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