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_util.h"
  14 #include "base/values.h"
  15
  16 namespace media {
  17
  18 const char kKeysTag[] = "keys";
  19 const char kKeyTypeTag[] = "kty";
  20 const char kSymmetricKeyValue[] = "oct";
  21 const char kKeyTag[] = "k";
  22 const char kKeyIdTag[] = "kid";
  23 const char kKeyIdsTag[] = "kids";
  24 const char kBase64Padding = '=';
  25 const char kTypeTag[] = "type";
  26 const char kPersistentType[] = "persistent";
  27 const char kTemporaryType[] = "temporary";
  28
  29 // Encodes |input| into a base64 string without padding.
  30 static std::string EncodeBase64(const uint8* input, int input_length) {
  31   std::string encoded_text;
  32   base::Base64Encode(
  33       std::string(reinterpret_cast<const char*>(input), input_length),
  34       &encoded_text);
  35
  36   // Remove any padding characters added by Base64Encode().
  37   size_t found = encoded_text.find_last_not_of(kBase64Padding);
  38   if (found != std::string::npos)
  39     encoded_text.erase(found + 1);
  40
  41   return encoded_text;
  42 }
  43
  44 // Decodes an unpadded base64 string. Returns empty string on error.
  45 static std::string DecodeBase64(const std::string& encoded_text) {
  46   // EME spec doesn't allow padding characters.
  47   if (encoded_text.find_first_of(kBase64Padding) != std::string::npos)
  48     return std::string();
  49
  50   // Since base::Base64Decode() requires padding characters, add them so length
  51   // of |encoded_text| is exactly a multiple of 4.
  52   size_t num_last_grouping_chars = encoded_text.length() % 4;
  53   std::string modified_text = encoded_text;
  54   if (num_last_grouping_chars > 0)
  55     modified_text.append(4 - num_last_grouping_chars, kBase64Padding);
  56
  57   std::string decoded_text;
  58   if (!base::Base64Decode(modified_text, &decoded_text))
  59     return std::string();
  60
  61   return decoded_text;
  62 }
  63
  64 std::string GenerateJWKSet(const uint8* key, int key_length,
  65                            const uint8* key_id, int key_id_length) {
  66   // Both |key| and |key_id| need to be base64 encoded strings in the JWK.
  67   std::string key_base64 = EncodeBase64(key, key_length);
  68   std::string key_id_base64 = EncodeBase64(key_id, key_id_length);
  69
  70   // Create the JWK, and wrap it into a JWK Set.
  71   scoped_ptr<base::DictionaryValue> jwk(new base::DictionaryValue());
  72   jwk->SetString(kKeyTypeTag, kSymmetricKeyValue);
  73   jwk->SetString(kKeyTag, key_base64);
  74   jwk->SetString(kKeyIdTag, key_id_base64);
  75   scoped_ptr<base::ListValue> list(new base::ListValue());
  76   list->Append(jwk.release());
  77   base::DictionaryValue jwk_set;
  78   jwk_set.Set(kKeysTag, list.release());
  79
  80   // Finally serialize |jwk_set| into a string and return it.
  81   std::string serialized_jwk;
  82   JSONStringValueSerializer serializer(&serialized_jwk);
  83   serializer.Serialize(jwk_set);
  84   return serialized_jwk;
  85 }
  86
  87 // Processes a JSON Web Key to extract the key id and key value. Sets |jwk_key|
  88 // to the id/value pair and returns true on success.
  89 static bool ConvertJwkToKeyPair(const base::DictionaryValue& jwk,
  90                                 KeyIdAndKeyPair* jwk_key) {
  91   // Have found a JWK, start by checking that it is a symmetric key.
  92   std::string type;
  93   if (!jwk.GetString(kKeyTypeTag, &type) || type != kSymmetricKeyValue) {
  94     DVLOG(1) << "JWK is not a symmetric key";
  95     return false;
  96   }
  97
  98   // Get the key id and actual key parameters.
  99   std::string encoded_key_id;
 100   std::string encoded_key;
 101   if (!jwk.GetString(kKeyIdTag, &encoded_key_id)) {
 102     DVLOG(1) << "Missing '" << kKeyIdTag << "' parameter";
 103     return false;
 104   }
 105   if (!jwk.GetString(kKeyTag, &encoded_key)) {
 106     DVLOG(1) << "Missing '" << kKeyTag << "' parameter";
 107     return false;
 108   }
 109
 110   // Key ID and key are base64-encoded strings, so decode them.
 111   std::string raw_key_id = DecodeBase64(encoded_key_id);
 112   if (raw_key_id.empty()) {
 113     DVLOG(1) << "Invalid '" << kKeyIdTag << "' value: " << encoded_key_id;
 114     return false;
 115   }
 116
 117   std::string raw_key = DecodeBase64(encoded_key);
 118   if (raw_key.empty()) {
 119     DVLOG(1) << "Invalid '" << kKeyTag << "' value: " << encoded_key;
 120     return false;
 121   }
 122
 123   // Add the decoded key ID and the decoded key to the list.
 124   *jwk_key = std::make_pair(raw_key_id, raw_key);
 125   return true;
 126 }
 127
 128 bool ExtractKeysFromJWKSet(const std::string& jwk_set,
 129                            KeyIdAndKeyPairs* keys,
 130                            MediaKeys::SessionType* session_type) {
 131   if (!base::IsStringASCII(jwk_set))
 132     return false;
 133
 134   scoped_ptr<base::Value> root(base::JSONReader().ReadToValue(jwk_set));
 135   if (!root.get() || root->GetType() != base::Value::TYPE_DICTIONARY)
 136     return false;
 137
 138   // Locate the set from the dictionary.
