src/lib/crypt_ops/crypto_hkdf.c

   1 /* Copyright (c) 2001, Matej Pfajfar.
   2  * Copyright (c) 2001-2004, Roger Dingledine.
   3  * Copyright (c) 2004-2006, Roger Dingledine, Nick Mathewson.
   4  * Copyright (c) 2007-2019, The Tor Project, Inc. */
   5 /* See LICENSE for licensing information */
   6
   7 /**
   8  * \file crypto_hkdf.c
   9  * \brief Block of functions related with HKDF utilities and operations.
  10  **/
  11
  12 #include "lib/crypt_ops/crypto_hkdf.h"
  13 #include "lib/crypt_ops/crypto_util.h"
  14 #include "lib/crypt_ops/crypto_digest.h"
  15
  16 #include "lib/crypt_ops/crypto_openssl_mgt.h"
  17 #include "lib/intmath/cmp.h"
  18 #include "lib/log/util_bug.h"
  19
  20 #ifdef ENABLE_OPENSSL
  21 #include <openssl/opensslv.h>
  22
  23 #if defined(HAVE_ERR_LOAD_KDF_STRINGS)
  24 #include <openssl/kdf.h>
  25 #define HAVE_OPENSSL_HKDF 1
  26 #endif
  27 #endif
  28
  29 #include <string.h>
  30
  31 /** Given <b>key_in_len</b> bytes of negotiated randomness in <b>key_in</b>
  32  * ("K"), expand it into <b>key_out_len</b> bytes of negotiated key material in
  33  * <b>key_out</b> by taking the first <b>key_out_len</b> bytes of
  34  *    H(K | [00]) | H(K | [01]) | ....
  35  *
  36  * This is the key expansion algorithm used in the "TAP" circuit extension
  37  * mechanism; it shouldn't be used for new protocols.
  38  *
  39  * Return 0 on success, -1 on failure.
  40  */
  41 int
  42 crypto_expand_key_material_TAP(const uint8_t *key_in, size_t key_in_len,
  43                                uint8_t *key_out, size_t key_out_len)
  44 {
  45   int i, r = -1;
  46   uint8_t *cp, *tmp = tor_malloc(key_in_len+1);
  47   uint8_t digest[DIGEST_LEN];
  48
  49   /* If we try to get more than this amount of key data, we'll repeat blocks.*/
  50   tor_assert(key_out_len <= DIGEST_LEN*256);
  51
  52   memcpy(tmp, key_in, key_in_len);
  53   for (cp = key_out, i=0; cp < key_out+key_out_len;
  54        ++i, cp += DIGEST_LEN) {
  55     tmp[key_in_len] = i;
  56     if (crypto_digest((char*)digest, (const char *)tmp, key_in_len+1) < 0)
  57       goto exit;
  58     memcpy(cp, digest, MIN(DIGEST_LEN, key_out_len-(cp-key_out)));
  59   }
  60
  61   r = 0;
  62  exit:
  63   memwipe(tmp, 0, key_in_len+1);
  64   tor_free(tmp);
  65   memwipe(digest, 0, sizeof(digest));
  66   return r;
  67 }
  68
  69 #ifdef HAVE_OPENSSL_HKDF
  70 /**
  71  * Perform RFC5869 HKDF computation using OpenSSL (only to be called from
  72  * crypto_expand_key_material_rfc5869_sha256_openssl). Note that OpenSSL
  73  * requires input key to be nonempty and salt length to be equal or less
  74  * than 1024.
  75  */
  76 static int
  77 crypto_expand_key_material_rfc5869_sha256_openssl(
  78                                     const uint8_t *key_in, size_t key_in_len,
  79                                     const uint8_t *salt_in, size_t salt_in_len,
  80                                     const uint8_t *info_in, size_t info_in_len,
  81                                     uint8_t *key_out, size_t key_out_len)
  82 {
  83   int r;
  84   EVP_PKEY_CTX *evp_pkey_ctx = EVP_PKEY_CTX_new_id(EVP_PKEY_HKDF, NULL);
  85   tor_assert(evp_pkey_ctx);
  86   tor_assert(key_in_len != 0);
  87   tor_assert(salt_in_len <= 1024);
  88
  89   r = EVP_PKEY_derive_init(evp_pkey_ctx);
  90   tor_assert(r == 1);
  91
  92   r = EVP_PKEY_CTX_set_hkdf_md(evp_pkey_ctx, EVP_sha256());
  93   tor_assert(r == 1);
  94
  95   r = EVP_PKEY_CTX_set1_hkdf_salt(evp_pkey_ctx, salt_in, (int)salt_in_len);
  96   tor_assert(r == 1);
  97
  98   r = EVP_PKEY_CTX_set1_hkdf_key(evp_pkey_ctx, key_in, (int)key_in_len);
  99   tor_assert(r == 1);
 100
 101   r = EVP_PKEY_CTX_add1_hkdf_info(evp_pkey_ctx, info_in, (int)info_in_len);
 102   tor_assert(r == 1);
 103
 104   r = EVP_PKEY_derive(evp_pkey_ctx, key_out, &key_out_len);
 105   tor_assert(r == 1);
 106
 107   EVP_PKEY_CTX_free(evp_pkey_ctx);
 108   return 0;
 109 }
 110
 111 #else
 112
 113 /**
 114  * Perform RFC5869 HKDF computation using our own legacy implementation.
