2 * Copyright 1995-2021 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"
31 #include "crypto/security_bits.h"
35 static int dh_builtin_genparams(DH *ret, int prime_len, int generator,
37 #endif /* FIPS_MODULE */
39 int ossl_dh_generate_ffc_parameters(DH *dh, int type, int pbits, int qbits,
45 if (type == DH_PARAMGEN_TYPE_FIPS_186_2)
46 ret = ossl_ffc_params_FIPS186_2_generate(dh->libctx, &dh->params,
48 pbits, qbits, &res, cb);
51 ret = ossl_ffc_params_FIPS186_4_generate(dh->libctx, &dh->params,
53 pbits, qbits, &res, cb);
59 int ossl_dh_get_named_group_uid_from_size(int pbits)
62 * Just choose an approved safe prime group.
63 * The alternative to this is to generate FIPS186-4 domain parameters i.e.
64 * return dh_generate_ffc_parameters(ret, prime_len, 0, NULL, cb);
65 * As the FIPS186-4 generated params are for backwards compatibility,
66 * the safe prime group should be used as the default.
86 /* unsupported prime_len */
95 static int dh_gen_named_group(OSSL_LIB_CTX *libctx, DH *ret, int prime_len)
99 int nid = ossl_dh_get_named_group_uid_from_size(prime_len);
101 if (nid == NID_undef)
104 dh = ossl_dh_new_by_nid_ex(libctx, nid);
106 && ossl_ffc_params_copy(&ret->params, &dh->params)) {
113 #endif /* FIPS_MODULE */
115 int DH_generate_parameters_ex(DH *ret, int prime_len, int generator,
121 return dh_gen_named_group(ret->libctx, ret, prime_len);
123 if (ret->meth->generate_params)
124 return ret->meth->generate_params(ret, prime_len, generator, cb);
125 return dh_builtin_genparams(ret, prime_len, generator, cb);
126 #endif /* FIPS_MODULE */
131 * We generate DH parameters as follows
132 * find a prime p which is prime_len bits long,
133 * where q=(p-1)/2 is also prime.
134 * In the following we assume that g is not 0, 1 or p-1, since it
135 * would generate only trivial subgroups.
136 * For this case, g is a generator of the order-q subgroup if
138 * Or in terms of the Legendre symbol: (g/p) == 1.
140 * Having said all that,
141 * there is another special case method for the generators 2, 3 and 5.
142 * Using the quadratic reciprocity law it is possible to solve
143 * (g/p) == 1 for the special values 2, 3, 5:
144 * (2/p) == 1 if p mod 8 == 1 or 7.
145 * (3/p) == 1 if p mod 12 == 1 or 11.
146 * (5/p) == 1 if p mod 5 == 1 or 4.
147 * See for instance: https://en.wikipedia.org/wiki/Legendre_symbol
149 * Since all safe primes > 7 must satisfy p mod 12 == 11
150 * and all safe primes > 11 must satisfy p mod 5 != 1
151 * we can further improve the condition for g = 2, 3 and 5:
152 * for 2, p mod 24 == 23
153 * for 3, p mod 12 == 11
154 * for 5, p mod 60 == 59
156 static int dh_builtin_genparams(DH *ret, int prime_len, int generator,
163 if (prime_len > OPENSSL_DH_MAX_MODULUS_BITS) {
164 ERR_raise(ERR_LIB_DH, DH_R_MODULUS_TOO_LARGE);
168 if (prime_len < DH_MIN_MODULUS_BITS) {
169 ERR_raise(ERR_LIB_DH, DH_R_MODULUS_TOO_SMALL);
173 ctx = BN_CTX_new_ex(ret->libctx);
177 t1 = BN_CTX_get(ctx);
178 t2 = BN_CTX_get(ctx);
182 /* Make sure 'ret' has the necessary elements */
183 if (ret->params.p == NULL && ((ret->params.p = BN_new()) == NULL))
185 if (ret->params.g == NULL && ((ret->params.g = BN_new()) == NULL))
188 if (generator <= 1) {
189 ERR_raise(ERR_LIB_DH, DH_R_BAD_GENERATOR);
192 if (generator == DH_GENERATOR_2) {
193 if (!BN_set_word(t1, 24))
195 if (!BN_set_word(t2, 23))
198 } else if (generator == DH_GENERATOR_5) {
199 if (!BN_set_word(t1, 60))
201 if (!BN_set_word(t2, 59))
206 * in the general case, don't worry if 'generator' is a generator or
207 * not: since we are using safe primes, it will generate either an
208 * order-q or an order-2q group, which both is OK
210 if (!BN_set_word(t1, 12))
212 if (!BN_set_word(t2, 11))
217 if (!BN_generate_prime_ex2(ret->params.p, prime_len, 1, t1, t2, cb, ctx))
219 if (!BN_GENCB_call(cb, 3, 0))
221 if (!BN_set_word(ret->params.g, g))
223 /* We are using safe prime p, set key length equivalent to RFC 7919 */
224 ret->length = (2 * ossl_ifc_ffc_compute_security_bits(prime_len)
230 ERR_raise(ERR_LIB_DH, ERR_R_BN_LIB);
238 #endif /* FIPS_MODULE */