media/cdm/json_web_key.cc

   1 // Copyright 2013 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #include "media/cdm/json_web_key.h"
   6
   7 #include "base/base64.h"
   8 #include "base/json/json_reader.h"
   9 #include "base/json/json_string_value_serializer.h"
  10 #include "base/json/string_escape.h"
  11 #include "base/logging.h"
  12 #include "base/memory/scoped_ptr.h"
  13 #include "base/strings/string_number_conversions.h"
  14 #include "base/strings/string_util.h"
  15 #include "base/values.h"
  16
  17 namespace media {
  18
  19 const char kKeysTag[] = "keys";
  20 const char kKeyTypeTag[] = "kty";
  21 const char kKeyTypeOct[] = "oct";  // Octet sequence.
  22 const char kKeyTag[] = "k";
  23 const char kKeyIdTag[] = "kid";
  24 const char kKeyIdsTag[] = "kids";
  25 const char kBase64Padding = '=';
  26 const char kBase64Plus[] = "+";
  27 const char kBase64UrlPlusReplacement[] = "-";
  28 const char kBase64Slash[] = "/";
  29 const char kBase64UrlSlashReplacement[] = "_";
  30 const char kBase64UrlInvalid[] = "+/=";
  31 const char kTypeTag[] = "type";
  32 const char kTemporarySession[] = "temporary";
  33 const char kPersistentLicenseSession[] = "persistent-license";
  34 const char kPersistentReleaseMessageSession[] = "persistent-release-message";
  35
  36 // Encodes |input| into a base64url string without padding.
  37 static std::string EncodeBase64Url(const uint8* input, int input_length) {
  38   std::string encoded_text;
  39   base::Base64Encode(
  40       std::string(reinterpret_cast<const char*>(input), input_length),
  41       &encoded_text);
  42
  43   // Remove any padding characters added by Base64Encode().
  44   size_t found = encoded_text.find_last_not_of(kBase64Padding);
  45   if (found != std::string::npos)
  46     encoded_text.erase(found + 1);
  47
  48   // base64url encoding means the characters '-' and '_' must be used
  49   // instead of '+' and '/', respectively.
  50   base::ReplaceChars(encoded_text, kBase64Plus, kBase64UrlPlusReplacement,
  51                      &encoded_text);
  52   base::ReplaceChars(encoded_text, kBase64Slash, kBase64UrlSlashReplacement,
  53                      &encoded_text);
  54
  55   return encoded_text;
  56 }
  57
  58 // Decodes a base64url string. Returns empty string on error.
  59 static std::string DecodeBase64Url(const std::string& encoded_text) {
  60   // EME spec doesn't allow '+', '/', or padding characters.
  61   if (encoded_text.find_first_of(kBase64UrlInvalid) != std::string::npos) {
  62     DVLOG(1) << "Invalid base64url format: " << encoded_text;
  63     return std::string();
  64   }
  65
  66   // Since base::Base64Decode() requires padding characters, add them so length
  67   // of |encoded_text| is exactly a multiple of 4.
  68   size_t num_last_grouping_chars = encoded_text.length() % 4;
  69   std::string modified_text = encoded_text;
  70   if (num_last_grouping_chars > 0)
  71     modified_text.append(4 - num_last_grouping_chars, kBase64Padding);
  72
  73   // base64url encoding means the characters '-' and '_' must be used
  74   // instead of '+' and '/', respectively, so replace them before calling
  75   // base::Base64Decode().
  76   base::ReplaceChars(modified_text, kBase64UrlPlusReplacement, kBase64Plus,
  77                      &modified_text);
  78   base::ReplaceChars(modified_text, kBase64UrlSlashReplacement, kBase64Slash,
  79                      &modified_text);
  80
  81   std::string decoded_text;
  82   if (!base::Base64Decode(modified_text, &decoded_text)) {
  83     DVLOG(1) << "Base64 decoding failed on: " << modified_text;
  84     return std::string();
  85   }
  86
  87   return decoded_text;
  88 }
  89
  90 static std::string ShortenTo64Characters(const std::string& input) {
  91   // Convert |input| into a string with escaped characters replacing any
  92   // non-ASCII characters. Limiting |input| to the first 65 characters so
  93   // we don't waste time converting a potentially long string and then
  94   // throwing away the excess.
  95   std::string escaped_str =
  96       base::EscapeBytesAsInvalidJSONString(input.substr(0, 65), false);
  97   if (escaped_str.length() <= 64u)
  98     return escaped_str;
  99
 100   // This may end up truncating an escaped character, but the first part of
 101   // the string should provide enough information.
