1 /*
2  * Copyright 1995-2023 The OpenSSL Project Authors. All Rights Reserved.
3  *
4  * Licensed under the OpenSSL license (the "License").  You may not use
5  * this file except in compliance with the License.  You can obtain a copy
6  * in the file LICENSE in the source distribution or at
7  * https://www.openssl.org/source/license.html
8  */
9 
10 #include <stdio.h>
11 #include "internal/cryptlib.h"
12 #include <openssl/bn.h>
13 #include "dh_local.h"
14 
15 # define DH_NUMBER_ITERATIONS_FOR_PRIME 64
16 
17 /*-
18  * Check that p and g are suitable enough
19  *
20  * p is odd
21  * 1 < g < p - 1
22  */
DH_check_params_ex(const DH * dh)23 int DH_check_params_ex(const DH *dh)
24 {
25     int errflags = 0;
26 
27     if (!DH_check_params(dh, &errflags))
28         return 0;
29 
30     if ((errflags & DH_CHECK_P_NOT_PRIME) != 0)
31         DHerr(DH_F_DH_CHECK_PARAMS_EX, DH_R_CHECK_P_NOT_PRIME);
32     if ((errflags & DH_NOT_SUITABLE_GENERATOR) != 0)
33         DHerr(DH_F_DH_CHECK_PARAMS_EX, DH_R_NOT_SUITABLE_GENERATOR);
34 
35     return errflags == 0;
36 }
37 
DH_check_params(const DH * dh,int * ret)38 int DH_check_params(const DH *dh, int *ret)
39 {
40     int ok = 0;
41     BIGNUM *tmp = NULL;
42     BN_CTX *ctx = NULL;
43 
44     *ret = 0;
45     ctx = BN_CTX_new();
46     if (ctx == NULL)
47         goto err;
48     BN_CTX_start(ctx);
49     tmp = BN_CTX_get(ctx);
50     if (tmp == NULL)
51         goto err;
52 
53     if (!BN_is_odd(dh->p))
54         *ret |= DH_CHECK_P_NOT_PRIME;
55     if (BN_is_negative(dh->g) || BN_is_zero(dh->g) || BN_is_one(dh->g))
56         *ret |= DH_NOT_SUITABLE_GENERATOR;
57     if (BN_copy(tmp, dh->p) == NULL || !BN_sub_word(tmp, 1))
58         goto err;
59     if (BN_cmp(dh->g, tmp) >= 0)
60         *ret |= DH_NOT_SUITABLE_GENERATOR;
61 
62     ok = 1;
63  err:
64     BN_CTX_end(ctx);
65     BN_CTX_free(ctx);
66     return ok;
67 }
68 
69 /*-
70  * Check that p is a safe prime and
71  * g is a suitable generator.
72  */
DH_check_ex(const DH * dh)73 int DH_check_ex(const DH *dh)
74 {
75     int errflags = 0;
76 
77     if (!DH_check(dh, &errflags))
78         return 0;
79 
80     if ((errflags & DH_NOT_SUITABLE_GENERATOR) != 0)
81         DHerr(DH_F_DH_CHECK_EX, DH_R_NOT_SUITABLE_GENERATOR);
82     if ((errflags & DH_CHECK_Q_NOT_PRIME) != 0)
83         DHerr(DH_F_DH_CHECK_EX, DH_R_CHECK_Q_NOT_PRIME);
84     if ((errflags & DH_CHECK_INVALID_Q_VALUE) != 0)
85         DHerr(DH_F_DH_CHECK_EX, DH_R_CHECK_INVALID_Q_VALUE);
86     if ((errflags & DH_CHECK_INVALID_J_VALUE) != 0)
87         DHerr(DH_F_DH_CHECK_EX, DH_R_CHECK_INVALID_J_VALUE);
88     if ((errflags & DH_UNABLE_TO_CHECK_GENERATOR) != 0)
89         DHerr(DH_F_DH_CHECK_EX, DH_R_UNABLE_TO_CHECK_GENERATOR);
90     if ((errflags & DH_CHECK_P_NOT_PRIME) != 0)
91         DHerr(DH_F_DH_CHECK_EX, DH_R_CHECK_P_NOT_PRIME);
92     if ((errflags & DH_CHECK_P_NOT_SAFE_PRIME) != 0)
93         DHerr(DH_F_DH_CHECK_EX, DH_R_CHECK_P_NOT_SAFE_PRIME);
94 
95     return errflags == 0;
96 }
97 
DH_check(const DH * dh,int * ret)98 int DH_check(const DH *dh, int *ret)
99 {
100     int ok = 0, r, q_good = 0;
101     BN_CTX *ctx = NULL;
102     BIGNUM *t1 = NULL, *t2 = NULL;
103 
104     /* Don't do any checks at all with an excessively large modulus */
105     if (BN_num_bits(dh->p) > OPENSSL_DH_CHECK_MAX_MODULUS_BITS) {
106         DHerr(DH_F_DH_CHECK, DH_R_MODULUS_TOO_LARGE);
107         *ret = DH_CHECK_P_NOT_PRIME;
108         return 0;
109     }
110 
111     if (!DH_check_params(dh, ret))
112         return 0;
113 
114     ctx = BN_CTX_new();
115     if (ctx == NULL)
116         goto err;
117     BN_CTX_start(ctx);
