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comparison libtomcrypt/src/pk/dsa/dsa_make_key.c @ 399:a707e6148060

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merge of '5fdf69ca60d1683cdd9f4c2595134bed26394834' and '6b61c50f4cf888bea302ac8fcf5dbb573b443251'
author Matt Johnston <matt@ucc.asn.au>
date Sat, 03 Feb 2007 08:20:34 +0000
parents 0cbe8f6dbf9e
children f849a5ca2efc
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394:17d097fc111c 399:a707e6148060
1 /* LibTomCrypt, modular cryptographic library -- Tom St Denis
2 *
3 * LibTomCrypt is a library that provides various cryptographic
4 * algorithms in a highly modular and flexible manner.
5 *
6 * The library is free for all purposes without any express
7 * guarantee it works.
8 *
9 * Tom St Denis, [email protected], http://libtomcrypt.com
10 */
11 #include "tomcrypt.h"
12
13 /**
14 @file dsa_make_key.c
15 DSA implementation, generate a DSA key, Tom St Denis
16 */
17
18 #ifdef MDSA
19
20 /**
21 Create a DSA key
22 @param prng An active PRNG state
23 @param wprng The index of the PRNG desired
24 @param group_size Size of the multiplicative group (octets)
25 @param modulus_size Size of the modulus (octets)
26 @param key [out] Where to store the created key
27 @return CRYPT_OK if successful, upon error this function will free all allocated memory
28 */
29 int dsa_make_key(prng_state *prng, int wprng, int group_size, int modulus_size, dsa_key *key)
30 {
31 void *tmp, *tmp2;
32 int err, res;
33 unsigned char *buf;
34
35 LTC_ARGCHK(key != NULL);
36 LTC_ARGCHK(ltc_mp.name != NULL);
37
38 /* check prng */
39 if ((err = prng_is_valid(wprng)) != CRYPT_OK) {
40 return err;
41 }
42
43 /* check size */
44 if (group_size >= MDSA_MAX_GROUP || group_size <= 15 ||
45 group_size >= modulus_size || (modulus_size - group_size) >= MDSA_DELTA) {
46 return CRYPT_INVALID_ARG;
47 }
48
49 /* allocate ram */
50 buf = XMALLOC(MDSA_DELTA);
51 if (buf == NULL) {
52 return CRYPT_MEM;
53 }
54
55 /* init mp_ints */
56 if ((err = mp_init_multi(&tmp, &tmp2, &key->g, &key->q, &key->p, &key->x, &key->y, NULL)) != CRYPT_OK) {
57 XFREE(buf);
58 return err;
59 }
60
61 /* make our prime q */
62 if ((err = rand_prime(key->q, group_size, prng, wprng)) != CRYPT_OK) { goto error; }
63
64 /* double q */
65 if ((err = mp_add(key->q, key->q, tmp)) != CRYPT_OK) { goto error; }
66
67 /* now make a random string and multply it against q */
68 if (prng_descriptor[wprng].read(buf+1, modulus_size - group_size, prng) != (unsigned long)(modulus_size - group_size)) {
69 err = CRYPT_ERROR_READPRNG;
70 goto error;
71 }
72
73 /* force magnitude */
74 buf[0] |= 0xC0;
75
76 /* force even */
77 buf[modulus_size - group_size - 1] &= ~1;
78
79 if ((err = mp_read_unsigned_bin(tmp2, buf, modulus_size - group_size)) != CRYPT_OK) { goto error; }
80 if ((err = mp_mul(key->q, tmp2, key->p)) != CRYPT_OK) { goto error; }
81 if ((err = mp_add_d(key->p, 1, key->p)) != CRYPT_OK) { goto error; }
82
83 /* now loop until p is prime */
84 for (;;) {
85 if ((err = mp_prime_is_prime(key->p, 8, &res)) != CRYPT_OK) { goto error; }
86 if (res == LTC_MP_YES) break;
87
88 /* add 2q to p and 2 to tmp2 */
89 if ((err = mp_add(tmp, key->p, key->p)) != CRYPT_OK) { goto error; }
90 if ((err = mp_add_d(tmp2, 2, tmp2)) != CRYPT_OK) { goto error; }
91 }
92
93 /* now p = (q * tmp2) + 1 is prime, find a value g for which g^tmp2 != 1 */
94 mp_set(key->g, 1);
95
96 do {
97 if ((err = mp_add_d(key->g, 1, key->g)) != CRYPT_OK) { goto error; }
98 if ((err = mp_exptmod(key->g, tmp2, key->p, tmp)) != CRYPT_OK) { goto error; }
99 } while (mp_cmp_d(tmp, 1) == LTC_MP_EQ);
100
101 /* at this point tmp generates a group of order q mod p */
102 mp_exch(tmp, key->g);
103
104 /* so now we have our DH structure, generator g, order q, modulus p
105 Now we need a random exponent [mod q] and it's power g^x mod p
106 */
107 do {
108 if (prng_descriptor[wprng].read(buf, group_size, prng) != (unsigned long)group_size) {
109 err = CRYPT_ERROR_READPRNG;
110 goto error;
111 }
112 if ((err = mp_read_unsigned_bin(key->x, buf, group_size)) != CRYPT_OK) { goto error; }
113 } while (mp_cmp_d(key->x, 1) != LTC_MP_GT);
114 if ((err = mp_exptmod(key->g, key->x, key->p, key->y)) != CRYPT_OK) { goto error; }
115
116 key->type = PK_PRIVATE;
117 key->qord = group_size;
118
119 #ifdef LTC_CLEAN_STACK
120 zeromem(buf, MDSA_DELTA);
121 #endif
122
123 err = CRYPT_OK;
124 goto done;
125 error:
126 mp_clear_multi(key->g, key->q, key->p, key->x, key->y, NULL);
127 done:
128 mp_clear_multi(tmp, tmp2, NULL);
129 XFREE(buf);
130 return err;
131 }
132
133 #endif
134
135 /* $Source: /cvs/libtom/libtomcrypt/src/pk/dsa/dsa_make_key.c,v $ */
136 /* $Revision: 1.10 $ */
137 /* $Date: 2006/12/04 03:18:43 $ */