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      1 /*
      2  * Copyright (C) 2014 The Android Open Source Project
      3  *
      4  * Licensed under the Apache License, Version 2.0 (the "License");
      5  * you may not use this file except in compliance with the License.
      6  * You may obtain a copy of the License at
      7  *
      8  *      http://www.apache.org/licenses/LICENSE-2.0
      9  *
     10  * Unless required by applicable law or agreed to in writing, software
     11  * distributed under the License is distributed on an "AS IS" BASIS,
     12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     13  * See the License for the specific language governing permissions and
     14  * limitations under the License.
     15  */
     16 
     17 //#define LOG_NDEBUG 0
     18 #define LOG_TAG "ClearKeyCryptoPlugin"
     19 #include <utils/Log.h>
     20 
     21 #include <openssl/aes.h>
     22 
     23 #include "AesCtrDecryptor.h"
     24 
     25 namespace clearkeydrm {
     26 
     27 static const size_t kBlockBitCount = kBlockSize * 8;
     28 
     29 android::status_t AesCtrDecryptor::decrypt(const android::Vector<uint8_t>& key,
     30         const Iv iv, const uint8_t* source,
     31         uint8_t* destination,
     32         const SubSample* subSamples,
     33         size_t numSubSamples,
     34         size_t* bytesDecryptedOut) {
     35     uint32_t blockOffset = 0;
     36     uint8_t previousEncryptedCounter[kBlockSize];
     37     memset(previousEncryptedCounter, 0, kBlockSize);
     38 
     39     if (key.size() != kBlockSize || (sizeof(Iv) / sizeof(uint8_t)) != kBlockSize) {
     40         android_errorWriteLog(0x534e4554, "63982768");
     41         return android::ERROR_DRM_DECRYPT;
     42     }
     43 
     44     size_t offset = 0;
     45     AES_KEY opensslKey;
     46     AES_set_encrypt_key(key.array(), kBlockBitCount, &opensslKey);
     47     Iv opensslIv;
     48     memcpy(opensslIv, iv, sizeof(opensslIv));
     49 
     50     for (size_t i = 0; i < numSubSamples; ++i) {
     51         const SubSample& subSample = subSamples[i];
     52 
     53         if (subSample.mNumBytesOfClearData > 0) {
     54             memcpy(destination + offset, source + offset,
     55                     subSample.mNumBytesOfClearData);
     56             offset += subSample.mNumBytesOfClearData;
     57         }
     58 
     59         if (subSample.mNumBytesOfEncryptedData > 0) {
     60             AES_ctr128_encrypt(source + offset, destination + offset,
     61                     subSample.mNumBytesOfEncryptedData, &opensslKey,
     62                     opensslIv, previousEncryptedCounter,
     63                     &blockOffset);
     64             offset += subSample.mNumBytesOfEncryptedData;
     65         }
     66     }
     67 
     68     *bytesDecryptedOut = offset;
     69     return android::OK;
     70 }
     71 
     72 } // namespace clearkeydrm
     73