4fcb168fa840e5155d564b99175a5e0eb7156680
[strongswan.git] / src / libstrongswan / plugins / gmp / gmp_diffie_hellman.c
1 /*
2 * Copyright (C) 1998-2002 D. Hugh Redelmeier.
3 * Copyright (C) 1999, 2000, 2001 Henry Spencer.
4 * Copyright (C) 2010 Tobias Brunner
5 * Copyright (C) 2005-2008 Martin Willi
6 * Copyright (C) 2005 Jan Hutter
7 * Hochschule fuer Technik Rapperswil
8 *
9 * This program is free software; you can redistribute it and/or modify it
10 * under the terms of the GNU General Public License as published by the
11 * Free Software Foundation; either version 2 of the License, or (at your
12 * option) any later version. See <http://www.fsf.org/copyleft/gpl.txt>.
13 *
14 * This program is distributed in the hope that it will be useful, but
15 * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
16 * or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
17 * for more details.
18 */
19
20 #include <gmp.h>
21
22 #include "gmp_diffie_hellman.h"
23
24 #include <utils/debug.h>
25
26 #ifdef HAVE_MPZ_POWM_SEC
27 # undef mpz_powm
28 # define mpz_powm mpz_powm_sec
29 #endif
30
31 typedef struct private_gmp_diffie_hellman_t private_gmp_diffie_hellman_t;
32
33 /**
34 * Private data of an gmp_diffie_hellman_t object.
35 */
36 struct private_gmp_diffie_hellman_t {
37 /**
38 * Public gmp_diffie_hellman_t interface.
39 */
40 gmp_diffie_hellman_t public;
41
42 /**
43 * Diffie Hellman group number.
44 */
45 diffie_hellman_group_t group;
46
47 /*
48 * Generator value.
49 */
50 mpz_t g;
51
52 /**
53 * My private value.
54 */
55 mpz_t xa;
56
57 /**
58 * My public value.
59 */
60 mpz_t ya;
61
62 /**
63 * Other public value.
64 */
65 mpz_t yb;
66
67 /**
68 * Shared secret.
69 */
70 mpz_t zz;
71
72 /**
73 * Modulus.
74 */
75 mpz_t p;
76
77 /**
78 * Modulus length.
79 */
80 size_t p_len;
81
82 /**
83 * True if shared secret is computed and stored in my_public_value.
84 */
85 bool computed;
86 };
87
88 METHOD(diffie_hellman_t, set_other_public_value, bool,
89 private_gmp_diffie_hellman_t *this, chunk_t value)
90 {
91 mpz_t p_min_1;
92
93 if (!diffie_hellman_verify_value(this->group, value))
94 {
95 return FALSE;
96 }
97
98 mpz_init(p_min_1);
99 mpz_sub_ui(p_min_1, this->p, 1);
100
101 mpz_import(this->yb, value.len, 1, 1, 1, 0, value.ptr);
102
103 /* check public value:
104 * 1. 0 or 1 is invalid as 0^a = 0 and 1^a = 1
105 * 2. a public value larger or equal the modulus is invalid */
106 if (mpz_cmp_ui(this->yb, 1) > 0 &&
107 mpz_cmp(this->yb, p_min_1) < 0)
108 {
109 #ifdef EXTENDED_DH_TEST
110 /* 3. test if y ^ q mod p = 1, where q = (p - 1)/2. */
111 mpz_t q, one;
112 diffie_hellman_params_t *params;
113
114 mpz_init(q);
115 mpz_init(one);
116
117 params = diffie_hellman_get_params(this->group);
118 if (!params->subgroup.len)
119 {
120 mpz_fdiv_q_2exp(q, p_min_1, 1);
121 }
122 else
123 {
124 mpz_import(q, params->subgroup.len, 1, 1, 1, 0, params->subgroup.ptr);
125 }
126 mpz_powm(one, this->yb, q, this->p);
127 mpz_clear(q);
128 if (mpz_cmp_ui(one, 1) == 0)
129 {
130 mpz_powm(this->zz, this->yb, this->xa, this->p);
131 this->computed = TRUE;
132 }
133 else
134 {
135 DBG1(DBG_LIB, "public DH value verification failed:"
136 " y ^ q mod p != 1");
137 }
138 mpz_clear(one);
139 #else
140 mpz_powm(this->zz, this->yb, this->xa, this->p);
141 this->computed = TRUE;
142 #endif
143 }
144 else
145 {
146 DBG1(DBG_LIB, "public DH value verification failed:"
