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aa6bb135 RS |
1 | /* |
2 | * Copyright 1995-2016 The OpenSSL Project Authors. All Rights Reserved. | |
0f113f3e | 3 | * |
aa6bb135 RS |
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 | |
d02b48c6 RE |
8 | */ |
9 | ||
0f113f3e MC |
10 | /* |
11 | * NB: These functions have been upgraded - the previous prototypes are in | |
12 | * dh_depr.c as wrappers to these ones. - Geoff | |
e9224c71 GT |
13 | */ |
14 | ||
d02b48c6 | 15 | #include <stdio.h> |
b39fc560 | 16 | #include "internal/cryptlib.h" |
ec577822 | 17 | #include <openssl/bn.h> |
0aeddcfa | 18 | #include "dh_locl.h" |
71fa4513 | 19 | |
0f113f3e MC |
20 | static int dh_builtin_genparams(DH *ret, int prime_len, int generator, |
21 | BN_GENCB *cb); | |
0e4aa0d2 | 22 | |
0f113f3e MC |
23 | int DH_generate_parameters_ex(DH *ret, int prime_len, int generator, |
24 | BN_GENCB *cb) | |
25 | { | |
26 | if (ret->meth->generate_params) | |
27 | return ret->meth->generate_params(ret, prime_len, generator, cb); | |
28 | return dh_builtin_genparams(ret, prime_len, generator, cb); | |
29 | } | |
0e4aa0d2 | 30 | |
1d97c843 TH |
31 | /*- |
32 | * We generate DH parameters as follows | |
d02b48c6 RE |
33 | * find a prime q which is prime_len/2 bits long. |
34 | * p=(2*q)+1 or (p-1)/2 = q | |
35 | * For this case, g is a generator if | |
36 | * g^((p-1)/q) mod p != 1 for values of q which are the factors of p-1. | |
37 | * Since the factors of p-1 are q and 2, we just need to check | |
38 | * g^2 mod p != 1 and g^q mod p != 1. | |
39 | * | |
40 | * Having said all that, | |
41 | * there is another special case method for the generators 2, 3 and 5. | |
42 | * for 2, p mod 24 == 11 | |
4486d0cd | 43 | * for 3, p mod 12 == 5 <<<<< does not work for safe primes. |
d02b48c6 RE |
44 | * for 5, p mod 10 == 3 or 7 |
45 | * | |
46 | * Thanks to Phil Karn <karn@qualcomm.com> for the pointers about the | |
47 | * special generators and for answering some of my questions. | |
48 | * | |
49 | * I've implemented the second simple method :-). | |
4486d0cd | 50 | * Since DH should be using a safe prime (both p and q are prime), |
d02b48c6 RE |
51 | * this generator function can take a very very long time to run. |
52 | */ | |
0f113f3e MC |
53 | /* |
54 | * Actually there is no reason to insist that 'generator' be a generator. | |
82652aaf BM |
55 | * It's just as OK (and in some sense better) to use a generator of the |
56 | * order-q subgroup. | |
57 | */ | |
0f113f3e MC |
58 | static int dh_builtin_genparams(DH *ret, int prime_len, int generator, |
59 | BN_GENCB *cb) | |
60 | { | |
61 | BIGNUM *t1, *t2; | |
62 | int g, ok = -1; | |
63 | BN_CTX *ctx = NULL; | |
d02b48c6 | 64 | |
0f113f3e MC |
65 | ctx = BN_CTX_new(); |
66 | if (ctx == NULL) | |
67 | goto err; | |
68 | BN_CTX_start(ctx); | |
69 | t1 = BN_CTX_get(ctx); | |
70 | t2 = BN_CTX_get(ctx); | |
71 | if (t1 == NULL || t2 == NULL) | |
72 | goto err; | |
e9224c71 | 73 | |
0f113f3e MC |
74 | /* Make sure 'ret' has the necessary elements */ |
75 | if (!ret->p && ((ret->p = BN_new()) == NULL)) | |
76 | goto err; | |
77 | if (!ret->g && ((ret->g = BN_new()) == NULL)) | |
78 | goto err; | |
79 | ||
80 | if (generator <= 1) { | |
81 | DHerr(DH_F_DH_BUILTIN_GENPARAMS, DH_R_BAD_GENERATOR); | |
82 | goto err; | |
83 | } | |
84 | if (generator == DH_GENERATOR_2) { | |
85 | if (!BN_set_word(t1, 24)) | |
86 | goto err; | |
87 | if (!BN_set_word(t2, 11)) | |
88 | goto err; | |
89 | g = 2; | |
dfb56425 | 90 | } else if (generator == DH_GENERATOR_5) { |
0f113f3e MC |
91 | if (!BN_set_word(t1, 10)) |
92 | goto err; | |
93 | if (!BN_set_word(t2, 3)) | |
94 | goto err; | |
95 | /* | |
96 | * BN_set_word(t3,7); just have to miss out on these ones :-( | |
97 | */ | |
98 | g = 5; | |
99 | } else { | |
100 | /* | |
101 | * in the general case, don't worry if 'generator' is a generator or | |
102 | * not: since we are using safe primes, it will generate either an | |
103 | * order-q or an order-2q group, which both is OK | |
104 | */ | |
105 | if (!BN_set_word(t1, 2)) | |
106 | goto err; | |
107 | if (!BN_set_word(t2, 1)) | |
108 | goto err; | |
109 | g = generator; | |
110 | } | |
111 | ||
112 | if (!BN_generate_prime_ex(ret->p, prime_len, 1, t1, t2, cb)) | |
113 | goto err; | |
114 | if (!BN_GENCB_call(cb, 3, 0)) | |
115 | goto err; | |
116 | if (!BN_set_word(ret->g, g)) | |
117 | goto err; | |
118 | ok = 1; | |
119 | err: | |
120 | if (ok == -1) { | |
121 | DHerr(DH_F_DH_BUILTIN_GENPARAMS, ERR_R_BN_LIB); | |
122 | ok = 0; | |
123 | } | |
d02b48c6 | 124 | |
0f113f3e MC |
125 | if (ctx != NULL) { |
126 | BN_CTX_end(ctx); | |
127 | BN_CTX_free(ctx); | |
128 | } | |
129 | return ok; | |
130 | } |