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      1 /* Copyright (c) 2016, Google Inc.
      2  *
      3  * Permission to use, copy, modify, and/or distribute this software for any
      4  * purpose with or without fee is hereby granted, provided that the above
      5  * copyright notice and this permission notice appear in all copies.
      6  *
      7  * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
      8  * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
      9  * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
     10  * SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
     11  * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION
     12  * OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
     13  * CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. */
     14 
     15 #include <openssl/ssl.h>
     16 
     17 #include <assert.h>
     18 #include <string.h>
     19 
     20 #include <utility>
     21 
     22 #include <openssl/aead.h>
     23 #include <openssl/bytestring.h>
     24 #include <openssl/digest.h>
     25 #include <openssl/hkdf.h>
     26 #include <openssl/hmac.h>
     27 #include <openssl/mem.h>
     28 
     29 #include "../crypto/internal.h"
     30 #include "internal.h"
     31 
     32 
     33 namespace bssl {
     34 
     35 static int init_key_schedule(SSL_HANDSHAKE *hs, uint16_t version,
     36                              const SSL_CIPHER *cipher) {
     37   if (!hs->transcript.InitHash(version, cipher)) {
     38     return 0;
     39   }
     40 
     41   hs->hash_len = hs->transcript.DigestLen();
     42 
     43   // Initialize the secret to the zero key.
     44   OPENSSL_memset(hs->secret, 0, hs->hash_len);
     45 
     46   return 1;
     47 }
     48 
     49 int tls13_init_key_schedule(SSL_HANDSHAKE *hs, const uint8_t *psk,
     50                             size_t psk_len) {
     51   if (!init_key_schedule(hs, ssl_protocol_version(hs->ssl), hs->new_cipher)) {
     52     return 0;
     53   }
     54 
     55   hs->transcript.FreeBuffer();
     56   return HKDF_extract(hs->secret, &hs->hash_len, hs->transcript.Digest(), psk,
     57                       psk_len, hs->secret, hs->hash_len);
     58 }
     59 
     60 int tls13_init_early_key_schedule(SSL_HANDSHAKE *hs, const uint8_t *psk,
     61                                   size_t psk_len) {
     62   SSL *const ssl = hs->ssl;
     63   return init_key_schedule(hs, ssl_session_protocol_version(ssl->session),
     64                            ssl->session->cipher) &&
     65          HKDF_extract(hs->secret, &hs->hash_len, hs->transcript.Digest(), psk,
     66                       psk_len, hs->secret, hs->hash_len);
     67 }
     68 
     69 static int hkdf_expand_label(uint8_t *out, const EVP_MD *digest,
     70                              const uint8_t *secret, size_t secret_len,
     71                              const char *label, size_t label_len,
     72                              const uint8_t *hash, size_t hash_len, size_t len) {
     73   static const char kTLS13LabelVersion[] = "tls13 ";
     74 
     75   ScopedCBB cbb;
     76   CBB child;
     77   uint8_t *hkdf_label;
     78   size_t hkdf_label_len;
     79   if (!CBB_init(cbb.get(), 2 + 1 + strlen(kTLS13LabelVersion) + label_len + 1 +
     80                                hash_len) ||
     81       !CBB_add_u16(cbb.get(), len) ||
     82       !CBB_add_u8_length_prefixed(cbb.get(), &child) ||
     83       !CBB_add_bytes(&child, (const uint8_t *)kTLS13LabelVersion,
     84                      strlen(kTLS13LabelVersion)) ||
     85       !CBB_add_bytes(&child, (const uint8_t *)label, label_len) ||
     86       !CBB_add_u8_length_prefixed(cbb.get(), &child) ||
     87       !CBB_add_bytes(&child, hash, hash_len) ||
     88       !CBB_finish(cbb.get(), &hkdf_label, &hkdf_label_len)) {
     89     return 0;
     90   }
     91 
     92   int ret = HKDF_expand(out, len, digest, secret, secret_len, hkdf_label,
     93                         hkdf_label_len);
     94   OPENSSL_free(hkdf_label);
