crypto/dh/dh_gen.c

   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 /*
  16  * DH low level APIs are deprecated for public use, but still ok for
  17  * internal use.
  18  */
  19 #include "internal/deprecated.h"
  20
  21 #include <stdio.h>
  22 #include "internal/cryptlib.h"
  23 #include <openssl/bn.h>
  24 #include "crypto/dh.h"
  25 #include "dh_local.h"
  26
  27 #ifndef FIPS_MODE
  28 static int dh_builtin_genparams(DH *ret, int prime_len, int generator,
  29                                 BN_GENCB *cb);
  30 #endif /* FIPS_MODE */
  31
  32 /*
  33  * TODO(3.0): keygen should be able to use this method to do a FIPS186-4 style
  34  * paramgen.
  35  */
  36 int dh_generate_ffc_parameters(DH *dh, int bits,
  37                                int qbits, int gindex, BN_GENCB *cb)
  38 {
  39     int ret, res;
  40
  41     if (qbits <= 0) {
  42         const EVP_MD *evpmd = bits >= 2048 ? EVP_sha256() : EVP_sha1();
  43
  44         qbits = EVP_MD_size(evpmd) * 8;
  45     }
  46     dh->params.gindex = gindex;
  47     ret = ffc_params_FIPS186_4_generate(dh->libctx, &dh->params,
  48                                         FFC_PARAM_TYPE_DH,
  49                                         bits, qbits, NULL, &res, cb);
  50     if (ret > 0)
  51         dh->dirty_cnt++;
  52     return ret;
  53 }
  54
  55 int DH_generate_parameters_ex(DH *ret, int prime_len, int generator,
  56                               BN_GENCB *cb)
  57 {
  58 #ifdef FIPS_MODE
  59     /*
  60      * Just choose an approved safe prime group.
  61      * The alternative to this is to generate FIPS186-4 domain parameters i.e.
  62      * return dh_generate_ffc_parameters(ret, prime_len, -1, -1, cb);
  63      * As the FIPS186-4 generated params are for backwards compatability,
  64      * the safe prime group should be used as the default.
  65      */
  66     DH *dh = NULL;
  67     int ok = 0, nid;
  68
  69     if (generator != 2)
  70         return 0;
  71
  72     switch (prime_len) {
  73     case 2048:
  74         nid = NID_ffdhe2048;
  75         break;
  76     case 3072:
  77         nid = NID_ffdhe3072;
  78         break;
  79     case 4096:
  80         nid = NID_ffdhe4096;
  81         break;
  82     case 6144:
  83         nid = NID_ffdhe6144;
  84         break;
  85     case 8192:
  86         nid = NID_ffdhe8192;
  87         break;
  88     /* unsupported prime_len */
  89     default:
  90         return 0;
  91     }
  92     dh = DH_new_by_nid(nid);
  93     if (dh != NULL && ffc_params_copy(&ret->params, &dh->params)) {
  94         ok = 1;
  95         ret->dirty_cnt++;
  96     }
  97     DH_free(dh);
  98     return ok;
  99 #else
 100     if (ret->meth->generate_params)
 101         return ret->meth->generate_params(ret, prime_len, generator, cb);
 102     return dh_builtin_genparams(ret, prime_len, generator, cb);
 103 #endif /* FIPS_MODE */
 104 }
 105
 106 #ifndef FIPS_MODE
 107 /*-
 108  * We generate DH parameters as follows
 109  * find a prime p which is prime_len bits long,
 110  * where q=(p-1)/2 is also prime.
 111  * In the following we assume that g is not 0, 1 or p-1, since it
 112  * would generate only trivial subgroups.
 113  * For this case, g is a generator of the order-q subgroup if
 114  * g^q mod p == 1.
 115  * Or in terms of the Legendre symbol: (g/p) == 1.
 116  *
 117  * Having said all that,
 118  * there is another special case method for the generators 2, 3 and 5.
