crypto/dh/dh_key.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 #include <stdio.h>
  11 #include "internal/cryptlib.h"
  12 #include "dh_locl.h"
  13 #include "crypto/bn.h"
  14
  15 static int generate_key(DH *dh);
  16 static int compute_key(unsigned char *key, const BIGNUM *pub_key, DH *dh);
  17 static int dh_bn_mod_exp(const DH *dh, BIGNUM *r,
  18                          const BIGNUM *a, const BIGNUM *p,
  19                          const BIGNUM *m, BN_CTX *ctx, BN_MONT_CTX *m_ctx);
  20 static int dh_init(DH *dh);
  21 static int dh_finish(DH *dh);
  22
  23 int DH_generate_key(DH *dh)
  24 {
  25     return dh->meth->generate_key(dh);
  26 }
  27
  28 int DH_compute_key(unsigned char *key, const BIGNUM *pub_key, DH *dh)
  29 {
  30     return dh->meth->compute_key(key, pub_key, dh);
  31 }
  32
  33 int DH_compute_key_padded(unsigned char *key, const BIGNUM *pub_key, DH *dh)
  34 {
  35     int rv, pad;
  36     rv = dh->meth->compute_key(key, pub_key, dh);
  37     if (rv <= 0)
  38         return rv;
  39     pad = BN_num_bytes(dh->p) - rv;
  40     if (pad > 0) {
  41         memmove(key + pad, key, rv);
  42         memset(key, 0, pad);
  43     }
  44     return rv + pad;
  45 }
  46
  47 static DH_METHOD dh_ossl = {
  48     "OpenSSL DH Method",
  49     generate_key,
  50     compute_key,
  51     dh_bn_mod_exp,
  52     dh_init,
  53     dh_finish,
  54     DH_FLAG_FIPS_METHOD,
  55     NULL,
  56     NULL
  57 };
  58
  59 static const DH_METHOD *default_DH_method = &dh_ossl;
  60
  61 const DH_METHOD *DH_OpenSSL(void)
  62 {
  63     return &dh_ossl;
  64 }
  65
  66 void DH_set_default_method(const DH_METHOD *meth)
  67 {
  68     default_DH_method = meth;
  69 }
  70
  71 const DH_METHOD *DH_get_default_method(void)
  72 {
  73     return default_DH_method;
  74 }
  75
  76 static int generate_key(DH *dh)
  77 {
  78     int ok = 0;
  79     int generate_new_key = 0;
  80     unsigned l;
  81     BN_CTX *ctx = NULL;
  82     BN_MONT_CTX *mont = NULL;
  83     BIGNUM *pub_key = NULL, *priv_key = NULL;
  84
  85     if (BN_num_bits(dh->p) > OPENSSL_DH_MAX_MODULUS_BITS) {
  86         DHerr(DH_F_GENERATE_KEY, DH_R_MODULUS_TOO_LARGE);
  87         return 0;
  88     }
  89
  90     if (BN_num_bits(dh->p) < DH_MIN_MODULUS_BITS) {
  91         DHerr(DH_F_GENERATE_KEY, DH_R_MODULUS_TOO_SMALL);
  92         return 0;
  93     }
  94
  95     ctx = BN_CTX_new();
  96     if (ctx == NULL)
  97         goto err;
  98
  99     if (dh->priv_key == NULL) {
 100         priv_key = BN_secure_new();
 101         if (priv_key == NULL)
 102             goto err;
 103         generate_new_key = 1;
 104     } else
 105         priv_key = dh->priv_key;
 106
 107     if (dh->pub_key == NULL) {
 108         pub_key = BN_new();
 109         if (pub_key == NULL)
 110             goto err;
 111     } else
 112         pub_key = dh->pub_key;
 113
 114     if (dh->flags & DH_FLAG_CACHE_MONT_P) {
 115         mont = BN_MONT_CTX_set_locked(&dh->method_mont_p,
 116                                       dh->lock, dh->p, ctx);