     95   return ret;
     96 }
     97 
     98 static const char kTLS13LabelDerived[] = "derived";
     99 
    100 int tls13_advance_key_schedule(SSL_HANDSHAKE *hs, const uint8_t *in,
    101                                size_t len) {
    102   uint8_t derive_context[EVP_MAX_MD_SIZE];
    103   unsigned derive_context_len;
    104   if (!EVP_Digest(nullptr, 0, derive_context, &derive_context_len,
    105                   hs->transcript.Digest(), nullptr)) {
    106     return 0;
    107   }
    108 
    109   if (!hkdf_expand_label(hs->secret, hs->transcript.Digest(), hs->secret,
    110                          hs->hash_len, kTLS13LabelDerived,
    111                          strlen(kTLS13LabelDerived), derive_context,
    112                          derive_context_len, hs->hash_len)) {
    113     return 0;
    114   }
    115 
    116   return HKDF_extract(hs->secret, &hs->hash_len, hs->transcript.Digest(), in,
    117                       len, hs->secret, hs->hash_len);
    118 }
    119 
    120 // derive_secret derives a secret of length |len| and writes the result in |out|
    121 // with the given label and the current base secret and most recently-saved
    122 // handshake context. It returns one on success and zero on error.
    123 static int derive_secret(SSL_HANDSHAKE *hs, uint8_t *out, size_t len,
    124                          const char *label, size_t label_len) {
    125   uint8_t context_hash[EVP_MAX_MD_SIZE];
    126   size_t context_hash_len;
    127   if (!hs->transcript.GetHash(context_hash, &context_hash_len)) {
    128     return 0;
    129   }
    130 
    131   return hkdf_expand_label(out, hs->transcript.Digest(), hs->secret,
    132                            hs->hash_len, label, label_len, context_hash,
    133                            context_hash_len, len);
    134 }
    135 
    136 int tls13_set_traffic_key(SSL *ssl, enum evp_aead_direction_t direction,
    137                           const uint8_t *traffic_secret,
    138                           size_t traffic_secret_len) {
    139   const SSL_SESSION *session = SSL_get_session(ssl);
    140   uint16_t version = ssl_session_protocol_version(session);
    141 
    142   if (traffic_secret_len > 0xff) {
    143     OPENSSL_PUT_ERROR(SSL, ERR_R_OVERFLOW);
    144     return 0;
    145   }
    146 
    147   // Look up cipher suite properties.
    148   const EVP_AEAD *aead;
    149   size_t discard;
    150   if (!ssl_cipher_get_evp_aead(&aead, &discard, &discard, session->cipher,
    151                                version, SSL_is_dtls(ssl))) {
    152     return 0;
    153   }
    154 
    155   const EVP_MD *digest = ssl_session_get_digest(session);
    156 
    157   // Derive the key.
    158   size_t key_len = EVP_AEAD_key_length(aead);
    159   uint8_t key[EVP_AEAD_MAX_KEY_LENGTH];
    160   if (!hkdf_expand_label(key, digest, traffic_secret, traffic_secret_len, "key",
    161                          3, NULL, 0, key_len)) {
    162     return 0;
    163   }
    164 
    165   // Derive the IV.
    166   size_t iv_len = EVP_AEAD_nonce_length(aead);
    167   uint8_t iv[EVP_AEAD_MAX_NONCE_LENGTH];
    168   if (!hkdf_expand_label(iv, digest, traffic_secret, traffic_secret_len, "iv",
    169                          2, NULL, 0, iv_len)) {
    170     return 0;
    171   }
    172 
    173   UniquePtr<SSLAEADContext> traffic_aead =
    174       SSLAEADContext::Create(direction, session->ssl_version, SSL_is_dtls(ssl),
    175                              session->cipher, MakeConstSpan(key, key_len),
    176                              Span<const uint8_t>(), MakeConstSpan(iv, iv_len));
    177   if (!traffic_aead) {
    178     return 0;
    179   }
    180 
    181   if (direction == evp_aead_open) {
    182     if (!ssl->method->set_read_state(ssl, std::move(traffic_aead))) {
    183       return 0;
    184     }
    185   } else {
    186     if (!ssl->method->set_write_state(ssl, std::move(traffic_aead))) {
    187       return 0;
    188     }
    189   }
    190 
    191   // Save the traffic secret.