 115  * Only to be called from crypto_expand_key_material_rfc5869_sha256_openssl.
 116  */
 117 static int
 118 crypto_expand_key_material_rfc5869_sha256_legacy(
 119                                     const uint8_t *key_in, size_t key_in_len,
 120                                     const uint8_t *salt_in, size_t salt_in_len,
 121                                     const uint8_t *info_in, size_t info_in_len,
 122                                     uint8_t *key_out, size_t key_out_len)
 123 {
 124   uint8_t prk[DIGEST256_LEN];
 125   uint8_t tmp[DIGEST256_LEN + 128 + 1];
 126   uint8_t mac[DIGEST256_LEN];
 127   int i;
 128   uint8_t *outp;
 129   size_t tmp_len;
 130
 131   crypto_hmac_sha256((char*)prk,
 132                      (const char*)salt_in, salt_in_len,
 133                      (const char*)key_in, key_in_len);
 134
 135   /* If we try to get more than this amount of key data, we'll repeat blocks.*/
 136   tor_assert(key_out_len <= DIGEST256_LEN * 256);
 137   tor_assert(info_in_len <= 128);
 138   memset(tmp, 0, sizeof(tmp));
 139   outp = key_out;
 140   i = 1;
 141
 142   while (key_out_len) {
 143     size_t n;
 144     if (i > 1) {
 145       memcpy(tmp, mac, DIGEST256_LEN);
 146       memcpy(tmp+DIGEST256_LEN, info_in, info_in_len);
 147       tmp[DIGEST256_LEN+info_in_len] = i;
 148       tmp_len = DIGEST256_LEN + info_in_len + 1;
 149     } else {
 150       memcpy(tmp, info_in, info_in_len);
 151       tmp[info_in_len] = i;
 152       tmp_len = info_in_len + 1;
 153     }
 154     crypto_hmac_sha256((char*)mac,
 155                        (const char*)prk, DIGEST256_LEN,
 156                        (const char*)tmp, tmp_len);
 157     n = key_out_len < DIGEST256_LEN ? key_out_len : DIGEST256_LEN;
 158     memcpy(outp, mac, n);
 159     key_out_len -= n;
 160     outp += n;
 161     ++i;
 162   }
 163
 164   memwipe(tmp, 0, sizeof(tmp));
 165   memwipe(mac, 0, sizeof(mac));
 166   return 0;
 167 }
 168 #endif
 169
 170 /** Expand some secret key material according to RFC5869, using SHA256 as the
 171  * underlying hash.  The <b>key_in_len</b> bytes at <b>key_in</b> are the
 172  * secret key material; the <b>salt_in_len</b> bytes at <b>salt_in</b> and the
 173  * <b>info_in_len</b> bytes in <b>info_in_len</b> are the algorithm's "salt"
 174  * and "info" parameters respectively.  On success, write <b>key_out_len</b>
 175  * bytes to <b>key_out</b> and return 0.  Assert on failure.
 176  */
 177 int
 178 crypto_expand_key_material_rfc5869_sha256(
 179                                     const uint8_t *key_in, size_t key_in_len,
 180                                     const uint8_t *salt_in, size_t salt_in_len,
 181                                     const uint8_t *info_in, size_t info_in_len,
 182                                     uint8_t *key_out, size_t key_out_len)
 183 {
 184   tor_assert(key_in);
 185   tor_assert(key_in_len > 0);
 186
 187 #ifdef HAVE_OPENSSL_HKDF
 188   return crypto_expand_key_material_rfc5869_sha256_openssl(key_in,
 189                                              key_in_len, salt_in,
 190                                              salt_in_len, info_in,
 191                                              info_in_len,
 192                                              key_out, key_out_len);
 193 #else
 194   return crypto_expand_key_material_rfc5869_sha256_legacy(key_in,
 195                                                key_in_len, salt_in,
 196                                                salt_in_len, info_in,
 197                                                info_in_len,
 198                                                key_out, key_out_len);
 199 #endif
 200 }