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/*
* Dropbear - a SSH2 server
*
* Copyright (c) 2002,2003 Matt Johnston
* All rights reserved.
*
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to deal
* in the Software without restriction, including without limitation the rights
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in
* all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
* SOFTWARE. */
#include "includes.h"
#include "dbutil.h"
#include "bignum.h"
#include "random.h"
#include "rsa.h"
#include "genrsa.h"
#define RSA_E 65537
#ifdef DROPBEAR_RSA
static void getrsaprime(mp_int* prime, mp_int *primeminus,
mp_int* rsa_e, unsigned int size_bytes);
/* mostly taken from libtomcrypt's rsa key generation routine */
dropbear_rsa_key * gen_rsa_priv_key(unsigned int size) {
dropbear_rsa_key * key;
DEF_MP_INT(pminus);
DEF_MP_INT(qminus);
DEF_MP_INT(lcm);
if (size < 512 || size > 4096 || (size % 8 != 0)) {
dropbear_exit("Bits must satisfy 512 <= bits <= 4096, and be a"
" multiple of 8");
}
key = m_malloc(sizeof(*key));
m_mp_alloc_init_multi(&key->e, &key->n, &key->d, &key->p, &key->q, NULL);
m_mp_init_multi(&pminus, &lcm, &qminus, NULL);
if (mp_set_int(key->e, RSA_E) != MP_OKAY) {
fprintf(stderr, "RSA generation failed\n");
exit(1);
}
getrsaprime(key->p, &pminus, key->e, size/16);
getrsaprime(key->q, &qminus, key->e, size/16);
if (mp_mul(key->p, key->q, key->n) != MP_OKAY) {
fprintf(stderr, "RSA generation failed\n");
exit(1);
}
/* lcm(p-1, q-1) */
if (mp_lcm(&pminus, &qminus, &lcm) != MP_OKAY) {
fprintf(stderr, "RSA generation failed\n");
exit(1);
}
/* de = 1 mod lcm(p-1,q-1) */
/* therefore d = (e^-1) mod lcm(p-1,q-1) */
if (mp_invmod(key->e, &lcm, key->d) != MP_OKAY) {
fprintf(stderr, "RSA generation failed\n");
exit(1);
}
mp_clear_multi(&pminus, &qminus, &lcm, NULL);
return key;
}
/* return a prime suitable for p or q */
static void getrsaprime(mp_int* prime, mp_int *primeminus,
mp_int* rsa_e, unsigned int size_bytes) {
unsigned char *buf;
DEF_MP_INT(temp_gcd);
buf = (unsigned char*)m_malloc(size_bytes+1);
m_mp_init(&temp_gcd);
do {
/* generate a random odd number with MSB set, then find the
the next prime above it */
genrandom(buf, size_bytes+1);
buf[0] |= 0x80; /* MSB set */
bytes_to_mp(prime, buf, size_bytes+1);
/* find the next integer which is prime, 8 round of miller-rabin */
if (mp_prime_next_prime(prime, 8, 0) != MP_OKAY) {
fprintf(stderr, "RSA generation failed\n");
exit(1);
}
/* subtract one to get p-1 */
if (mp_sub_d(prime, 1, primeminus) != MP_OKAY) {
fprintf(stderr, "RSA generation failed\n");
exit(1);
}
/* check relative primality to e */
if (mp_gcd(primeminus, rsa_e, &temp_gcd) != MP_OKAY) {
fprintf(stderr, "RSA generation failed\n");
exit(1);
}
} while (mp_cmp_d(&temp_gcd, 1) != MP_EQ); /* while gcd(p-1, e) != 1 */
/* now we have a good value for result */
mp_clear(&temp_gcd);
m_burn(buf, size_bytes+1);
m_free(buf);
}
#endif /* DROPBEAR_RSA */
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