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 
30 inline uint32_t div_round_up(uint32_t dividend, uint32_t divisor) {
31     return (dividend + divisor - 1) / divisor;
32 }
33 
34 size_t min(size_t a, size_t b) {
35     return a < b ? a : b;
36 }
37 
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