1 /*
2 * Copyright (C) 2020 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 #include <gtest/gtest.h>
18 #include <openssl/cipher.h>
19 #include <openssl/evp.h>
20 #include <string.h>
21
22 #include "vts_kernel_encryption.h"
23
24 namespace android {
25 namespace kernel {
26
DoXtsMasking(uint8_t * data,int num_blocks,const uint8_t tweak[kAesBlockSize])27 static void DoXtsMasking(uint8_t *data, int num_blocks,
28 const uint8_t tweak[kAesBlockSize]) {
29 uint8_t mask[kAesBlockSize];
30
31 memcpy(mask, tweak, kAesBlockSize);
32
33 for (int i = 0; i < num_blocks; i++) {
34 // XOR the next block with the current mask.
35 for (int j = 0; j < kAesBlockSize; j++) {
36 data[i * kAesBlockSize + j] ^= mask[j];
37 }
38 // Multipy the mask by 'x' in GF(2^128).
39 int carry = 0;
40 for (int j = 0; j < kAesBlockSize; j++) {
41 int next_carry = mask[j] >> 7;
42
43 mask[j] = (mask[j] << 1) ^ carry;
44 carry = next_carry;
45 }
46 if (carry != 0) {
47 mask[0] ^= 0x87;
48 }
49 }
50 }
51
DoEncrypt(const uint8_t key[kAes256XtsKeySize],const uint8_t iv[kAesBlockSize],const uint8_t * src,uint8_t * dst,int nbytes) const52 bool Aes256XtsCipher::DoEncrypt(const uint8_t key[kAes256XtsKeySize],
53 const uint8_t iv[kAesBlockSize],
54 const uint8_t *src, uint8_t *dst,
55 int nbytes) const {
56 std::unique_ptr<EVP_CIPHER_CTX, void (*)(EVP_CIPHER_CTX *)> ctx(
57 EVP_CIPHER_CTX_new(), EVP_CIPHER_CTX_free);
58 int outl;
59
60 if (ctx == nullptr) {
61 ADD_FAILURE() << "Failed to allocate BoringSSL cipher context";
62 return false;
63 }
64 if (nbytes % kAesBlockSize != 0) {
65 ADD_FAILURE() << "Bad input size";
66 return false;
67 }
68
69 // For some reason, BoringSSL considers AES-256-XTS to be deprecated, and it's
70 // in a directory of deprecated algorithms that's not compiled on Android.
71 // AES-256-ECB is still available though, so just implement XTS manually...
72
73 // Encrypt the IV. This uses the second half of the AES-256-XTS key.
74 uint8_t tweak[kAesBlockSize];
75 if (EVP_EncryptInit_ex(ctx.get(), EVP_aes_256_ecb(), nullptr,
76 key + kAes256KeySize, nullptr) != 1) {
77 ADD_FAILURE() << "Failed to initialize BoringSSL AES context";
78 return false;
79 }
80 if (EVP_EncryptUpdate(ctx.get(), tweak, &outl, iv, kAesBlockSize) != 1 ||
81 outl != kAesBlockSize) {
82 ADD_FAILURE() << "BoringSSL AES encryption failed (tweak)";
83 return false;
84 }
85
86 // Copy plaintext to output buffer, so that we can just transform it in-place.
87 memmove(dst, src, nbytes);
88
89 // Mask the data pre-encryption.
90 DoXtsMasking(dst, nbytes / kAesBlockSize, tweak);
91
92 // Encrypt the data.
93 if (EVP_EncryptInit_ex(ctx.get(), EVP_aes_256_ecb(), nullptr, key, nullptr) !=
94 1) {
95 ADD_FAILURE() << "Failed to reinitialize BoringSSL AES context";
96 return false;
97 }
98 if (EVP_EncryptUpdate(ctx.get(), dst, &outl, dst, nbytes) != 1 ||
99 outl != nbytes) {
100 ADD_FAILURE() << "BoringSSL AES encryption failed (data)";
101 return false;
102 }
103 // Mask the data post-encryption.
104 DoXtsMasking(dst, nbytes / kAesBlockSize, tweak);
105 return true;
106 }
107
108 } // namespace kernel
109 } // namespace android
110