crypto/dh/dh_gen.c

   1 /*
   2  * Copyright 1995-2021 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  * 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
  22  * omitted here.
  23  */
  24 #include "internal/deprecated.h"
  25
  26 #include <stdio.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"
  32 #include "dh_local.h"
  33
  34 #ifndef FIPS_MODULE
  35 static int dh_builtin_genparams(DH *ret, int prime_len, int generator,
  36                                 BN_GENCB *cb);
  37 #endif /* FIPS_MODULE */
  38
  39 int ossl_dh_generate_ffc_parameters(DH *dh, int type, int pbits, int qbits,
  40                                     BN_GENCB *cb)
  41 {
  42     int ret, res;
  43
  44 #ifndef FIPS_MODULE
  45     if (type == DH_PARAMGEN_TYPE_FIPS_186_2)
  46         ret = ossl_ffc_params_FIPS186_2_generate(dh->libctx, &dh->params,
  47                                                  FFC_PARAM_TYPE_DH,
  48                                                  pbits, qbits, &res, cb);
  49     else
  50 #endif
  51         ret = ossl_ffc_params_FIPS186_4_generate(dh->libctx, &dh->params,
  52                                                  FFC_PARAM_TYPE_DH,
  53                                                  pbits, qbits, &res, cb);
  54     if (ret > 0)
  55         dh->dirty_cnt++;
  56     return ret;
  57 }
  58
  59 int ossl_dh_get_named_group_uid_from_size(int pbits)
  60 {
  61     /*
  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.
  67      */
  68     int nid;
  69
  70     switch (pbits) {
  71     case 2048:
  72         nid = NID_ffdhe2048;
  73         break;
  74     case 3072:
  75         nid = NID_ffdhe3072;
  76         break;
  77     case 4096:
  78         nid = NID_ffdhe4096;
  79         break;
  80     case 6144:
  81         nid = NID_ffdhe6144;
  82         break;
  83     case 8192:
  84         nid = NID_ffdhe8192;
  85         break;
  86     /* unsupported prime_len */
  87     default:
  88         return NID_undef;
  89     }
  90     return nid;
  91 }
  92
  93 #ifdef FIPS_MODULE
  94
  95 static int dh_gen_named_group(OSSL_LIB_CTX *libctx, DH *ret, int prime_len)
  96 {
  97     DH *dh;
  98     int ok = 0;
  99     int nid = ossl_dh_get_named_group_uid_from_size(prime_len);
 100
 101     if (nid == NID_undef)
 102         return 0;
 103
 104     dh = ossl_dh_new_by_nid_ex(libctx, nid);
 105     if (dh != NULL
 106         && ossl_ffc_params_copy(&ret->params, &dh->params)) {
 107         ok = 1;
 108         ret->dirty_cnt++;
 109     }
 110     DH_free(dh);
 111     return ok;
 112 }
 113 #endif /* FIPS_MODULE */
 114
 115 int DH_generate_parameters_ex(DH *ret, int prime_len, int generator,
 116                               BN_GENCB *cb)
 117 {
 118 #ifdef FIPS_MODULE
 119     if (generator != 2)
 120         return 0;
 121     return dh_gen_named_group(ret->libctx, ret, prime_len);
 122 #else
 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 */
 127 }
 128
 129 #ifndef FIPS_MODULE
 130 /*-
 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
 137  * g^q mod p == 1.
 138  * Or in terms of the Legendre symbol: (g/p) == 1.
 139  *
 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
 148  *
 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
 155  */
 156 static int dh_builtin_genparams(DH *ret, int prime_len, int generator,
 157                                 BN_GENCB *cb)
 158 {
 159     BIGNUM *t1, *t2;
 160     int g, ok = -1;
 161     BN_CTX *ctx = NULL;
 162
 163     if (prime_len > OPENSSL_DH_MAX_MODULUS_BITS) {
 164         ERR_raise(ERR_LIB_DH, DH_R_MODULUS_TOO_LARGE);
 165         return 0;
 166     }
 167
 168     if (prime_len < DH_MIN_MODULUS_BITS) {
 169         ERR_raise(ERR_LIB_DH, DH_R_MODULUS_TOO_SMALL);
 170         return 0;
 171     }
 172
 173     ctx = BN_CTX_new_ex(ret->libctx);
 174     if (ctx == NULL)
 175         goto err;
 176     BN_CTX_start(ctx);
 177     t1 = BN_CTX_get(ctx);
 178     t2 = BN_CTX_get(ctx);
 179     if (t2 == NULL)
 180         goto err;
 181
 182     /* Make sure 'ret' has the necessary elements */
 183     if (ret->params.p == NULL && ((ret->params.p = BN_new()) == NULL))
 184         goto err;
 185     if (ret->params.g == NULL && ((ret->params.g = BN_new()) == NULL))
 186         goto err;
 187
 188     if (generator <= 1) {
 189         ERR_raise(ERR_LIB_DH, DH_R_BAD_GENERATOR);
 190         goto err;
 191     }
 192     if (generator == DH_GENERATOR_2) {
 193         if (!BN_set_word(t1, 24))
 194             goto err;
 195         if (!BN_set_word(t2, 23))
 196             goto err;
 197         g = 2;
 198     } else if (generator == DH_GENERATOR_5) {
 199         if (!BN_set_word(t1, 60))
 200             goto err;
 201         if (!BN_set_word(t2, 59))
 202             goto err;
 203         g = 5;
 204     } else {
 205         /*
 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
 209          */
 210         if (!BN_set_word(t1, 12))
 211             goto err;
 212         if (!BN_set_word(t2, 11))
 213             goto err;
 214         g = generator;
 215     }
 216
 217     if (!BN_generate_prime_ex2(ret->params.p, prime_len, 1, t1, t2, cb, ctx))
 218         goto err;
 219     if (!BN_GENCB_call(cb, 3, 0))
 220         goto err;
 221     if (!BN_set_word(ret->params.g, g))
 222         goto err;
 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)
 225                    + 24) / 25 * 25;
 226     ret->dirty_cnt++;
 227     ok = 1;
 228  err:
 229     if (ok == -1) {
 230         ERR_raise(ERR_LIB_DH, ERR_R_BN_LIB);
 231         ok = 0;
 232     }
 233
 234     BN_CTX_end(ctx);
 235     BN_CTX_free(ctx);
 236     return ok;
 237 }
 238 #endif /* FIPS_MODULE */