 102   return escaped_str.substr(0, 61).append("...");
 103 }
 104
 105 std::string GenerateJWKSet(const uint8* key, int key_length,
 106                            const uint8* key_id, int key_id_length) {
 107   // Both |key| and |key_id| need to be base64 encoded strings in the JWK.
 108   std::string key_base64 = EncodeBase64Url(key, key_length);
 109   std::string key_id_base64 = EncodeBase64Url(key_id, key_id_length);
 110
 111   // Create the JWK, and wrap it into a JWK Set.
 112   scoped_ptr<base::DictionaryValue> jwk(new base::DictionaryValue());
 113   jwk->SetString(kKeyTypeTag, kKeyTypeOct);
 114   jwk->SetString(kKeyTag, key_base64);
 115   jwk->SetString(kKeyIdTag, key_id_base64);
 116   scoped_ptr<base::ListValue> list(new base::ListValue());
 117   list->Append(jwk.release());
 118   base::DictionaryValue jwk_set;
 119   jwk_set.Set(kKeysTag, list.release());
 120
 121   // Finally serialize |jwk_set| into a string and return it.
 122   std::string serialized_jwk;
 123   JSONStringValueSerializer serializer(&serialized_jwk);
 124   serializer.Serialize(jwk_set);
 125   return serialized_jwk;
 126 }
 127
 128 // Processes a JSON Web Key to extract the key id and key value. Sets |jwk_key|
 129 // to the id/value pair and returns true on success.
 130 static bool ConvertJwkToKeyPair(const base::DictionaryValue& jwk,
 131                                 KeyIdAndKeyPair* jwk_key) {
 132   std::string type;
 133   if (!jwk.GetString(kKeyTypeTag, &type) || type != kKeyTypeOct) {
 134     DVLOG(1) << "Missing or invalid '" << kKeyTypeTag << "': " << type;
 135     return false;
 136   }
 137
 138   // Get the key id and actual key parameters.
 139   std::string encoded_key_id;
 140   std::string encoded_key;
 141   if (!jwk.GetString(kKeyIdTag, &encoded_key_id)) {
 142     DVLOG(1) << "Missing '" << kKeyIdTag << "' parameter";
 143     return false;
 144   }
 145   if (!jwk.GetString(kKeyTag, &encoded_key)) {
 146     DVLOG(1) << "Missing '" << kKeyTag << "' parameter";
 147     return false;
 148   }
 149
 150   // Key ID and key are base64-encoded strings, so decode them.
 151   std::string raw_key_id = DecodeBase64Url(encoded_key_id);
 152   if (raw_key_id.empty()) {
 153     DVLOG(1) << "Invalid '" << kKeyIdTag << "' value: " << encoded_key_id;
 154     return false;
 155   }
 156
 157   std::string raw_key = DecodeBase64Url(encoded_key);
 158   if (raw_key.empty()) {
 159     DVLOG(1) << "Invalid '" << kKeyTag << "' value: " << encoded_key;
 160     return false;
 161   }
 162
 163   // Add the decoded key ID and the decoded key to the list.
 164   *jwk_key = std::make_pair(raw_key_id, raw_key);
 165   return true;
 166 }
 167
 168 bool ExtractKeysFromJWKSet(const std::string& jwk_set,
 169                            KeyIdAndKeyPairs* keys,
 170                            MediaKeys::SessionType* session_type) {
 171   if (!base::IsStringASCII(jwk_set)) {
 172     DVLOG(1) << "Non ASCII JWK Set: " << jwk_set;
 173     return false;
 174   }
 175
 176   scoped_ptr<base::Value> root(base::JSONReader().ReadToValue(jwk_set));
 177   if (!root.get() || root->GetType() != base::Value::TYPE_DICTIONARY) {
 178     DVLOG(1) << "Not valid JSON: " << jwk_set << ", root: " << root.get();
 179     return false;
 180   }
 181
 182   // Locate the set from the dictionary.
 183   base::DictionaryValue* dictionary =
 184       static_cast<base::DictionaryValue*>(root.get());
 185   base::ListValue* list_val = NULL;
 186   if (!dictionary->GetList(kKeysTag, &list_val)) {
 187     DVLOG(1) << "Missing '" << kKeysTag
 188              << "' parameter or not a list in JWK Set";
 189     return false;
 190   }
 191
 192   // Create a local list of keys, so that |jwk_keys| only gets updated on
 193   // success.
