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/* rsa-keygen.c
*
* Generation of RSA keypairs
*/
/* nettle, low-level cryptographics library
*
* Copyright (C) 2002 Niels Möller
*
* The nettle library is free software; you can redistribute it and/or modify
* it under the terms of the GNU Lesser General Public License as published by
* the Free Software Foundation; either version 2.1 of the License, or (at your
* option) any later version.
*
* The nettle library is distributed in the hope that it will be useful, but
* WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
* or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public
* License for more details.
*
* You should have received a copy of the GNU Lesser General Public License
* along with the nettle library; see the file COPYING.LIB. If not, write to
* the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
* MA 02111-1307, USA.
*/
#if HAVE_CONFIG_H
# include "config.h"
#endif
#include <assert.h>
#include <stdlib.h>
#include "rsa.h"
#include "bignum.h"
#ifndef DEBUG
# define DEBUG 0
#endif
#if DEBUG
# include <stdio.h>
#endif
/* Returns a random prime of size BITS */
static void
bignum_random_prime(mpz_t x, unsigned bits,
void *random_ctx, nettle_random_func random,
void *progress_ctx, nettle_progress_func progress)
{
assert(bits);
for (;;)
{
nettle_mpz_random_size(x, random_ctx, random, bits);
mpz_setbit(x, bits - 1);
/* Miller-rabin count of 25 is probably much overkill. */
nettle_next_prime(x, x, 25, 10000, progress_ctx, progress);
if (mpz_sizeinbase(x, 2) == bits)
break;
}
}
int
rsa_generate_keypair(struct rsa_public_key *pub,
struct rsa_private_key *key,
void *random_ctx, nettle_random_func random,
void *progress_ctx, nettle_progress_func progress,
unsigned n_size,
unsigned e_size)
{
mpz_t p1;
mpz_t q1;
mpz_t phi;
mpz_t tmp;
if (e_size)
{
/* We should choose e randomly. Is the size reasonable? */
if ((e_size < 16) || (e_size > n_size) )
return 0;
}
else
{
/* We have a fixed e. Check that it makes sense */
/* It must be odd */
if (!mpz_tstbit(pub->e, 0))
return 0;
/* And 3 or larger */
if (mpz_cmp_ui(pub->e, 3) < 0)
return 0;
}
if (n_size < RSA_MINIMUM_N_BITS)
return 0;
mpz_init(p1); mpz_init(q1); mpz_init(phi); mpz_init(tmp);
/* Generate primes */
for (;;)
{
/* Generate p, such that gcd(p-1, e) = 1 */
for (;;)
{
bignum_random_prime(key->p, (n_size+1)/2,
random_ctx, random,
progress_ctx, progress);
mpz_sub_ui(p1, key->p, 1);
/* If e was given, we must chose p such that p-1 has no factors in
* common with e. */
if (e_size)
break;
mpz_gcd(tmp, pub->e, p1);
if (mpz_cmp_ui(tmp, 1) == 0)
break;
else if (progress) progress(progress_ctx, 'c');
}
if (progress)
progress(progress_ctx, '\n');
/* Generate q, such that gcd(q-1, e) = 1 */
for (;;)
{
bignum_random_prime(key->q, n_size/2,
random_ctx, random,
progress_ctx, progress);
mpz_sub_ui(q1, key->q, 1);
/* If e was given, we must chose q such that q-1 has no factors in
* common with e. */
if (e_size)
break;
mpz_gcd(tmp, pub->e, q1);
if (mpz_cmp_ui(tmp, 1) == 0)
break;
else if (progress) progress(progress_ctx, 'c');
}
/* Now we have the primes. Is the product of the right size? */
mpz_mul(pub->n, key->p, key->q);
if (mpz_sizeinbase(pub->n, 2) != n_size)
/* We might get an n of size n_size-1. Then just try again. */
{
#if DEBUG
fprintf(stderr,
"\nWanted size: %d, p-size: %d, q-size: %d, n-size: %d\n",
n_size,
mpz_sizeinbase(key->p,2),
mpz_sizeinbase(key->q,2),
mpz_sizeinbase(pub->n,2));
#endif
if (progress)
{
progress(progress_ctx, 'b');
progress(progress_ctx, '\n');
}
continue;
}
if (progress)
progress(progress_ctx, '\n');
/* c = q^{-1} (mod p) */
if (mpz_invert(key->c, key->q, key->p))
/* This should succeed everytime. But if it doesn't,
* we try again. */
break;
else if (progress) progress(progress_ctx, '?');
}
mpz_mul(phi, p1, q1);
/* If we didn't have a given e, generate one now. */
if (e_size)
{
int retried = 0;
for (;;)
{
nettle_mpz_random_size(pub->e,
random_ctx, random,
e_size);
/* Make sure it's odd and that the most significant bit is
* set */
mpz_setbit(pub->e, 0);
mpz_setbit(pub->e, e_size - 1);
/* Needs gmp-3, or inverse might be negative. */
if (mpz_invert(key->d, pub->e, phi))
break;
if (progress) progress(progress_ctx, 'e');
retried = 1;
}
if (retried && progress)
progress(progress_ctx, '\n');
}
else
{
/* Must always succeed, as we already that e
* doesn't have any common factor with p-1 or q-1. */
int res = mpz_invert(key->d, pub->e, phi);
assert(res);
}
/* Done! Almost, we must compute the auxillary private values. */
/* a = d % (p-1) */
mpz_fdiv_r(key->a, key->d, p1);
/* b = d % (q-1) */
mpz_fdiv_r(key->b, key->d, q1);
/* c was computed earlier */
pub->size = key->size = (mpz_sizeinbase(pub->n, 2) + 7) / 8;
assert(pub->size >= RSA_MINIMUM_N_OCTETS);
mpz_clear(p1); mpz_clear(q1); mpz_clear(phi); mpz_clear(tmp);
return 1;
}
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