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,
  39                                int qbits, EVP_MD *md, BN_GENCB *cb)
  40 {
  41     int ret, res;
  42
  43     if (qbits <= 0) {
  44         if (md != NULL)
  45             qbits = EVP_MD_size(md) * 8;
  46         else
  47             qbits = (pbits >= 2048 ? SHA256_DIGEST_LENGTH :
  48                                      SHA_DIGEST_LENGTH) * 8;
  49     }
  50 #ifndef FIPS_MODULE
  51     if (type == DH_PARAMGEN_TYPE_FIPS_186_2)
  52         ret = ffc_params_FIPS186_2_generate(dh->libctx, &dh->params,
  53                                             FFC_PARAM_TYPE_DH,
  54                                             pbits, qbits, md, &res, cb);
  55     else
  56 #endif
  57         ret = ffc_params_FIPS186_4_generate(dh->libctx, &dh->params,
  58                                             FFC_PARAM_TYPE_DH,
  59                                             pbits, qbits, md, &res, cb);
  60     if (ret > 0)
  61         dh->dirty_cnt++;
  62     return ret;
  63 }
  64
  65 int dh_get_named_group_uid_from_size(int pbits)
  66 {
  67     /*
  68      * Just choose an approved safe prime group.
  69      * The alternative to this is to generate FIPS186-4 domain parameters i.e.
  70      * return dh_generate_ffc_parameters(ret, prime_len, 0, NULL, cb);
  71      * As the FIPS186-4 generated params are for backwards compatability,
  72      * the safe prime group should be used as the default.
  73      */
  74     int nid;
  75
  76     switch (pbits) {
  77     case 2048:
  78         nid = NID_ffdhe2048;
  79         break;
  80     case 3072:
  81         nid = NID_ffdhe3072;
  82         break;
  83     case 4096:
  84         nid = NID_ffdhe4096;
  85         break;
  86     case 6144:
  87         nid = NID_ffdhe6144;
  88         break;
  89     case 8192:
  90         nid = NID_ffdhe8192;
  91         break;
  92     /* unsupported prime_len */
  93     default:
  94         return NID_undef;
  95     }
  96     return nid;
  97 }
  98
  99 #ifdef FIPS_MODULE
 100
 101 static int dh_gen_named_group(OPENSSL_CTX *libctx, DH *ret, int prime_len)
 102 {
 103     DH *dh;
 104     int ok = 0;
 105     int nid = dh_get_named_group_uid_from_size(prime_len);
 106
 107     if (nid == NID_undef)
 108         return 0;
 109
 110     dh = dh_new_by_nid_with_libctx(libctx, nid);
 111     if (dh != NULL
 112         && ffc_params_copy(&ret->params, &dh->params)) {
 113         ok = 1;
 114         ret->dirty_cnt++;
 115     }
 116     DH_free(dh);
 117     return ok;
 118 }
 119 #endif /* FIPS_MODULE */
 120
 121 int DH_generate_parameters_ex(DH *ret, int prime_len, int generator,
 122                               BN_GENCB *cb)
 123 {
 124 #ifdef FIPS_MODULE
 125     if (generator != 2)
 126         return 0;
 127     return dh_gen_named_group(ret->libctx, ret, prime_len);
 128 #else
 129     if (ret->meth->generate_params)
 130         return ret->meth->generate_params(ret, prime_len, generator, cb);
 131     return dh_builtin_genparams(ret, prime_len, generator, cb);
 132 #endif /* FIPS_MODULE */
 133 }
 134
 135 #ifndef FIPS_MODULE
 136 /*-
 137  * We generate DH parameters as follows
 138  * find a prime p which is prime_len bits long,
 139  * where q=(p-1)/2 is also prime.
 140  * In the following we assume that g is not 0, 1 or p-1, since it
 141  * would generate only trivial subgroups.
 142  * For this case, g is a generator of the order-q subgroup if
 143  * g^q mod p == 1.
 144  * Or in terms of the Legendre symbol: (g/p) == 1.