 194   KeyIdAndKeyPairs local_keys;
 195   for (size_t i = 0; i < list_val->GetSize(); ++i) {
 196     base::DictionaryValue* jwk = NULL;
 197     if (!list_val->GetDictionary(i, &jwk)) {
 198       DVLOG(1) << "Unable to access '" << kKeysTag << "'[" << i
 199                << "] in JWK Set";
 200       return false;
 201     }
 202     KeyIdAndKeyPair key_pair;
 203     if (!ConvertJwkToKeyPair(*jwk, &key_pair)) {
 204       DVLOG(1) << "Error from '" << kKeysTag << "'[" << i << "]";
 205       return false;
 206     }
 207     local_keys.push_back(key_pair);
 208   }
 209
 210   // Successfully processed all JWKs in the set. Now check if "type" is
 211   // specified.
 212   base::Value* value = NULL;
 213   std::string session_type_id;
 214   if (!dictionary->Get(kTypeTag, &value)) {
 215     // Not specified, so use the default type.
 216     *session_type = MediaKeys::TEMPORARY_SESSION;
 217   } else if (!value->GetAsString(&session_type_id)) {
 218     DVLOG(1) << "Invalid '" << kTypeTag << "' value";
 219     return false;
 220   } else if (session_type_id == kTemporarySession) {
 221     *session_type = MediaKeys::TEMPORARY_SESSION;
 222   } else if (session_type_id == kPersistentLicenseSession) {
 223     *session_type = MediaKeys::PERSISTENT_LICENSE_SESSION;
 224   } else if (session_type_id == kPersistentReleaseMessageSession) {
 225     *session_type = MediaKeys::PERSISTENT_RELEASE_MESSAGE_SESSION;
 226   } else {
 227     DVLOG(1) << "Invalid '" << kTypeTag << "' value: " << session_type_id;
 228     return false;
 229   }
 230
 231   // All done.
 232   keys->swap(local_keys);
 233   return true;
 234 }
 235
 236 bool ExtractKeyIdsFromKeyIdsInitData(const std::string& input,
 237                                      KeyIdList* key_ids,
 238                                      std::string* error_message) {
 239   if (!base::IsStringASCII(input)) {
 240     error_message->assign("Non ASCII: ");
 241     error_message->append(ShortenTo64Characters(input));
 242     return false;
 243   }
 244
 245   scoped_ptr<base::Value> root(base::JSONReader().ReadToValue(input));
 246   if (!root.get() || root->GetType() != base::Value::TYPE_DICTIONARY) {
 247     error_message->assign("Not valid JSON: ");
 248     error_message->append(ShortenTo64Characters(input));
 249     return false;
 250   }
 251
 252   // Locate the set from the dictionary.
 253   base::DictionaryValue* dictionary =
 254       static_cast<base::DictionaryValue*>(root.get());
 255   base::ListValue* list_val = NULL;
 256   if (!dictionary->GetList(kKeyIdsTag, &list_val)) {
 257     error_message->assign("Missing '");
 258     error_message->append(kKeyIdsTag);
 259     error_message->append("' parameter or not a list");
 260     return false;
 261   }
 262
 263   // Create a local list of key ids, so that |key_ids| only gets updated on
 264   // success.
 265   KeyIdList local_key_ids;
 266   for (size_t i = 0; i < list_val->GetSize(); ++i) {
 267     std::string encoded_key_id;
 268     if (!list_val->GetString(i, &encoded_key_id)) {
 269       error_message->assign("'");
 270       error_message->append(kKeyIdsTag);
 271       error_message->append("'[");
 272       error_message->append(base::UintToString(i));
 273       error_message->append("] is not string.");
 274       return false;
 275     }
 276
 277     // Key ID is a base64-encoded string, so decode it.
 278     std::string raw_key_id = DecodeBase64Url(encoded_key_id);
 279     if (raw_key_id.empty()) {
 280       error_message->assign("'");
 281       error_message->append(kKeyIdsTag);
 282       error_message->append("'[");
 283       error_message->append(base::UintToString(i));
 284       error_message->append("] is not valid base64url encoded. Value: ");
 285       error_message->append(ShortenTo64Characters(encoded_key_id));
 286       return false;
 287     }
 288
 289     // Add the decoded key ID to the list.
 290     local_key_ids.push_back(std::vector<uint8>(
 291         raw_key_id.data(), raw_key_id.data() + raw_key_id.length()));
 292   }
 293
 294   // All done.
