf[len - 1] |= 0x01 | ((type & USE_BBS) ? 0x02 : 0x00);
/* load value */
if ((err = mp_read_unsigned_bin(N, buf, len)) != CRYPT_OK) {
XFREE(buf);
return err;
}
/* test */
if ((err = mp_prime_is_prime(N, 8, &res)) != CRYPT_OK) {
XFREE(buf);
return err;
}
} while (res == LTC_MP_NO);
#ifdef LTC_CLEAN_STACK
zeromem(buf, len);
#endif
XFREE(buf);
return CRYPT_OK;
}
/* $Source: /cvs/libtom/libtomcrypt/src/math/rand_prime.c,v $ */
/* $Revision: 1.7 $ */
/* $Date: 2006/12/28 01:27:23 $ */
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