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
decrypt(const android::Vector<uint8_t> & key,const Iv iv,const uint8_t * source,uint8_t * destination,const SubSample * subSamples,size_t numSubSamples,size_t * bytesDecryptedOut)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