 117         if (!mont)
 118             goto err;
 119     }
 120
 121     if (generate_new_key) {
 122         if (dh->q) {
 123             do {
 124                 if (!BN_priv_rand_range(priv_key, dh->q))
 125                     goto err;
 126             }
 127             while (BN_is_zero(priv_key) || BN_is_one(priv_key));
 128         } else {
 129             /* secret exponent length */
 130             l = dh->length ? dh->length : BN_num_bits(dh->p) - 1;
 131             if (!BN_priv_rand(priv_key, l, BN_RAND_TOP_ONE, BN_RAND_BOTTOM_ANY))
 132                 goto err;
 133             /*
 134              * We handle just one known case where g is a quadratic non-residue:
 135              * for g = 2: p % 8 == 3
 136              */
 137             if (BN_is_word(dh->g, DH_GENERATOR_2) && !BN_is_bit_set(dh->p, 2)) {
 138                 /* clear bit 0, since it won't be a secret anyway */
 139                 if (!BN_clear_bit(priv_key, 0))
 140                     goto err;
 141             }
 142         }
 143     }
 144
 145     {
 146         BIGNUM *prk = BN_new();
 147
 148         if (prk == NULL)
 149             goto err;
 150         BN_with_flags(prk, priv_key, BN_FLG_CONSTTIME);
 151
 152         if (!dh->meth->bn_mod_exp(dh, pub_key, dh->g, prk, dh->p, ctx, mont)) {
 153             BN_clear_free(prk);
 154             goto err;
 155         }
 156         /* We MUST free prk before any further use of priv_key */
 157         BN_clear_free(prk);
 158     }
 159
 160     dh->pub_key = pub_key;
 161     dh->priv_key = priv_key;
 162     dh->dirty_cnt++;
 163     ok = 1;
 164  err:
 165     if (ok != 1)
 166         DHerr(DH_F_GENERATE_KEY, ERR_R_BN_LIB);
 167
 168     if (pub_key != dh->pub_key)
 169         BN_free(pub_key);
 170     if (priv_key != dh->priv_key)
 171         BN_free(priv_key);
 172     BN_CTX_free(ctx);
 173     return ok;
 174 }
 175
 176 static int compute_key(unsigned char *key, const BIGNUM *pub_key, DH *dh)
 177 {
 178     BN_CTX *ctx = NULL;
 179     BN_MONT_CTX *mont = NULL;
 180     BIGNUM *tmp;
 181     int ret = -1;
 182     int check_result;
 183
 184     if (BN_num_bits(dh->p) > OPENSSL_DH_MAX_MODULUS_BITS) {
 185         DHerr(DH_F_COMPUTE_KEY, DH_R_MODULUS_TOO_LARGE);
 186         goto err;
 187     }
 188
 189     if (BN_num_bits(dh->p) < DH_MIN_MODULUS_BITS) {
 190         DHerr(DH_F_COMPUTE_KEY, DH_R_MODULUS_TOO_SMALL);
 191         return 0;
 192     }
 193
 194     ctx = BN_CTX_new();
 195     if (ctx == NULL)
 196         goto err;
 197     BN_CTX_start(ctx);
 198     tmp = BN_CTX_get(ctx);
 199     if (tmp == NULL)
 200         goto err;
 201
 202     if (dh->priv_key == NULL) {
 203         DHerr(DH_F_COMPUTE_KEY, DH_R_NO_PRIVATE_VALUE);
 204         goto err;
 205     }
 206
 207     if (dh->flags & DH_FLAG_CACHE_MONT_P) {
 208         mont = BN_MONT_CTX_set_locked(&dh->method_mont_p,
 209                                       dh->lock, dh->p, ctx);
 210         BN_set_flags(dh->priv_key, BN_FLG_CONSTTIME);
