1 /*
2 * Copyright 2017 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 <keymaster/km_openssl/ckdf.h>
18
19 #include <assert.h>
20
21 #include <openssl/aes.h>
22 #include <openssl/cmac.h>
23
24 #include <keymaster/km_openssl/openssl_err.h>
25 #include <keymaster/km_openssl/openssl_utils.h>
26 #include <keymaster/serializable.h>
27
28 namespace keymaster {
29
div_round_up(uint32_t dividend,uint32_t divisor)30 inline uint32_t div_round_up(uint32_t dividend, uint32_t divisor) {
31 return (dividend + divisor - 1) / divisor;
32 }
33
min(size_t a,size_t b)34 size_t min(size_t a, size_t b) {
35 return a < b ? a : b;
36 }
37
DEFINE_OPENSSL_OBJECT_POINTER(CMAC_CTX)38 DEFINE_OPENSSL_OBJECT_POINTER(CMAC_CTX)
39
40 keymaster_error_t ckdf(const KeymasterKeyBlob& key, const KeymasterBlob& label,
41 const keymaster_blob_t* context_chunks, size_t num_chunks,
42 KeymasterKeyBlob* output) {
43 // Note: the variables i and L correspond to i and L in the standard. See page 12 of
44 // http://nvlpubs.nist.gov/nistpubs/Legacy/SP/nistspecialpublication800-108.pdf.
45
46 const uint32_t blocks = div_round_up(output->key_material_size, AES_BLOCK_SIZE);
47 const uint32_t L = output->key_material_size * 8; // bits
48 const uint32_t net_order_L = hton(L);
49
50 CMAC_CTX_Ptr ctx(CMAC_CTX_new());
51 if (!ctx.get()) return KM_ERROR_MEMORY_ALLOCATION_FAILED;
52
53 auto algo = EVP_aes_128_cbc();
54 switch (key.key_material_size) {
55 case AES_BLOCK_SIZE:
56 /* Already set */
57 break;
58 case AES_BLOCK_SIZE * 2:
59 algo = EVP_aes_256_cbc();
60 break;
61 default:
62 return KM_ERROR_UNSUPPORTED_KEY_SIZE;
63 }
64
65 if (!CMAC_Init(ctx.get(), key.key_material, key.key_material_size, algo,
66 nullptr /* engine */)) {
67 return TranslateLastOpenSslError();
68 }
69
70 auto output_pos = const_cast<uint8_t*>(output->begin());
71 memset(output_pos, 0, output->key_material_size);
72 for (uint32_t i = 1; i <= blocks; ++i) {
73 // Data to mac is i || label || 0x00 || context || L, with i and L represented in 32 bits,
74 // in network order.
75
76 // i
77 uint32_t net_order_i = hton(i);
78 if (!CMAC_Update(ctx.get(), reinterpret_cast<uint8_t*>(&net_order_i),
79 sizeof(net_order_i))) {
80 return TranslateLastOpenSslError();
81 }
82
83 // label
84 if (!CMAC_Update(ctx.get(), label.data, label.data_length)) {
85 return TranslateLastOpenSslError();
86 }
87
88 // 0x00
89 uint8_t zero = 0;
90 if (!CMAC_Update(ctx.get(), &zero, sizeof(zero))) return TranslateLastOpenSslError();
91
92 // context
93 for (size_t chunk = 0; chunk < num_chunks; ++chunk) {
94 if (!CMAC_Update(ctx.get(), context_chunks[chunk].data,
95 context_chunks[chunk].data_length)) {
96 return TranslateLastOpenSslError();
97 }
98 }
99
100 // L
101 uint8_t buf[4];
102 memcpy(buf, &net_order_L, 4);
103 if (!CMAC_Update(ctx.get(), buf, sizeof(buf))) TranslateLastOpenSslError();
104
105 size_t out_len;
106 if (output_pos <= output->end() - AES_BLOCK_SIZE) {
107 if (!CMAC_Final(ctx.get(), output_pos, &out_len)) return TranslateLastOpenSslError();
108 output_pos += out_len;
109 } else {
110 uint8_t cmac[AES_BLOCK_SIZE];
111 if (!CMAC_Final(ctx.get(), cmac, &out_len)) return TranslateLastOpenSslError();
112 size_t to_copy = output->end() - output_pos;
113 memcpy(output_pos, cmac, to_copy);
114 output_pos += to_copy;
115 }
116
117 CMAC_Reset(ctx.get());
118 }
119 assert(output_pos == output->end());
120
121 return KM_ERROR_OK;
122 }
123
124 } // namespace keymaster
125