147 " y < 2 || y > p - 1 ");
148 }
149 mpz_clear(p_min_1);
150 return this->computed;
151 }
152
153 METHOD(diffie_hellman_t, get_my_public_value, bool,
154 private_gmp_diffie_hellman_t *this,chunk_t *value)
155 {
156 value->len = this->p_len;
157 value->ptr = mpz_export(NULL, NULL, 1, value->len, 1, 0, this->ya);
158 if (value->ptr == NULL)
159 {
160 value->len = 0;
161 }
162 return TRUE;
163 }
164
165 METHOD(diffie_hellman_t, get_shared_secret, bool,
166 private_gmp_diffie_hellman_t *this, chunk_t *secret)
167 {
168 if (!this->computed)
169 {
170 return FALSE;
171 }
172 secret->len = this->p_len;
173 secret->ptr = mpz_export(NULL, NULL, 1, secret->len, 1, 0, this->zz);
174 if (secret->ptr == NULL)
175 {
176 return FALSE;
177 }
178 return TRUE;
179 }
180
181 METHOD(diffie_hellman_t, get_dh_group, diffie_hellman_group_t,
182 private_gmp_diffie_hellman_t *this)
183 {
184 return this->group;
185 }
186
187 METHOD(diffie_hellman_t, destroy, void,
188 private_gmp_diffie_hellman_t *this)
189 {
190 mpz_clear(this->p);
191 mpz_clear(this->xa);
192 mpz_clear(this->ya);
193 mpz_clear(this->yb);
194 mpz_clear(this->zz);
195 mpz_clear(this->g);
196 free(this);
197 }
198
199 /**
200 * Generic internal constructor
201 */
202 static gmp_diffie_hellman_t *create_generic(diffie_hellman_group_t group,
203 size_t exp_len, chunk_t g, chunk_t p)
204 {
205 private_gmp_diffie_hellman_t *this;
206 chunk_t random;
207 rng_t *rng;
208
209 INIT(this,
210 .public = {
211 .dh = {
212 .get_shared_secret = _get_shared_secret,
213 .set_other_public_value = _set_other_public_value,
214 .get_my_public_value = _get_my_public_value,
215 .get_dh_group = _get_dh_group,
216 .destroy = _destroy,
217 },
218 },
219 .group = group,
220 .p_len = p.len,
221 );
222
223 mpz_init(this->p);
224 mpz_init(this->yb);
225 mpz_init(this->ya);
226 mpz_init(this->xa);
227 mpz_init(this->zz);
228 mpz_init(this->g);
229 mpz_import(this->g, g.len, 1, 1, 1, 0, g.ptr);
230 mpz_import(this->p, p.len, 1, 1, 1, 0, p.ptr);
231
232 rng = lib->crypto->create_rng(lib->crypto, RNG_STRONG);
233 if (!rng)
234 {
235 DBG1(DBG_LIB, "no RNG found for quality %N", rng_quality_names,
236 RNG_STRONG);
237 destroy(this);
238 return NULL;
239 }
240 if (!rng->allocate_bytes(rng, exp_len, &random))
241 {
242 DBG1(DBG_LIB, "failed to allocate DH secret");
243 rng->destroy(rng);
244 destroy(this);
245 return NULL;
246 }
247 rng->destroy(rng);
248
249 if (exp_len == this->p_len)
250 {
251 /* achieve bitsof(p)-1 by setting MSB to 0 */
252 *random.ptr &= 0x7F;
253 }
254 mpz_import(this->xa, random.len, 1, 1, 1, 0, random.ptr);
255 chunk_clear(&random);
256 DBG2(DBG_LIB, "size of DH secret exponent: %u bits",
257 mpz_sizeinbase(this->xa, 2));
258
259 mpz_powm(this->ya, this->g, this->xa, this->p);
260
261 return &this->public;
262 }
263
264 /*
265 * Described in header.
266 */
267 gmp_diffie_hellman_t *gmp_diffie_hellman_create(diffie_hellman_group_t group)
268 {
269 diffie_hellman_params_t *params;
270
271 params = diffie_hellman_get_params(group);
272 if (!params)
273 {
274 return NULL;
275 }
276 return create_generic(group, params->exp_len,
277 params->generator, params->prime);
278 }
279
280
281 gmp_diffie_hellman_t *gmp_diffie_hellman_create_custom(
282 diffie_hellman_group_t group, chunk_t g, chunk_t p)
283 {
284 if (group == MODP_CUSTOM)
285 {
286 return create_generic(MODP_CUSTOM, p.len, g, p);
287 }
288 return NULL;
289 }