1 /*
2 * Copyright 2015 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 "integrity_assured_key_blob.h"
18
19 #include <assert.h>
20
21 #include <keymaster/new>
22
23 #include <openssl/hmac.h>
24 #include <openssl/mem.h>
25
26 #include <keymaster/android_keymaster_utils.h>
27 #include <keymaster/authorization_set.h>
28
29 #include "openssl_err.h"
30
31 namespace keymaster {
32
33 static const uint8_t BLOB_VERSION = 0;
34 static const size_t HMAC_SIZE = 8;
35 static const char HMAC_KEY[] = "IntegrityAssuredBlob0";
36
min(size_t a,size_t b)37 inline size_t min(size_t a, size_t b) {
38 if (a < b)
39 return a;
40 return b;
41 }
42
43 class HmacCleanup {
44 public:
HmacCleanup(HMAC_CTX * ctx)45 explicit HmacCleanup(HMAC_CTX* ctx) : ctx_(ctx) {}
~HmacCleanup()46 ~HmacCleanup() { HMAC_CTX_cleanup(ctx_); }
47
48 private:
49 HMAC_CTX* ctx_;
50 };
51
ComputeHmac(const uint8_t * serialized_data,size_t serialized_data_size,const AuthorizationSet & hidden,uint8_t hmac[HMAC_SIZE])52 static keymaster_error_t ComputeHmac(const uint8_t* serialized_data, size_t serialized_data_size,
53 const AuthorizationSet& hidden, uint8_t hmac[HMAC_SIZE]) {
54 size_t hidden_bytes_size = hidden.SerializedSize();
55 UniquePtr<uint8_t[]> hidden_bytes(new (std::nothrow) uint8_t[hidden_bytes_size]);
56 if (!hidden_bytes.get())
57 return KM_ERROR_MEMORY_ALLOCATION_FAILED;
58 hidden.Serialize(hidden_bytes.get(), hidden_bytes.get() + hidden_bytes_size);
59
60 HMAC_CTX ctx;
61 HMAC_CTX_init(&ctx);
62 const EVP_MD* md = EVP_sha256();
63 if (!HMAC_Init_ex(&ctx, HMAC_KEY, sizeof(HMAC_KEY), md, NULL /* engine */))
64 return TranslateLastOpenSslError();
65 HmacCleanup cleanup(&ctx);
66
67 uint8_t tmp[EVP_MAX_MD_SIZE];
68 unsigned tmp_len;
69 if (!HMAC_Update(&ctx, serialized_data, serialized_data_size) ||
70 !HMAC_Update(&ctx, hidden_bytes.get(), hidden_bytes_size) || //
71 !HMAC_Final(&ctx, tmp, &tmp_len))
72 return TranslateLastOpenSslError();
73
74 assert(tmp_len >= HMAC_SIZE);
75 memcpy(hmac, tmp, min(HMAC_SIZE, tmp_len));
76
77 return KM_ERROR_OK;
78 }
79
SerializeIntegrityAssuredBlob(const KeymasterKeyBlob & key_material,const AuthorizationSet & hidden,const AuthorizationSet & hw_enforced,const AuthorizationSet & sw_enforced,KeymasterKeyBlob * key_blob)80 keymaster_error_t SerializeIntegrityAssuredBlob(const KeymasterKeyBlob& key_material,
81 const AuthorizationSet& hidden,
82 const AuthorizationSet& hw_enforced,
83 const AuthorizationSet& sw_enforced,
84 KeymasterKeyBlob* key_blob) {
85 size_t size = 1 /* version */ + //
86 key_material.SerializedSize() + //
87 hw_enforced.SerializedSize() + //
88 sw_enforced.SerializedSize() + //
89 HMAC_SIZE;
90
91 if (!key_blob->Reset(size))
92 return KM_ERROR_MEMORY_ALLOCATION_FAILED;
93
94 uint8_t* p = key_blob->writable_data();
95 *p++ = BLOB_VERSION;
96 p = key_material.Serialize(p, key_blob->end());
97 p = hw_enforced.Serialize(p, key_blob->end());
98 p = sw_enforced.Serialize(p, key_blob->end());
99
100 return ComputeHmac(key_blob->key_material, p - key_blob->key_material, hidden, p);
101 }
102
DeserializeIntegrityAssuredBlob(const KeymasterKeyBlob & key_blob,const AuthorizationSet & hidden,KeymasterKeyBlob * key_material,AuthorizationSet * hw_enforced,AuthorizationSet * sw_enforced)103 keymaster_error_t DeserializeIntegrityAssuredBlob(const KeymasterKeyBlob& key_blob,
104 const AuthorizationSet& hidden,
105 KeymasterKeyBlob* key_material,
106 AuthorizationSet* hw_enforced,
107 AuthorizationSet* sw_enforced) {
108 const uint8_t* p = key_blob.begin();
109 const uint8_t* end = key_blob.end();
110
111 if (p > end || p + HMAC_SIZE > end)
112 return KM_ERROR_INVALID_KEY_BLOB;
113
114 uint8_t computed_hmac[HMAC_SIZE];
115 keymaster_error_t error = ComputeHmac(key_blob.begin(), key_blob.key_material_size - HMAC_SIZE,
116 hidden, computed_hmac);
117 if (error != KM_ERROR_OK)
118 return error;
119
120 if (CRYPTO_memcmp(key_blob.end() - HMAC_SIZE, computed_hmac, HMAC_SIZE) != 0)
121 return KM_ERROR_INVALID_KEY_BLOB;
122
123 return DeserializeIntegrityAssuredBlob_NoHmacCheck(key_blob, key_material, hw_enforced,
124 sw_enforced);
125 }
126
DeserializeIntegrityAssuredBlob_NoHmacCheck(const KeymasterKeyBlob & key_blob,KeymasterKeyBlob * key_material,AuthorizationSet * hw_enforced,AuthorizationSet * sw_enforced)127 keymaster_error_t DeserializeIntegrityAssuredBlob_NoHmacCheck(const KeymasterKeyBlob& key_blob,
128 KeymasterKeyBlob* key_material,
129 AuthorizationSet* hw_enforced,
130 AuthorizationSet* sw_enforced) {
131 const uint8_t* p = key_blob.begin();
132 const uint8_t* end = key_blob.end() - HMAC_SIZE;
133
134 if (p > end)
135 return KM_ERROR_INVALID_KEY_BLOB;
136
137 if (*p != BLOB_VERSION)
138 return KM_ERROR_INVALID_KEY_BLOB;
139 ++p;
140
141 if (!key_material->Deserialize(&p, end) || //
142 !hw_enforced->Deserialize(&p, end) || //
143 !sw_enforced->Deserialize(&p, end))
144 return KM_ERROR_INVALID_KEY_BLOB;
145
146 return KM_ERROR_OK;
147 }
148
149 } // namespace keymaster;
150