    192   if (direction == evp_aead_open) {
    193     OPENSSL_memmove(ssl->s3->read_traffic_secret, traffic_secret,
    194                     traffic_secret_len);
    195     ssl->s3->read_traffic_secret_len = traffic_secret_len;
    196   } else {
    197     OPENSSL_memmove(ssl->s3->write_traffic_secret, traffic_secret,
    198                     traffic_secret_len);
    199     ssl->s3->write_traffic_secret_len = traffic_secret_len;
    200   }
    201 
    202   return 1;
    203 }
    204 
    205 
    206 static const char kTLS13LabelExporter[] = "exp master";
    207 static const char kTLS13LabelEarlyExporter[] = "e exp master";
    208 
    209 static const char kTLS13LabelClientEarlyTraffic[] = "c e traffic";
    210 static const char kTLS13LabelClientHandshakeTraffic[] = "c hs traffic";
    211 static const char kTLS13LabelServerHandshakeTraffic[] = "s hs traffic";
    212 static const char kTLS13LabelClientApplicationTraffic[] = "c ap traffic";
    213 static const char kTLS13LabelServerApplicationTraffic[] = "s ap traffic";
    214 
    215 int tls13_derive_early_secrets(SSL_HANDSHAKE *hs) {
    216   SSL *const ssl = hs->ssl;
    217   if (!derive_secret(hs, hs->early_traffic_secret, hs->hash_len,
    218                      kTLS13LabelClientEarlyTraffic,
    219                      strlen(kTLS13LabelClientEarlyTraffic)) ||
    220       !ssl_log_secret(ssl, "CLIENT_EARLY_TRAFFIC_SECRET",
    221                       hs->early_traffic_secret, hs->hash_len) ||
    222       !derive_secret(hs, ssl->s3->early_exporter_secret, hs->hash_len,
    223                      kTLS13LabelEarlyExporter,
    224                      strlen(kTLS13LabelEarlyExporter))) {
    225     return 0;
    226   }
    227   ssl->s3->early_exporter_secret_len = hs->hash_len;
    228   return 1;
    229 }
    230 
    231 int tls13_derive_handshake_secrets(SSL_HANDSHAKE *hs) {
    232   SSL *const ssl = hs->ssl;
    233   return derive_secret(hs, hs->client_handshake_secret, hs->hash_len,
    234                        kTLS13LabelClientHandshakeTraffic,
    235                        strlen(kTLS13LabelClientHandshakeTraffic)) &&
    236          ssl_log_secret(ssl, "CLIENT_HANDSHAKE_TRAFFIC_SECRET",
    237                         hs->client_handshake_secret, hs->hash_len) &&
    238          derive_secret(hs, hs->server_handshake_secret, hs->hash_len,
    239                        kTLS13LabelServerHandshakeTraffic,
    240                        strlen(kTLS13LabelServerHandshakeTraffic)) &&
    241          ssl_log_secret(ssl, "SERVER_HANDSHAKE_TRAFFIC_SECRET",
    242                         hs->server_handshake_secret, hs->hash_len);
    243 }
    244 
    245 int tls13_derive_application_secrets(SSL_HANDSHAKE *hs) {
    246   SSL *const ssl = hs->ssl;
    247   ssl->s3->exporter_secret_len = hs->hash_len;
