genrsa.c revision 29698e296e3fd1474a362fbd229bca888175bb66 
1/*
2 * Dropbear - a SSH2 server
3 *
4 * Copyright (c) 2002,2003 Matt Johnston
5 * All rights reserved.
6 *
7 * Permission is hereby granted, free of charge, to any person obtaining a copy
8 * of this software and associated documentation files (the "Software"), to deal
9 * in the Software without restriction, including without limitation the rights
10 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
11 * copies of the Software, and to permit persons to whom the Software is
12 * furnished to do so, subject to the following conditions:
13 *
14 * The above copyright notice and this permission notice shall be included in
15 * all copies or substantial portions of the Software.
16 *
17 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
18 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
19 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
20 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
21 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
22 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
23 * SOFTWARE. */
24
25#include "includes.h"
26#include "dbutil.h"
27#include "bignum.h"
28#include "random.h"
29#include "rsa.h"
30#include "genrsa.h"
31
32#define RSA_E 65537
33
34#ifdef DROPBEAR_RSA
35
36static void getrsaprime(mp_int* prime, mp_int *primeminus,
37		mp_int* rsa_e, unsigned int size);
38
39/* mostly taken from libtomcrypt's rsa key generation routine */
40rsa_key * gen_rsa_priv_key(unsigned int size) {
41
42	rsa_key * key;
43	DEF_MP_INT(pminus);
44	DEF_MP_INT(qminus);
45	DEF_MP_INT(lcm);
46
47	key = (rsa_key*)m_malloc(sizeof(rsa_key));
48
49	key->e = (mp_int*)m_malloc(sizeof(mp_int));
50	key->n = (mp_int*)m_malloc(sizeof(mp_int));
51	key->d = (mp_int*)m_malloc(sizeof(mp_int));
52	key->p = (mp_int*)m_malloc(sizeof(mp_int));
53	key->q = (mp_int*)m_malloc(sizeof(mp_int));
54
55	m_mp_init_multi(key->e, key->n, key->d, key->p, key->q,
56			&pminus, &lcm, &qminus, NULL);
57
58	seedrandom();
59
60	if (mp_set_int(key->e, RSA_E) != MP_OKAY) {
61		fprintf(stderr, "rsa generation failed\n");
62		exit(1);
63	}
64
65	/* PuTTY doesn't like it if the modulus isn't a multiple of 8 bits,
66	 * so we just generate them until we get one which is OK */
67	getrsaprime(key->p, &pminus, key->e, size/2);
68	do {
69		getrsaprime(key->q, &qminus, key->e, size/2);
70
71		if (mp_mul(key->p, key->q, key->n) != MP_OKAY) {
72			fprintf(stderr, "rsa generation failed\n");
73			exit(1);
74		}
75	} while (mp_count_bits(key->n) % 8 != 0);
76
77	/* lcm(p-1, q-1) */
78	if (mp_lcm(&pminus, &qminus, &lcm) != MP_OKAY) {
79		fprintf(stderr, "rsa generation failed\n");
80		exit(1);
81	}
82
83	/* de = 1 mod lcm(p-1,q-1) */
84	/* therefore d = (e^-1) mod lcm(p-1,q-1) */
85	if (mp_invmod(key->e, &lcm, key->d) != MP_OKAY) {
86		fprintf(stderr, "rsa generation failed\n");
87		exit(1);
88	}
89
90	mp_clear_multi(&pminus, &qminus, &lcm, NULL);
91
92	return key;
93}
94
95/* return a prime suitable for p or q */
96static void getrsaprime(mp_int* prime, mp_int *primeminus,
97		mp_int* rsa_e, unsigned int size) {
98
99	unsigned char *buf;
100	DEF_MP_INT(temp_gcd);
101
102	buf = (unsigned char*)m_malloc(size+1);
103
104	m_mp_init(&temp_gcd);
105	do {
106		/* generate a random odd number with MSB set, then find the
107		   the next prime above it */
108		genrandom(buf, size+1);
109		buf[0] |= 0x80; /* MSB set */
110
111		bytes_to_mp(prime, buf, size+1);
112
113		/* find the next integer which is prime, 8 round of miller-rabin */
114		if (mp_prime_next_prime(prime, 8, 0) != MP_OKAY) {
115			fprintf(stderr, "rsa generation failed\n");
116			exit(1);
117		}
118
119		/* subtract one to get p-1 */
120		if (mp_sub_d(prime, 1, primeminus) != MP_OKAY) {
121			fprintf(stderr, "rsa generation failed\n");
122			exit(1);
123		}
124		/* check relative primality to e */
125		if (mp_gcd(primeminus, rsa_e, &temp_gcd) != MP_OKAY) {
126			fprintf(stderr, "rsa generation failed\n");
127			exit(1);
128		}
129	} while (mp_cmp_d(&temp_gcd, 1) != MP_EQ); /* while gcd(p-1, e) != 1 */
130
131	/* now we have a good value for result */
132	mp_clear(&temp_gcd);
133	m_burn(buf, size+1);
134	m_free(buf);
135}
136
137#endif /* DROPBEAR_RSA */
138