AesCtrDecryptor.cpp revision 16dfdcff6e4bb025220b88d5fc132ae48e7cb437 
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
25namespace clearkeydrm {
26
27static const size_t kBlockBitCount = kBlockSize * 8;
28
29android::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    size_t offset = 0;
40    AES_KEY opensslKey;
41    AES_set_encrypt_key(key.array(), kBlockBitCount, &opensslKey);
42    Iv opensslIv;
43    memcpy(opensslIv, iv, sizeof(opensslIv));
44
45    for (size_t i = 0; i < numSubSamples; ++i) {
46        const SubSample& subSample = subSamples[i];
47
48        if (subSample.mNumBytesOfClearData > 0) {
49            memcpy(destination + offset, source + offset,
50                    subSample.mNumBytesOfClearData);
51            offset += subSample.mNumBytesOfClearData;
52        }
53
54        if (subSample.mNumBytesOfEncryptedData > 0) {
55            AES_ctr128_encrypt(source + offset, destination + offset,
56                    subSample.mNumBytesOfEncryptedData, &opensslKey,
57                    opensslIv, previousEncryptedCounter,
58                    &blockOffset);
59            offset += subSample.mNumBytesOfEncryptedData;
60        }
61    }
62
63    *bytesDecryptedOut = offset;
64    return android::OK;
65}
66
67} // namespace clearkeydrm
68