    248   return derive_secret(hs, hs->client_traffic_secret_0, hs->hash_len,
    249                        kTLS13LabelClientApplicationTraffic,
    250                        strlen(kTLS13LabelClientApplicationTraffic)) &&
    251          ssl_log_secret(ssl, "CLIENT_TRAFFIC_SECRET_0",
    252                         hs->client_traffic_secret_0, hs->hash_len) &&
    253          derive_secret(hs, hs->server_traffic_secret_0, hs->hash_len,
    254                        kTLS13LabelServerApplicationTraffic,
    255                        strlen(kTLS13LabelServerApplicationTraffic)) &&
    256          ssl_log_secret(ssl, "SERVER_TRAFFIC_SECRET_0",
    257                         hs->server_traffic_secret_0, hs->hash_len) &&
    258          derive_secret(hs, ssl->s3->exporter_secret, hs->hash_len,
    259                        kTLS13LabelExporter, strlen(kTLS13LabelExporter)) &&
    260          ssl_log_secret(ssl, "EXPORTER_SECRET", ssl->s3->exporter_secret,
    261                         hs->hash_len);
    262 }
    263 
    264 static const char kTLS13LabelApplicationTraffic[] = "traffic upd";
    265 
    266 int tls13_rotate_traffic_key(SSL *ssl, enum evp_aead_direction_t direction) {
    267   uint8_t *secret;
    268   size_t secret_len;
    269   if (direction == evp_aead_open) {
    270     secret = ssl->s3->read_traffic_secret;
    271     secret_len = ssl->s3->read_traffic_secret_len;
    272   } else {
    273     secret = ssl->s3->write_traffic_secret;
    274     secret_len = ssl->s3->write_traffic_secret_len;
    275   }
    276 
    277   const EVP_MD *digest = ssl_session_get_digest(SSL_get_session(ssl));
    278   if (!hkdf_expand_label(
    279           secret, digest, secret, secret_len, kTLS13LabelApplicationTraffic,
    280           strlen(kTLS13LabelApplicationTraffic), NULL, 0, secret_len)) {
    281     return 0;
    282   }
    283 
    284   return tls13_set_traffic_key(ssl, direction, secret, secret_len);
    285 }
    286 
    287 static const char kTLS13LabelResumption[] = "res master";
    288 
    289 int tls13_derive_resumption_secret(SSL_HANDSHAKE *hs) {
    290   if (hs->hash_len > SSL_MAX_MASTER_KEY_LENGTH) {
    291     OPENSSL_PUT_ERROR(SSL, ERR_R_INTERNAL_ERROR);
    292     return 0;
    293   }
    294   hs->new_session->master_key_length = hs->hash_len;
    295   return derive_secret(hs, hs->new_session->master_key,
    296                        hs->new_session->master_key_length,
    297                        kTLS13LabelResumption, strlen(kTLS13LabelResumption));
    298 }
    299 
    300 static const char kTLS13LabelFinished[] = "finished";
    301 
    302 // tls13_verify_data sets |out| to be the HMAC of |context| using a derived
    303 // Finished key for both Finished messages and the PSK binder.
