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
, int qbits
,
44 if (type
== DH_PARAMGEN_TYPE_FIPS_186_2
)
45 ret
= ossl_ffc_params_FIPS186_2_generate(dh
->libctx
, &dh
->params
,
47 pbits
, qbits
, &res
, cb
);
50 ret
= ossl_ffc_params_FIPS186_4_generate(dh
->libctx
, &dh
->params
,
52 pbits
, qbits
, &res
, cb
);
58 int dh_get_named_group_uid_from_size(int pbits
)
61 * Just choose an approved safe prime group.
62 * The alternative to this is to generate FIPS186-4 domain parameters i.e.
63 * return dh_generate_ffc_parameters(ret, prime_len, 0, NULL, cb);
64 * As the FIPS186-4 generated params are for backwards compatibility,
65 * the safe prime group should be used as the default.
85 /* unsupported prime_len */
94 static int dh_gen_named_group(OSSL_LIB_CTX
*libctx
, DH
*ret
, int prime_len
)
98 int nid
= dh_get_named_group_uid_from_size(prime_len
);
100 if (nid
== NID_undef
)
103 dh
= dh_new_by_nid_ex(libctx
, nid
);
105 && ossl_ffc_params_copy(&ret
->params
, &dh
->params
)) {
112 #endif /* FIPS_MODULE */
114 int DH_generate_parameters_ex(DH
*ret
, int prime_len
, int generator
,
120 return dh_gen_named_group(ret
->libctx
, ret
, prime_len
);
122 if (ret
->meth
->generate_params
)
123 return ret
->meth
->generate_params(ret
, prime_len
, generator
, cb
);
124 return dh_builtin_genparams(ret
, prime_len
, generator
, cb
);
125 #endif /* FIPS_MODULE */
130 * We generate DH parameters as follows
131 * find a prime p which is prime_len bits long,
132 * where q=(p-1)/2 is also prime.
133 * In the following we assume that g is not 0, 1 or p-1, since it
134 * would generate only trivial subgroups.
135 * For this case, g is a generator of the order-q subgroup if
137 * Or in terms of the Legendre symbol: (g/p) == 1.
139 * Having said all that,
140 * there is another special case method for the generators 2, 3 and 5.
141 * Using the quadratic reciprocity law it is possible to solve
142 * (g/p) == 1 for the special values 2, 3, 5:
143 * (2/p) == 1 if p mod 8 == 1 or 7.
144 * (3/p) == 1 if p mod 12 == 1 or 11.
145 * (5/p) == 1 if p mod 5 == 1 or 4.
146 * See for instance: https://en.wikipedia.org/wiki/Legendre_symbol
148 * Since all safe primes > 7 must satisfy p mod 12 == 11
149 * and all safe primes > 11 must satisfy p mod 5 != 1
150 * we can further improve the condition for g = 2, 3 and 5:
151 * for 2, p mod 24 == 23
152 * for 3, p mod 12 == 11
153 * for 5, p mod 60 == 59
155 static int dh_builtin_genparams(DH
*ret
, int prime_len
, int generator
,
162 if (prime_len
> OPENSSL_DH_MAX_MODULUS_BITS
) {
163 DHerr(DH_F_DH_BUILTIN_GENPARAMS
, DH_R_MODULUS_TOO_LARGE
);
167 if (prime_len
< DH_MIN_MODULUS_BITS
) {
168 DHerr(DH_F_DH_BUILTIN_GENPARAMS
, DH_R_MODULUS_TOO_SMALL
);
176 t1
= BN_CTX_get(ctx
);
177 t2
= BN_CTX_get(ctx
);
181 /* Make sure 'ret' has the necessary elements */
182 if (ret
->params
.p
== NULL
&& ((ret
->params
.p
= BN_new()) == NULL
))
184 if (ret
->params
.g
== NULL
&& ((ret
->params
.g
= BN_new()) == NULL
))
187 if (generator
<= 1) {
188 DHerr(DH_F_DH_BUILTIN_GENPARAMS
, DH_R_BAD_GENERATOR
);
191 if (generator
== DH_GENERATOR_2
) {
192 if (!BN_set_word(t1
, 24))
194 if (!BN_set_word(t2
, 23))
197 } else if (generator
== DH_GENERATOR_5
) {
198 if (!BN_set_word(t1
, 60))
200 if (!BN_set_word(t2
, 59))
205 * in the general case, don't worry if 'generator' is a generator or
206 * not: since we are using safe primes, it will generate either an
207 * order-q or an order-2q group, which both is OK
209 if (!BN_set_word(t1
, 12))
211 if (!BN_set_word(t2
, 11))
216 if (!BN_generate_prime_ex(ret
->params
.p
, prime_len
, 1, t1
, t2
, cb
))
218 if (!BN_GENCB_call(cb
, 3, 0))
220 if (!BN_set_word(ret
->params
.g
, g
))
226 DHerr(DH_F_DH_BUILTIN_GENPARAMS
, ERR_R_BN_LIB
);
234 #endif /* FIPS_MODULE */