 295   key_ids->swap(local_key_ids);
 296   error_message->clear();
 297   return true;
 298 }
 299
 300 void CreateLicenseRequest(const KeyIdList& key_ids,
 301                           MediaKeys::SessionType session_type,
 302                           std::vector<uint8>* license) {
 303   // Create the license request.
 304   scoped_ptr<base::DictionaryValue> request(new base::DictionaryValue());
 305   scoped_ptr<base::ListValue> list(new base::ListValue());
 306   for (const auto& key_id : key_ids)
 307     list->AppendString(EncodeBase64Url(&key_id[0], key_id.size()));
 308   request->Set(kKeyIdsTag, list.release());
 309
 310   switch (session_type) {
 311     case MediaKeys::TEMPORARY_SESSION:
 312       request->SetString(kTypeTag, kTemporarySession);
 313       break;
 314     case MediaKeys::PERSISTENT_LICENSE_SESSION:
 315       request->SetString(kTypeTag, kPersistentLicenseSession);
 316       break;
 317     case MediaKeys::PERSISTENT_RELEASE_MESSAGE_SESSION:
 318       request->SetString(kTypeTag, kPersistentReleaseMessageSession);
 319       break;
 320   }
 321
 322   // Serialize the license request as a string.
 323   std::string json;
 324   JSONStringValueSerializer serializer(&json);
 325   serializer.Serialize(*request);
 326
 327   // Convert the serialized license request into std::vector and return it.
 328   std::vector<uint8> result(json.begin(), json.end());
 329   license->swap(result);
 330 }
 331
 332 void CreateKeyIdsInitData(const KeyIdList& key_ids,
 333                           std::vector<uint8>* init_data) {
 334   // Create the init_data.
 335   scoped_ptr<base::DictionaryValue> dictionary(new base::DictionaryValue());
 336   scoped_ptr<base::ListValue> list(new base::ListValue());
 337   for (const auto& key_id : key_ids)
 338     list->AppendString(EncodeBase64Url(&key_id[0], key_id.size()));
 339   dictionary->Set(kKeyIdsTag, list.release());
 340
 341   // Serialize the dictionary as a string.
 342   std::string json;
 343   JSONStringValueSerializer serializer(&json);
 344   serializer.Serialize(*dictionary);
 345
 346   // Convert the serialized data into std::vector and return it.
 347   std::vector<uint8> result(json.begin(), json.end());
 348   init_data->swap(result);
 349 }
 350
 351 bool ExtractFirstKeyIdFromLicenseRequest(const std::vector<uint8>& license,
 352                                          std::vector<uint8>* first_key) {
 353   const std::string license_as_str(
 354       reinterpret_cast<const char*>(!license.empty() ? &license[0] : NULL),
 355       license.size());
 356   if (!base::IsStringASCII(license_as_str)) {
 357     DVLOG(1) << "Non ASCII license: " << license_as_str;
 358     return false;
 359   }
 360
 361   scoped_ptr<base::Value> root(base::JSONReader().ReadToValue(license_as_str));
 362   if (!root.get() || root->GetType() != base::Value::TYPE_DICTIONARY) {
 363     DVLOG(1) << "Not valid JSON: " << license_as_str;
 364     return false;
 365   }
 366
 367   // Locate the set from the dictionary.
 368   base::DictionaryValue* dictionary =
 369       static_cast<base::DictionaryValue*>(root.get());
 370   base::ListValue* list_val = NULL;
 371   if (!dictionary->GetList(kKeyIdsTag, &list_val)) {
 372     DVLOG(1) << "Missing '" << kKeyIdsTag << "' parameter or not a list";
 373     return false;
 374   }
 375
 376   // Get the first key.
 377   if (list_val->GetSize() < 1) {
 378     DVLOG(1) << "Empty '" << kKeyIdsTag << "' list";
 379     return false;
 380   }
 381
 382   std::string encoded_key;
 383   if (!list_val->GetString(0, &encoded_key)) {
 384     DVLOG(1) << "First entry in '" << kKeyIdsTag << "' not a string";
 385     return false;
 386   }
 387
 388   std::string decoded_string = DecodeBase64Url(encoded_key);
 389   if (decoded_string.empty()) {
 390     DVLOG(1) << "Invalid '" << kKeyIdsTag << "' value: " << encoded_key;
 391     return false;
 392   }
 393
 394   std::vector<uint8> result(decoded_string.begin(), decoded_string.end());
 395   first_key->swap(result);
 396   return true;
 397 }
 398
 399 }  // namespace media