2 * Copyright 1995-2020 The OpenSSL Project Authors. All Rights Reserved.
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
11 * NB: These functions have been upgraded - the previous prototypes are in
12 * dh_depr.c as wrappers to these ones. - Geoff
16 * DH low level APIs are deprecated for public use, but still ok for
19 * NOTE: When generating keys for key-agreement schemes - FIPS 140-2 IG 9.9
20 * states that no additional pairwise tests are required (apart from the tests
21 * specified in SP800-56A) when generating keys. Hence DH pairwise tests are
24 #include "internal/deprecated.h"
27 #include "internal/cryptlib.h"
28 #include <openssl/bn.h>
29 #include <openssl/sha.h>
30 #include "crypto/dh.h"
34 static int dh_builtin_genparams(DH *ret, int prime_len, int generator,
36 #endif /* FIPS_MODULE */
38 int dh_generate_ffc_parameters(DH *dh, int type, int pbits,
39 int qbits, EVP_MD *md, BN_GENCB *cb)
45 qbits = EVP_MD_size(md) * 8;
47 qbits = (pbits >= 2048 ? SHA256_DIGEST_LENGTH :
48 SHA_DIGEST_LENGTH) * 8;
51 if (type == DH_PARAMGEN_TYPE_FIPS_186_2)
52 ret = ffc_params_FIPS186_2_generate(dh->libctx, &dh->params,
54 pbits, qbits, md, &res, cb);
57 ret = ffc_params_FIPS186_4_generate(dh->libctx, &dh->params,
59 pbits, qbits, md, &res, cb);
65 int dh_get_named_group_uid_from_size(int pbits)
68 * Just choose an approved safe prime group.
69 * The alternative to this is to generate FIPS186-4 domain parameters i.e.
70 * return dh_generate_ffc_parameters(ret, prime_len, 0, NULL, cb);
71 * As the FIPS186-4 generated params are for backwards compatibility,
72 * the safe prime group should be used as the default.
92 /* unsupported prime_len */
101 static int dh_gen_named_group(OPENSSL_CTX *libctx, DH *ret, int prime_len)
105 int nid = dh_get_named_group_uid_from_size(prime_len);
107 if (nid == NID_undef)
110 dh = dh_new_by_nid_with_libctx(libctx, nid);
112 && ffc_params_copy(&ret->params, &dh->params)) {
119 #endif /* FIPS_MODULE */
121 int DH_generate_parameters_ex(DH *ret, int prime_len, int generator,
127 return dh_gen_named_group(ret->libctx, ret, prime_len);
129 if (ret->meth->generate_params)
130 return ret->meth->generate_params(ret, prime_len, generator, cb);
131 return dh_builtin_genparams(ret, prime_len, generator, cb);
132 #endif /* FIPS_MODULE */
137 * We generate DH parameters as follows
138 * find a prime p which is prime_len bits long,
139 * where q=(p-1)/2 is also prime.
140 * In the following we assume that g is not 0, 1 or p-1, since it
141 * would generate only trivial subgroups.
142 * For this case, g is a generator of the order-q subgroup if
144 * Or in terms of the Legendre symbol: (g/p) == 1.
146 * Having said all that,
147 * there is another special case method for the generators 2, 3 and 5.
148 * Using the quadratic reciprocity law it is possible to solve
149 * (g/p) == 1 for the special values 2, 3, 5:
150 * (2/p) == 1 if p mod 8 == 1 or 7.
151 * (3/p) == 1 if p mod 12 == 1 or 11.
152 * (5/p) == 1 if p mod 5 == 1 or 4.
153 * See for instance: https://en.wikipedia.org/wiki/Legendre_symbol
155 * Since all safe primes > 7 must satisfy p mod 12 == 11
156 * and all safe primes > 11 must satisfy p mod 5 != 1
157 * we can further improve the condition for g = 2, 3 and 5:
158 * for 2, p mod 24 == 23
159 * for 3, p mod 12 == 11
160 * for 5, p mod 60 == 59
162 static int dh_builtin_genparams(DH *ret, int prime_len, int generator,
169 if (prime_len > OPENSSL_DH_MAX_MODULUS_BITS) {
170 DHerr(DH_F_DH_BUILTIN_GENPARAMS, DH_R_MODULUS_TOO_LARGE);
174 if (prime_len < DH_MIN_MODULUS_BITS) {
175 DHerr(DH_F_DH_BUILTIN_GENPARAMS, DH_R_MODULUS_TOO_SMALL);
183 t1 = BN_CTX_get(ctx);
184 t2 = BN_CTX_get(ctx);
188 /* Make sure 'ret' has the necessary elements */
189 if (ret->params.p == NULL && ((ret->params.p = BN_new()) == NULL))
191 if (ret->params.g == NULL && ((ret->params.g = BN_new()) == NULL))
194 if (generator <= 1) {
195 DHerr(DH_F_DH_BUILTIN_GENPARAMS, DH_R_BAD_GENERATOR);
198 if (generator == DH_GENERATOR_2) {
199 if (!BN_set_word(t1, 24))
201 if (!BN_set_word(t2, 23))
204 } else if (generator == DH_GENERATOR_5) {
205 if (!BN_set_word(t1, 60))
207 if (!BN_set_word(t2, 59))
212 * in the general case, don't worry if 'generator' is a generator or
213 * not: since we are using safe primes, it will generate either an
214 * order-q or an order-2q group, which both is OK
216 if (!BN_set_word(t1, 12))
218 if (!BN_set_word(t2, 11))
223 if (!BN_generate_prime_ex(ret->params.p, prime_len, 1, t1, t2, cb))
225 if (!BN_GENCB_call(cb, 3, 0))
227 if (!BN_set_word(ret->params.g, g))
233 DHerr(DH_F_DH_BUILTIN_GENPARAMS, ERR_R_BN_LIB);
241 #endif /* FIPS_MODULE */