2 * Copyright 1995-2017 The OpenSSL Project Authors. All Rights Reserved.
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
11 * NB: These functions have been upgraded - the previous prototypes are in
12 * dh_depr.c as wrappers to these ones. - Geoff
16 #include "internal/cryptlib.h"
17 #include <openssl/bn.h>
20 static int dh_builtin_genparams(DH *ret, int prime_len, int generator,
23 int DH_generate_parameters_ex(DH *ret, int prime_len, int generator,
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);
32 * We generate DH parameters as follows
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.
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
43 * for 3, p mod 12 == 5 <<<<< does not work for safe primes.
44 * for 5, p mod 10 == 3 or 7
46 * Thanks to Phil Karn <karn@qualcomm.com> for the pointers about the
47 * special generators and for answering some of my questions.
49 * I've implemented the second simple method :-).
50 * Since DH should be using a safe prime (both p and q are prime),
51 * this generator function can take a very very long time to run.
54 * Actually there is no reason to insist that 'generator' be a generator.
55 * It's just as OK (and in some sense better) to use a generator of the
58 static int dh_builtin_genparams(DH *ret, int prime_len, int generator,
74 /* Make sure 'ret' has the necessary elements */
75 if (!ret->p && ((ret->p = BN_new()) == NULL))
77 if (!ret->g && ((ret->g = BN_new()) == NULL))
81 DHerr(DH_F_DH_BUILTIN_GENPARAMS, DH_R_BAD_GENERATOR);
84 if (generator == DH_GENERATOR_2) {
85 if (!BN_set_word(t1, 24))
87 if (!BN_set_word(t2, 11))
90 } else if (generator == DH_GENERATOR_5) {
91 if (!BN_set_word(t1, 10))
93 if (!BN_set_word(t2, 3))
96 * BN_set_word(t3,7); just have to miss out on these ones :-(
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
105 if (!BN_set_word(t1, 2))
107 if (!BN_set_word(t2, 1))
112 if (!BN_generate_prime_ex(ret->p, prime_len, 1, t1, t2, cb))
114 if (!BN_GENCB_call(cb, 3, 0))
116 if (!BN_set_word(ret->g, g))
121 DHerr(DH_F_DH_BUILTIN_GENPARAMS, ERR_R_BN_LIB);