 119  * Using the quadratic reciprocity law it is possible to solve
 120  * (g/p) == 1 for the special values 2, 3, 5:
 121  * (2/p) == 1 if p mod 8 == 1 or 7.
 122  * (3/p) == 1 if p mod 12 == 1 or 11.
 123  * (5/p) == 1 if p mod 5 == 1 or 4.
 124  * See for instance: https://en.wikipedia.org/wiki/Legendre_symbol
 125  *
 126  * Since all safe primes > 7 must satisfy p mod 12 == 11
 127  * and all safe primes > 11 must satisfy p mod 5 != 1
 128  * we can further improve the condition for g = 2, 3 and 5:
 129  * for 2, p mod 24 == 23
 130  * for 3, p mod 12 == 11
 131  * for 5, p mod 60 == 59
 132  */
 133 static int dh_builtin_genparams(DH *ret, int prime_len, int generator,
 134                                 BN_GENCB *cb)
 135 {
 136     BIGNUM *t1, *t2;
 137     int g, ok = -1;
 138     BN_CTX *ctx = NULL;
 139
 140     if (prime_len > OPENSSL_DH_MAX_MODULUS_BITS) {
 141         DHerr(DH_F_DH_BUILTIN_GENPARAMS, DH_R_MODULUS_TOO_LARGE);
 142         return 0;
 143     }
 144
 145     if (prime_len < DH_MIN_MODULUS_BITS) {
 146         DHerr(DH_F_DH_BUILTIN_GENPARAMS, DH_R_MODULUS_TOO_SMALL);
 147         return 0;
 148     }
 149
 150     ctx = BN_CTX_new();
 151     if (ctx == NULL)
 152         goto err;
 153     BN_CTX_start(ctx);
 154     t1 = BN_CTX_get(ctx);
 155     t2 = BN_CTX_get(ctx);
 156     if (t2 == NULL)
 157         goto err;
 158
 159     /* Make sure 'ret' has the necessary elements */
 160     if (ret->params.p == NULL && ((ret->params.p = BN_new()) == NULL))
 161         goto err;
 162     if (ret->params.g == NULL && ((ret->params.g = BN_new()) == NULL))
 163         goto err;
 164
 165     if (generator <= 1) {
 166         DHerr(DH_F_DH_BUILTIN_GENPARAMS, DH_R_BAD_GENERATOR);
 167         goto err;
 168     }
 169     if (generator == DH_GENERATOR_2) {
 170         if (!BN_set_word(t1, 24))
 171             goto err;
 172         if (!BN_set_word(t2, 23))
 173             goto err;
 174         g = 2;
 175     } else if (generator == DH_GENERATOR_5) {
 176         if (!BN_set_word(t1, 60))
 177             goto err;
 178         if (!BN_set_word(t2, 59))
 179             goto err;
 180         g = 5;
 181     } else {
 182         /*
 183          * in the general case, don't worry if 'generator' is a generator or
 184          * not: since we are using safe primes, it will generate either an
 185          * order-q or an order-2q group, which both is OK
 186          */
 187         if (!BN_set_word(t1, 12))
 188             goto err;
 189         if (!BN_set_word(t2, 11))
 190             goto err;
 191         g = generator;
 192     }
 193
 194     if (!BN_generate_prime_ex(ret->params.p, prime_len, 1, t1, t2, cb))
 195         goto err;
 196     if (!BN_GENCB_call(cb, 3, 0))
 197         goto err;
 198     if (!BN_set_word(ret->params.g, g))
 199         goto err;
 200     ret->dirty_cnt++;
 201     ok = 1;
 202  err:
 203     if (ok == -1) {
 204         DHerr(DH_F_DH_BUILTIN_GENPARAMS, ERR_R_BN_LIB);
 205         ok = 0;
 206     }
 207
 208     BN_CTX_end(ctx);
 209     BN_CTX_free(ctx);
 210     return ok;
 211 }
 212 #endif /* FIPS_MODE */