    304 static int tls13_verify_data(const EVP_MD *digest, uint16_t version,
    305                              uint8_t *out, size_t *out_len,
    306                              const uint8_t *secret, size_t hash_len,
    307                              uint8_t *context, size_t context_len) {
    308   uint8_t key[EVP_MAX_MD_SIZE];
    309   unsigned len;
    310   if (!hkdf_expand_label(key, digest, secret, hash_len, kTLS13LabelFinished,
    311                          strlen(kTLS13LabelFinished), NULL, 0, hash_len) ||
    312       HMAC(digest, key, hash_len, context, context_len, out, &len) == NULL) {
    313     return 0;
    314   }
    315   *out_len = len;
    316   return 1;
    317 }
    318 
    319 int tls13_finished_mac(SSL_HANDSHAKE *hs, uint8_t *out, size_t *out_len,
    320                        int is_server) {
    321   const uint8_t *traffic_secret;
    322   if (is_server) {
    323     traffic_secret = hs->server_handshake_secret;
    324   } else {
    325     traffic_secret = hs->client_handshake_secret;
    326   }
    327 
    328   uint8_t context_hash[EVP_MAX_MD_SIZE];
    329   size_t context_hash_len;
    330   if (!hs->transcript.GetHash(context_hash, &context_hash_len) ||
    331       !tls13_verify_data(hs->transcript.Digest(), hs->ssl->version, out,
    332                          out_len, traffic_secret, hs->hash_len, context_hash,
    333                          context_hash_len)) {
    334     return 0;
    335   }
    336   return 1;
    337 }
    338 
    339 static const char kTLS13LabelResumptionPSK[] = "resumption";
    340 
    341 bool tls13_derive_session_psk(SSL_SESSION *session, Span<const uint8_t> nonce) {
    342   const EVP_MD *digest = ssl_session_get_digest(session);
    343   return hkdf_expand_label(session->master_key, digest, session->master_key,
    344                            session->master_key_length, kTLS13LabelResumptionPSK,
    345                            strlen(kTLS13LabelResumptionPSK), nonce.data(),
    346                            nonce.size(), session->master_key_length);
    347 }
    348 
    349 static const char kTLS13LabelExportKeying[] = "exporter";
    350 
    351 int tls13_export_keying_material(SSL *ssl, Span<uint8_t> out,
    352                                  Span<const uint8_t> secret,
    353                                  Span<const char> label,
    354                                  Span<const uint8_t> context) {
    355   if (secret.empty()) {
    356     assert(0);
    357     OPENSSL_PUT_ERROR(SSL, ERR_R_INTERNAL_ERROR);
    358     return 0;
    359   }
    360 
    361   const EVP_MD *digest = ssl_session_get_digest(SSL_get_session(ssl));
    362 
    363   uint8_t hash[EVP_MAX_MD_SIZE];
    364   uint8_t export_context[EVP_MAX_MD_SIZE];
    365   uint8_t derived_secret[EVP_MAX_MD_SIZE];
    366   unsigned hash_len;
    367   unsigned export_context_len;
    368   unsigned derived_secret_len = EVP_MD_size(digest);
    369   return EVP_Digest(context.data(), context.size(), hash, &hash_len, digest,
    370                     nullptr) &&
    371          EVP_Digest(nullptr, 0, export_context, &export_context_len, digest,
    372                     nullptr) &&
    373          hkdf_expand_label(derived_secret, digest, secret.data(), secret.size(),
    374                            label.data(), label.size(), export_context,
    375                            export_context_len, derived_secret_len) &&
    376          hkdf_expand_label(out.data(), digest, derived_secret,
    377                            derived_secret_len, kTLS13LabelExportKeying,
    378                            strlen(kTLS13LabelExportKeying), hash, hash_len,
    379                            out.size());
    380 }
    381 
    382 static const char kTLS13LabelPSKBinder[] = "res binder";
    383 
    384 static int tls13_psk_binder(uint8_t *out, uint16_t version,
    385                             const EVP_MD *digest, uint8_t *psk, size_t psk_len,
    386                             uint8_t *context, size_t context_len,
    387                             size_t hash_len) {
    388   uint8_t binder_context[EVP_MAX_MD_SIZE];
    389   unsigned binder_context_len;
