1 | /* |
2 | * Copyright 1995-2019 The OpenSSL Project Authors. All Rights Reserved. |
3 | * |
4 | * Licensed under the Apache License 2.0 (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 | /* |
11 | * NB: These functions have been upgraded - the previous prototypes are in |
12 | * dh_depr.c as wrappers to these ones. - Geoff |
13 | */ |
14 | |
15 | #include <stdio.h> |
16 | #include "internal/cryptlib.h" |
17 | #include <openssl/bn.h> |
18 | #include "dh_local.h" |
19 | |
20 | static int dh_builtin_genparams(DH *ret, int prime_len, int generator, |
21 | BN_GENCB *cb); |
22 | |
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 | } |
30 | |
31 | /*- |
32 | * We generate DH parameters as follows |
33 | * find a prime p which is prime_len bits long, |
34 | * where q=(p-1)/2 is also prime. |
35 | * In the following we assume that g is not 0, 1 or p-1, since it |
36 | * would generate only trivial subgroups. |
37 | * For this case, g is a generator of the order-q subgroup if |
38 | * g^q mod p == 1. |
39 | * Or in terms of the Legendre symbol: (g/p) == 1. |
40 | * |
41 | * Having said all that, |
42 | * there is another special case method for the generators 2, 3 and 5. |
43 | * Using the quadratic reciprocity law it is possible to solve |
44 | * (g/p) == 1 for the special values 2, 3, 5: |
45 | * (2/p) == 1 if p mod 8 == 1 or 7. |
46 | * (3/p) == 1 if p mod 12 == 1 or 11. |
47 | * (5/p) == 1 if p mod 5 == 1 or 4. |
48 | * See for instance: https://en.wikipedia.org/wiki/Legendre_symbol |
49 | * |
50 | * Since all safe primes > 7 must satisfy p mod 12 == 11 |
51 | * and all safe primes > 11 must satisfy p mod 5 != 1 |
52 | * we can further improve the condition for g = 2, 3 and 5: |
53 | * for 2, p mod 24 == 23 |
54 | * for 3, p mod 12 == 11 |
55 | * for 5, p mod 60 == 59 |
56 | */ |
57 | static int dh_builtin_genparams(DH *ret, int prime_len, int generator, |
58 | BN_GENCB *cb) |
59 | { |
60 | BIGNUM *t1, *t2; |
61 | int g, ok = -1; |
62 | BN_CTX *ctx = NULL; |
63 | |
64 | if (prime_len > OPENSSL_DH_MAX_MODULUS_BITS) { |
65 | DHerr(DH_F_DH_BUILTIN_GENPARAMS, DH_R_MODULUS_TOO_LARGE); |
66 | return 0; |
67 | } |
68 | |
69 | if (prime_len < DH_MIN_MODULUS_BITS) { |
70 | DHerr(DH_F_DH_BUILTIN_GENPARAMS, DH_R_MODULUS_TOO_SMALL); |
71 | return 0; |
72 | } |
73 | |
74 | ctx = BN_CTX_new(); |
75 | if (ctx == NULL) |
76 | goto err; |
77 | BN_CTX_start(ctx); |
78 | t1 = BN_CTX_get(ctx); |
79 | t2 = BN_CTX_get(ctx); |
80 | if (t2 == NULL) |
81 | goto err; |
82 | |
83 | /* Make sure 'ret' has the necessary elements */ |
84 | if (!ret->p && ((ret->p = BN_new()) == NULL)) |
85 | goto err; |
86 | if (!ret->g && ((ret->g = BN_new()) == NULL)) |
87 | goto err; |
88 | |
89 | if (generator <= 1) { |
90 | DHerr(DH_F_DH_BUILTIN_GENPARAMS, DH_R_BAD_GENERATOR); |
91 | goto err; |
92 | } |
93 | if (generator == DH_GENERATOR_2) { |
94 | if (!BN_set_word(t1, 24)) |
95 | goto err; |
96 | if (!BN_set_word(t2, 23)) |
97 | goto err; |
98 | g = 2; |
99 | } else if (generator == DH_GENERATOR_5) { |
100 | if (!BN_set_word(t1, 60)) |
101 | goto err; |
102 | if (!BN_set_word(t2, 59)) |
103 | goto err; |
104 | g = 5; |
105 | } else { |
106 | /* |
107 | * in the general case, don't worry if 'generator' is a generator or |
108 | * not: since we are using safe primes, it will generate either an |
109 | * order-q or an order-2q group, which both is OK |
110 | */ |
111 | if (!BN_set_word(t1, 12)) |
112 | goto err; |
113 | if (!BN_set_word(t2, 11)) |
114 | goto err; |
115 | g = generator; |
116 | } |
117 | |
118 | if (!BN_generate_prime_ex(ret->p, prime_len, 1, t1, t2, cb)) |
119 | goto err; |
120 | if (!BN_GENCB_call(cb, 3, 0)) |
121 | goto err; |
122 | if (!BN_set_word(ret->g, g)) |
123 | goto err; |
124 | ret->dirty_cnt++; |
125 | ok = 1; |
126 | err: |
127 | if (ok == -1) { |
128 | DHerr(DH_F_DH_BUILTIN_GENPARAMS, ERR_R_BN_LIB); |
129 | ok = 0; |
130 | } |
131 | |
132 | BN_CTX_end(ctx); |
133 | BN_CTX_free(ctx); |
134 | return ok; |
135 | } |
136 | |