crypto/dh/dh_gen.c

   1 /*
   2  * Copyright 1995-2020 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 "dh_local.h"
  32
  33 #ifndef FIPS_MODULE
  34 static int dh_builtin_genparams(DH *ret, int prime_len, int generator,
  35                                 BN_GENCB *cb);
  36 #endif /* FIPS_MODULE */
  37
  38 int dh_generate_ffc_parameters(DH *dh, int type, int pbits, int qbits,
  39                                BN_GENCB *cb)
  40 {
  41     int ret, res;
  42
  43 #ifndef FIPS_MODULE
  44     if (type == DH_PARAMGEN_TYPE_FIPS_186_2)
  45         ret = ossl_ffc_params_FIPS186_2_generate(dh->libctx, &dh->params,
  46                                                  FFC_PARAM_TYPE_DH,
  47                                                  pbits, qbits, &res, cb);
  48     else
  49 #endif
  50         ret = ossl_ffc_params_FIPS186_4_generate(dh->libctx, &dh->params,
  51                                                  FFC_PARAM_TYPE_DH,
  52                                                  pbits, qbits, &res, cb);
  53     if (ret > 0)
  54         dh->dirty_cnt++;
  55     return ret;
  56 }
  57
  58 int dh_get_named_group_uid_from_size(int pbits)
  59 {
  60     /*
  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.
  66      */
  67     int nid;
  68
  69     switch (pbits) {
  70     case 2048:
  71         nid = NID_ffdhe2048;
  72         break;
  73     case 3072:
  74         nid = NID_ffdhe3072;
  75         break;
  76     case 4096:
  77         nid = NID_ffdhe4096;
  78         break;
  79     case 6144:
  80         nid = NID_ffdhe6144;
  81         break;
  82     case 8192:
  83         nid = NID_ffdhe8192;
  84         break;
  85     /* unsupported prime_len */
  86     default:
  87         return NID_undef;
  88     }
  89     return nid;
  90 }
  91
  92 #ifdef FIPS_MODULE
  93
  94 static int dh_gen_named_group(OSSL_LIB_CTX *libctx, DH *ret, int prime_len)
  95 {
  96     DH *dh;
  97     int ok = 0;
  98     int nid = dh_get_named_group_uid_from_size(prime_len);
  99
 100     if (nid == NID_undef)
 101         return 0;
 102
 103     dh = dh_new_by_nid_ex(libctx, nid);
 104     if (dh != NULL
 105         && ossl_ffc_params_copy(&ret->params, &dh->params)) {
 106         ok = 1;
 107         ret->dirty_cnt++;
 108     }
 109     DH_free(dh);
 110     return ok;
 111 }
 112 #endif /* FIPS_MODULE */
 113
 114 int DH_generate_parameters_ex(DH *ret, int prime_len, int generator,
 115                               BN_GENCB *cb)
 116 {
 117 #ifdef FIPS_MODULE
 118     if (generator != 2)
 119         return 0;
 120     return dh_gen_named_group(ret->libctx, ret, prime_len);
 121 #else
 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 */
 126 }
 127
 128 #ifndef FIPS_MODULE
 129 /*-
 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
 136  * g^q mod p == 1.
 137  * Or in terms of the Legendre symbol: (g/p) == 1.
 138  *
 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
 147  *
 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
 154  */
 155 static int dh_builtin_genparams(DH *ret, int prime_len, int generator,
 156                                 BN_GENCB *cb)
 157 {
 158     BIGNUM *t1, *t2;
 159     int g, ok = -1;
 160     BN_CTX *ctx = NULL;
 161
 162     if (prime_len > OPENSSL_DH_MAX_MODULUS_BITS) {
 163         ERR_raise(ERR_LIB_DH, DH_R_MODULUS_TOO_LARGE);
 164         return 0;
 165     }
 166
 167     if (prime_len < DH_MIN_MODULUS_BITS) {
 168         ERR_raise(ERR_LIB_DH, DH_R_MODULUS_TOO_SMALL);
 169         return 0;
 170     }
 171
 172     ctx = BN_CTX_new();
 173     if (ctx == NULL)
 174         goto err;
 175     BN_CTX_start(ctx);
 176     t1 = BN_CTX_get(ctx);
 177     t2 = BN_CTX_get(ctx);
 178     if (t2 == NULL)
 179         goto err;
 180
 181     /* Make sure 'ret' has the necessary elements */
 182     if (ret->params.p == NULL && ((ret->params.p = BN_new()) == NULL))
 183         goto err;
 184     if (ret->params.g == NULL && ((ret->params.g = BN_new()) == NULL))
 185         goto err;
 186
 187     if (generator <= 1) {
 188         ERR_raise(ERR_LIB_DH, DH_R_BAD_GENERATOR);
 189         goto err;
 190     }
 191     if (generator == DH_GENERATOR_2) {
 192         if (!BN_set_word(t1, 24))
 193             goto err;
 194         if (!BN_set_word(t2, 23))
 195             goto err;
 196         g = 2;
 197     } else if (generator == DH_GENERATOR_5) {
 198         if (!BN_set_word(t1, 60))
 199             goto err;
 200         if (!BN_set_word(t2, 59))
 201             goto err;
 202         g = 5;
 203     } else {
 204         /*
 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
 208          */
 209         if (!BN_set_word(t1, 12))
 210             goto err;
 211         if (!BN_set_word(t2, 11))
 212             goto err;
 213         g = generator;
 214     }
 215
 216     if (!BN_generate_prime_ex(ret->params.p, prime_len, 1, t1, t2, cb))
 217         goto err;
 218     if (!BN_GENCB_call(cb, 3, 0))
 219         goto err;
 220     if (!BN_set_word(ret->params.g, g))
 221         goto err;
 222     ret->dirty_cnt++;
 223     ok = 1;
 224  err:
 225     if (ok == -1) {
 226         ERR_raise(ERR_LIB_DH, ERR_R_BN_LIB);
 227         ok = 0;
 228     }
 229
 230     BN_CTX_end(ctx);
 231     BN_CTX_free(ctx);
 232     return ok;
 233 }
 234 #endif /* FIPS_MODULE */