    390   if (!EVP_Digest(NULL, 0, binder_context, &binder_context_len, digest, NULL)) {
    391     return 0;
    392   }
    393 
    394   uint8_t early_secret[EVP_MAX_MD_SIZE] = {0};
    395   size_t early_secret_len;
    396   if (!HKDF_extract(early_secret, &early_secret_len, digest, psk, hash_len,
    397                     NULL, 0)) {
    398     return 0;
    399   }
    400 
    401   uint8_t binder_key[EVP_MAX_MD_SIZE] = {0};
    402   size_t len;
    403   if (!hkdf_expand_label(binder_key, digest, early_secret, hash_len,
    404                          kTLS13LabelPSKBinder, strlen(kTLS13LabelPSKBinder),
    405                          binder_context, binder_context_len, hash_len) ||
    406       !tls13_verify_data(digest, version, out, &len, binder_key, hash_len,
    407                          context, context_len)) {
    408     return 0;
    409   }
    410 
    411   return 1;
    412 }
    413 
    414 int tls13_write_psk_binder(SSL_HANDSHAKE *hs, uint8_t *msg, size_t len) {
    415   SSL *const ssl = hs->ssl;
    416   const EVP_MD *digest = ssl_session_get_digest(ssl->session);
    417   size_t hash_len = EVP_MD_size(digest);
    418 
    419   if (len < hash_len + 3) {
    420     OPENSSL_PUT_ERROR(SSL, ERR_R_INTERNAL_ERROR);
    421     return 0;
    422   }
    423 
    424   ScopedEVP_MD_CTX ctx;
    425   uint8_t context[EVP_MAX_MD_SIZE];
    426   unsigned context_len;
    427 
    428   if (!EVP_DigestInit_ex(ctx.get(), digest, NULL) ||
    429       !EVP_DigestUpdate(ctx.get(), hs->transcript.buffer().data(),
    430                         hs->transcript.buffer().size()) ||
    431       !EVP_DigestUpdate(ctx.get(), msg, len - hash_len - 3) ||
    432       !EVP_DigestFinal_ex(ctx.get(), context, &context_len)) {
    433     return 0;
    434   }
    435 
    436   uint8_t verify_data[EVP_MAX_MD_SIZE] = {0};
    437   if (!tls13_psk_binder(verify_data, ssl->session->ssl_version, digest,
    438                         ssl->session->master_key,
    439                         ssl->session->master_key_length, context, context_len,
    440                         hash_len)) {
    441     return 0;
    442   }
    443 
    444   OPENSSL_memcpy(msg + len - hash_len, verify_data, hash_len);
    445   return 1;
    446 }
    447 
    448 int tls13_verify_psk_binder(SSL_HANDSHAKE *hs, SSL_SESSION *session,
    449                             const SSLMessage &msg, CBS *binders) {
    450   size_t hash_len = hs->transcript.DigestLen();
    451 
    452   // The message must be large enough to exclude the binders.
    453   if (CBS_len(&msg.raw) < CBS_len(binders) + 2) {
    454     OPENSSL_PUT_ERROR(SSL, ERR_R_INTERNAL_ERROR);
    455     return 0;
    456   }
    457 
    458   // Hash a ClientHello prefix up to the binders. This includes the header. For
    459   // now, this assumes we only ever verify PSK binders on initial
    460   // ClientHellos.
    461   uint8_t context[EVP_MAX_MD_SIZE];
    462   unsigned context_len;
    463   if (!EVP_Digest(CBS_data(&msg.raw), CBS_len(&msg.raw) - CBS_len(binders) - 2,
    464                   context, &context_len, hs->transcript.Digest(), NULL)) {
    465     return 0;
    466   }
    467 
    468   uint8_t verify_data[EVP_MAX_MD_SIZE] = {0};
    469   CBS binder;
    470   if (!tls13_psk_binder(verify_data, hs->ssl->version, hs->transcript.Digest(),
    471                         session->master_key, session->master_key_length,
    472                         context, context_len, hash_len) ||
    473       // We only consider the first PSK, so compare against the first binder.
    474       !CBS_get_u8_length_prefixed(binders, &binder)) {
    475     OPENSSL_PUT_ERROR(SSL, ERR_R_INTERNAL_ERROR);
    476     return 0;
    477   }
    478 
    479   int binder_ok =
    480       CBS_len(&binder) == hash_len &&
    481       CRYPTO_memcmp(CBS_data(&binder), verify_data, hash_len) == 0;
    482 #if defined(BORINGSSL_UNSAFE_FUZZER_MODE)
    483   binder_ok = 1;
    484 #endif
    485   if (!binder_ok) {
    486     OPENSSL_PUT_ERROR(SSL, SSL_R_DIGEST_CHECK_FAILED);
    487     return 0;
    488   }
    489 
    490   return 1;
    491 }
    492 
    493 }  // namespace bssl
    494