 139   base::DictionaryValue* dictionary =
 140       static_cast<base::DictionaryValue*>(root.get());
 141   base::ListValue* list_val = NULL;
 142   if (!dictionary->GetList(kKeysTag, &list_val)) {
 143     DVLOG(1) << "Missing '" << kKeysTag
 144              << "' parameter or not a list in JWK Set";
 145     return false;
 146   }
 147
 148   // Create a local list of keys, so that |jwk_keys| only gets updated on
 149   // success.
 150   KeyIdAndKeyPairs local_keys;
 151   for (size_t i = 0; i < list_val->GetSize(); ++i) {
 152     base::DictionaryValue* jwk = NULL;
 153     if (!list_val->GetDictionary(i, &jwk)) {
 154       DVLOG(1) << "Unable to access '" << kKeysTag << "'[" << i
 155                << "] in JWK Set";
 156       return false;
 157     }
 158     KeyIdAndKeyPair key_pair;
 159     if (!ConvertJwkToKeyPair(*jwk, &key_pair)) {
 160       DVLOG(1) << "Error from '" << kKeysTag << "'[" << i << "]";
 161       return false;
 162     }
 163     local_keys.push_back(key_pair);
 164   }
 165
 166   // Successfully processed all JWKs in the set. Now check if "type" is
 167   // specified.
 168   base::Value* value = NULL;
 169   std::string type_id;
 170   if (!dictionary->Get(kTypeTag, &value)) {
 171     // Not specified, so use the default type.
 172     *session_type = MediaKeys::TEMPORARY_SESSION;
 173   } else if (!value->GetAsString(&type_id)) {
 174     DVLOG(1) << "Invalid '" << kTypeTag << "' value";
 175     return false;
 176   } else if (type_id == kPersistentType) {
 177     *session_type = MediaKeys::PERSISTENT_SESSION;
 178   } else if (type_id == kTemporaryType) {
 179     *session_type = MediaKeys::TEMPORARY_SESSION;
 180   } else {
 181     DVLOG(1) << "Invalid '" << kTypeTag << "' value: " << type_id;
 182     return false;
 183   }
 184
 185   // All done.
 186   keys->swap(local_keys);
 187   return true;
 188 }
 189
 190 void CreateLicenseRequest(const uint8* key_id,
 191                           int key_id_length,
 192                           MediaKeys::SessionType session_type,
 193                           std::vector<uint8>* license) {
 194   // Create the license request.
 195   scoped_ptr<base::DictionaryValue> request(new base::DictionaryValue());
 196   scoped_ptr<base::ListValue> list(new base::ListValue());
 197   list->AppendString(EncodeBase64(key_id, key_id_length));
 198   request->Set(kKeyIdsTag, list.release());
 199
 200   switch (session_type) {
 201     case MediaKeys::TEMPORARY_SESSION:
 202       request->SetString(kTypeTag, kTemporaryType);
 203       break;
 204     case MediaKeys::PERSISTENT_SESSION:
 205       request->SetString(kTypeTag, kPersistentType);
 206       break;
 207   }
 208
 209   // Serialize the license request as a string.
 210   std::string json;
 211   JSONStringValueSerializer serializer(&json);
 212   serializer.Serialize(*request);
 213
 214   // Convert the serialized license request into std::vector and return it.
 215   std::vector<uint8> result(json.begin(), json.end());
 216   license->swap(result);
 217 }
 218
 219 bool ExtractFirstKeyIdFromLicenseRequest(const std::vector<uint8>& license,
 220                                          std::vector<uint8>* first_key) {
 221   const std::string license_as_str(
 222       reinterpret_cast<const char*>(!license.empty() ? &license[0] : NULL),
 223       license.size());
 224   if (!base::IsStringASCII(license_as_str))
 225     return false;
 226
 227   scoped_ptr<base::Value> root(base::JSONReader().ReadToValue(license_as_str));
 228   if (!root.get() || root->GetType() != base::Value::TYPE_DICTIONARY)
 229     return false;
 230
 231   // Locate the set from the dictionary.
 232   base::DictionaryValue* dictionary =
 233       static_cast<base::DictionaryValue*>(root.get());
 234   base::ListValue* list_val = NULL;
 235   if (!dictionary->GetList(kKeyIdsTag, &list_val)) {
 236     DVLOG(1) << "Missing '" << kKeyIdsTag << "' parameter or not a list";
 237     return false;
 238   }
 239
 240   // Get the first key.
 241   if (list_val->GetSize() < 1) {
 242     DVLOG(1) << "Empty '" << kKeyIdsTag << "' list";
 243     return false;
 244   }
 245
 246   std::string encoded_key;
 247   if (!list_val->GetString(0, &encoded_key)) {
 248     DVLOG(1) << "First entry in '" << kKeyIdsTag << "' not a string";
 249     return false;
 250   }
 251
 252   std::string decoded_string = DecodeBase64(encoded_key);
 253   if (decoded_string.empty()) {
 254     DVLOG(1) << "Invalid '" << kKeyIdsTag << "' value: " << encoded_key;
 255     return false;
 256   }
 257
 258   std::vector<uint8> result(decoded_string.begin(), decoded_string.end());
 259   first_key->swap(result);
 260   return true;
 261 }
 262
 263 }  // namespace media