 211         if (!mont)
 212             goto err;
 213     }
 214
 215     if (!DH_check_pub_key(dh, pub_key, &check_result) || check_result) {
 216         DHerr(DH_F_COMPUTE_KEY, DH_R_INVALID_PUBKEY);
 217         goto err;
 218     }
 219
 220     if (!dh->
 221         meth->bn_mod_exp(dh, tmp, pub_key, dh->priv_key, dh->p, ctx, mont)) {
 222         DHerr(DH_F_COMPUTE_KEY, ERR_R_BN_LIB);
 223         goto err;
 224     }
 225
 226     ret = BN_bn2bin(tmp, key);
 227  err:
 228     BN_CTX_end(ctx);
 229     BN_CTX_free(ctx);
 230     return ret;
 231 }
 232
 233 static int dh_bn_mod_exp(const DH *dh, BIGNUM *r,
 234                          const BIGNUM *a, const BIGNUM *p,
 235                          const BIGNUM *m, BN_CTX *ctx, BN_MONT_CTX *m_ctx)
 236 {
 237     return BN_mod_exp_mont(r, a, p, m, ctx, m_ctx);
 238 }
 239
 240 static int dh_init(DH *dh)
 241 {
 242     dh->flags |= DH_FLAG_CACHE_MONT_P;
 243     return 1;
 244 }
 245
 246 static int dh_finish(DH *dh)
 247 {
 248     BN_MONT_CTX_free(dh->method_mont_p);
 249     return 1;
 250 }
 251
 252 int dh_buf2key(DH *dh, const unsigned char *buf, size_t len)
 253 {
 254     int err_reason = DH_R_BN_ERROR;
 255     BIGNUM *pubkey = NULL;
 256     const BIGNUM *p;
 257     size_t p_size;
 258
 259     if ((pubkey = BN_bin2bn(buf, len, NULL)) == NULL)
 260         goto err;
 261     DH_get0_pqg(dh, &p, NULL, NULL);
 262     if (p == NULL || (p_size = BN_num_bytes(p)) == 0) {
 263         err_reason = DH_R_NO_PARAMETERS_SET;
 264         goto err;
 265     }
 266     /*
 267      * As per Section 4.2.8.1 of RFC 8446 fail if DHE's
 268      * public key is of size not equal to size of p
 269      */
 270     if (BN_is_zero(pubkey) || p_size != len) {
 271         err_reason = DH_R_INVALID_PUBKEY;
 272         goto err;
 273     }
 274     if (DH_set0_key(dh, pubkey, NULL) != 1)
 275         goto err;
 276     return 1;
 277 err:
 278     DHerr(DH_F_DH_BUF2KEY, err_reason);
 279     BN_free(pubkey);
 280     return 0;
 281 }
 282
 283 size_t dh_key2buf(const DH *dh, unsigned char **pbuf_out)
 284 {
 285     const BIGNUM *pubkey;
 286     unsigned char *pbuf;
 287     const BIGNUM *p;
 288     int p_size;
 289
 290     DH_get0_pqg(dh, &p, NULL, NULL);
 291     DH_get0_key(dh, &pubkey, NULL);
 292     if (p == NULL || pubkey == NULL
 293             || (p_size = BN_num_bytes(p)) == 0
 294             || BN_num_bytes(pubkey) == 0) {
 295         DHerr(DH_F_DH_KEY2BUF, DH_R_INVALID_PUBKEY);
 296         return 0;
 297     }
 298     if ((pbuf = OPENSSL_malloc(p_size)) == NULL) {
 299         DHerr(DH_F_DH_KEY2BUF, ERR_R_MALLOC_FAILURE);
 300         return 0;
 301     }
 302     /*
 303      * As per Section 4.2.8.1 of RFC 8446 left pad public
 304      * key with zeros to the size of p
 305      */
 306     if (BN_bn2binpad(pubkey, pbuf, p_size) < 0) {
 307         OPENSSL_free(pbuf);
 308         DHerr(DH_F_DH_KEY2BUF, DH_R_BN_ERROR);
 309         return 0;
 310     }
 311     *pbuf_out = pbuf;
 312     return p_size;
 313 }