118     t1 = BN_CTX_get(ctx);
119     t2 = BN_CTX_get(ctx);
120     if (t2 == NULL)
121         goto err;
122 
123     if (dh->q != NULL) {
124         if (BN_ucmp(dh->p, dh->q) > 0)
125             q_good = 1;
126         else
127             *ret |= DH_CHECK_INVALID_Q_VALUE;
128     }
129 
130     if (q_good) {
131         if (BN_cmp(dh->g, BN_value_one()) <= 0)
132             *ret |= DH_NOT_SUITABLE_GENERATOR;
133         else if (BN_cmp(dh->g, dh->p) >= 0)
134             *ret |= DH_NOT_SUITABLE_GENERATOR;
135         else {
136             /* Check g^q == 1 mod p */
137             if (!BN_mod_exp(t1, dh->g, dh->q, dh->p, ctx))
138                 goto err;
139             if (!BN_is_one(t1))
140                 *ret |= DH_NOT_SUITABLE_GENERATOR;
141         }
142         r = BN_is_prime_ex(dh->q, DH_NUMBER_ITERATIONS_FOR_PRIME, ctx, NULL);
143         if (r < 0)
144             goto err;
145         if (!r)
146             *ret |= DH_CHECK_Q_NOT_PRIME;
147         /* Check p == 1 mod q  i.e. q divides p - 1 */
148         if (!BN_div(t1, t2, dh->p, dh->q, ctx))
149             goto err;
150         if (!BN_is_one(t2))
151             *ret |= DH_CHECK_INVALID_Q_VALUE;
152         if (dh->j && BN_cmp(dh->j, t1))
153             *ret |= DH_CHECK_INVALID_J_VALUE;
154     }
155 
156     r = BN_is_prime_ex(dh->p, DH_NUMBER_ITERATIONS_FOR_PRIME, ctx, NULL);
157     if (r < 0)
158         goto err;
159     if (!r)
160         *ret |= DH_CHECK_P_NOT_PRIME;
161     else if (!dh->q) {
162         if (!BN_rshift1(t1, dh->p))
163             goto err;
164         r = BN_is_prime_ex(t1, DH_NUMBER_ITERATIONS_FOR_PRIME, ctx, NULL);
165         if (r < 0)
166             goto err;
167         if (!r)
168             *ret |= DH_CHECK_P_NOT_SAFE_PRIME;
169     }
170     ok = 1;
171  err:
172     BN_CTX_end(ctx);
173     BN_CTX_free(ctx);
174     return ok;
175 }
176 
DH_check_pub_key_ex(const DH * dh,const BIGNUM * pub_key)177 int DH_check_pub_key_ex(const DH *dh, const BIGNUM *pub_key)
178 {
179     int errflags = 0;
180 
181     if (!DH_check_pub_key(dh, pub_key, &errflags))
182         return 0;
183 
184     if ((errflags & DH_CHECK_PUBKEY_TOO_SMALL) != 0)
185         DHerr(DH_F_DH_CHECK_PUB_KEY_EX, DH_R_CHECK_PUBKEY_TOO_SMALL);
186     if ((errflags & DH_CHECK_PUBKEY_TOO_LARGE) != 0)
187         DHerr(DH_F_DH_CHECK_PUB_KEY_EX, DH_R_CHECK_PUBKEY_TOO_LARGE);
188     if ((errflags & DH_CHECK_PUBKEY_INVALID) != 0)
189         DHerr(DH_F_DH_CHECK_PUB_KEY_EX, DH_R_CHECK_PUBKEY_INVALID);
190 
191     return errflags == 0;
192 }
193 
DH_check_pub_key(const DH * dh,const BIGNUM * pub_key,int * ret)194 int DH_check_pub_key(const DH *dh, const BIGNUM *pub_key, int *ret)
195 {
196     int ok = 0;
197     BIGNUM *tmp = NULL;
198     BN_CTX *ctx = NULL;
199 
200     *ret = 0;
201     ctx = BN_CTX_new();
202     if (ctx == NULL)
203         goto err;
204     BN_CTX_start(ctx);
205     tmp = BN_CTX_get(ctx);
206     if (tmp == NULL || !BN_set_word(tmp, 1))
207         goto err;
208     if (BN_cmp(pub_key, tmp) <= 0)
209         *ret |= DH_CHECK_PUBKEY_TOO_SMALL;
210     if (BN_copy(tmp, dh->p) == NULL || !BN_sub_word(tmp, 1))
211         goto err;
212     if (BN_cmp(pub_key, tmp) >= 0)
213         *ret |= DH_CHECK_PUBKEY_TOO_LARGE;
214 
215     if (dh->q != NULL) {
216         /* Check pub_key^q == 1 mod p */
217         if (!BN_mod_exp(tmp, pub_key, dh->q, dh->p, ctx))
218             goto err;
219         if (!BN_is_one(tmp))
220             *ret |= DH_CHECK_PUBKEY_INVALID;
221     }
222 
223     ok = 1;
224  err:
225     BN_CTX_end(ctx);
226     BN_CTX_free(ctx);
227     return ok;
228 }
229