 145  *
 146  * Having said all that,
 147  * there is another special case method for the generators 2, 3 and 5.
 148  * Using the quadratic reciprocity law it is possible to solve
 149  * (g/p) == 1 for the special values 2, 3, 5:
 150  * (2/p) == 1 if p mod 8 == 1 or 7.
 151  * (3/p) == 1 if p mod 12 == 1 or 11.
 152  * (5/p) == 1 if p mod 5 == 1 or 4.
 153  * See for instance: https://en.wikipedia.org/wiki/Legendre_symbol
 154  *
 155  * Since all safe primes > 7 must satisfy p mod 12 == 11
 156  * and all safe primes > 11 must satisfy p mod 5 != 1
 157  * we can further improve the condition for g = 2, 3 and 5:
 158  * for 2, p mod 24 == 23
 159  * for 3, p mod 12 == 11
 160  * for 5, p mod 60 == 59
 161  */
 162 static int dh_builtin_genparams(DH *ret, int prime_len, int generator,
 163                                 BN_GENCB *cb)
 164 {
 165     BIGNUM *t1, *t2;
 166     int g, ok = -1;
 167     BN_CTX *ctx = NULL;
 168
 169     if (prime_len > OPENSSL_DH_MAX_MODULUS_BITS) {
 170         DHerr(DH_F_DH_BUILTIN_GENPARAMS, DH_R_MODULUS_TOO_LARGE);
 171         return 0;
 172     }
 173
 174     if (prime_len < DH_MIN_MODULUS_BITS) {
 175         DHerr(DH_F_DH_BUILTIN_GENPARAMS, DH_R_MODULUS_TOO_SMALL);
 176         return 0;
 177     }
 178
 179     ctx = BN_CTX_new();
 180     if (ctx == NULL)
 181         goto err;
 182     BN_CTX_start(ctx);
 183     t1 = BN_CTX_get(ctx);
 184     t2 = BN_CTX_get(ctx);
 185     if (t2 == NULL)
 186         goto err;
 187
 188     /* Make sure 'ret' has the necessary elements */
 189     if (ret->params.p == NULL && ((ret->params.p = BN_new()) == NULL))
 190         goto err;
 191     if (ret->params.g == NULL && ((ret->params.g = BN_new()) == NULL))
 192         goto err;
 193
 194     if (generator <= 1) {
 195         DHerr(DH_F_DH_BUILTIN_GENPARAMS, DH_R_BAD_GENERATOR);
 196         goto err;
 197     }
 198     if (generator == DH_GENERATOR_2) {
 199         if (!BN_set_word(t1, 24))
 200             goto err;
 201         if (!BN_set_word(t2, 23))
 202             goto err;
 203         g = 2;
 204     } else if (generator == DH_GENERATOR_5) {
 205         if (!BN_set_word(t1, 60))
 206             goto err;
 207         if (!BN_set_word(t2, 59))
 208             goto err;
 209         g = 5;
 210     } else {
 211         /*
 212          * in the general case, don't worry if 'generator' is a generator or
 213          * not: since we are using safe primes, it will generate either an
 214          * order-q or an order-2q group, which both is OK
 215          */
 216         if (!BN_set_word(t1, 12))
 217             goto err;
 218         if (!BN_set_word(t2, 11))
 219             goto err;
 220         g = generator;
 221     }
 222
 223     if (!BN_generate_prime_ex(ret->params.p, prime_len, 1, t1, t2, cb))
 224         goto err;
 225     if (!BN_GENCB_call(cb, 3, 0))
 226         goto err;
 227     if (!BN_set_word(ret->params.g, g))
 228         goto err;
 229     ret->dirty_cnt++;
 230     ok = 1;
 231  err:
 232     if (ok == -1) {
 233         DHerr(DH_F_DH_BUILTIN_GENPARAMS, ERR_R_BN_LIB);
 234         ok = 0;
 235     }
 236
 237     BN_CTX_end(ctx);
 238     BN_CTX_free(ctx);
 239     return ok;
 240 }
 241 #endif /* FIPS_MODULE */