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 "ocb_utils.h"
18
19 #include <assert.h>
20
21 #include <new>
22
23 #include <openssl/aes.h>
24 #include <openssl/sha.h>
25
26 #include <hardware/keymaster_defs.h>
27 #include <keymaster/authorization_set.h>
28 #include <keymaster/android_keymaster_utils.h>
29
30 #include "openssl_err.h"
31
32 namespace keymaster {
33
34 class AeCtx {
35 public:
AeCtx()36 AeCtx() : ctx_(ae_allocate(NULL)) {}
~AeCtx()37 ~AeCtx() {
38 ae_clear(ctx_);
39 ae_free(ctx_);
40 }
41
get()42 ae_ctx* get() { return ctx_; }
43
44 private:
45 ae_ctx* ctx_;
46 };
47
BuildDerivationData(const AuthorizationSet & hw_enforced,const AuthorizationSet & sw_enforced,const AuthorizationSet & hidden,UniquePtr<uint8_t[]> * derivation_data,size_t * derivation_data_length)48 static keymaster_error_t BuildDerivationData(const AuthorizationSet& hw_enforced,
49 const AuthorizationSet& sw_enforced,
50 const AuthorizationSet& hidden,
51 UniquePtr<uint8_t[]>* derivation_data,
52 size_t* derivation_data_length) {
53 *derivation_data_length =
54 hidden.SerializedSize() + hw_enforced.SerializedSize() + sw_enforced.SerializedSize();
55 derivation_data->reset(new (std::nothrow) uint8_t[*derivation_data_length]);
56 if (!derivation_data->get())
57 return KM_ERROR_MEMORY_ALLOCATION_FAILED;
58
59 uint8_t* buf = derivation_data->get();
60 uint8_t* end = derivation_data->get() + *derivation_data_length;
61 buf = hidden.Serialize(buf, end);
62 buf = hw_enforced.Serialize(buf, end);
63 buf = sw_enforced.Serialize(buf, end);
64
65 return KM_ERROR_OK;
66 }
67
InitializeKeyWrappingContext(const AuthorizationSet & hw_enforced,const AuthorizationSet & sw_enforced,const AuthorizationSet & hidden,const KeymasterKeyBlob & master_key,AeCtx * ctx)68 static keymaster_error_t InitializeKeyWrappingContext(const AuthorizationSet& hw_enforced,
69 const AuthorizationSet& sw_enforced,
70 const AuthorizationSet& hidden,
71 const KeymasterKeyBlob& master_key,
72 AeCtx* ctx) {
73 size_t derivation_data_length;
74 UniquePtr<uint8_t[]> derivation_data;
75 keymaster_error_t error = BuildDerivationData(hw_enforced, sw_enforced, hidden,
76 &derivation_data, &derivation_data_length);
77 if (error != KM_ERROR_OK)
78 return error;
79
80 SHA256_CTX sha256_ctx;
81 UniquePtr<uint8_t[]> hash_buf(new (std::nothrow) uint8_t[SHA256_DIGEST_LENGTH]);
82 if (!hash_buf.get())
83 return KM_ERROR_MEMORY_ALLOCATION_FAILED;
84 Eraser hash_eraser(hash_buf.get(), SHA256_DIGEST_LENGTH);
85 UniquePtr<uint8_t[]> derived_key(new (std::nothrow) uint8_t[AES_BLOCK_SIZE]);
86 if (!derived_key.get())
87 return KM_ERROR_MEMORY_ALLOCATION_FAILED;
88 Eraser derived_key_eraser(derived_key.get(), AES_BLOCK_SIZE);
89
90 if (!ctx->get() || !hash_buf.get() || !derived_key.get())
91 return KM_ERROR_MEMORY_ALLOCATION_FAILED;
92
93 // Hash derivation data.
94 Eraser sha256_ctx_eraser(sha256_ctx);
95 SHA256_Init(&sha256_ctx);
96 SHA256_Update(&sha256_ctx, derivation_data.get(), derivation_data_length);
97 SHA256_Final(hash_buf.get(), &sha256_ctx);
98
99 // Encrypt hash with master key to build derived key.
100 AES_KEY aes_key;
101 Eraser aes_key_eraser(AES_KEY);
102 if (0 !=
103 AES_set_encrypt_key(master_key.key_material, master_key.key_material_size * 8, &aes_key))
104 return TranslateLastOpenSslError();
105
106 AES_encrypt(hash_buf.get(), derived_key.get(), &aes_key);
107
108 // Set up AES OCB context using derived key.
109 if (ae_init(ctx->get(), derived_key.get(), AES_BLOCK_SIZE /* key length */, OCB_NONCE_LENGTH,
110 OCB_TAG_LENGTH) != AE_SUCCESS) {
111 memset_s(ctx->get(), 0, ae_ctx_sizeof());
112 return KM_ERROR_UNKNOWN_ERROR;
113 }
114
115 return KM_ERROR_OK;
116 }
117
OcbEncryptKey(const AuthorizationSet & hw_enforced,const AuthorizationSet & sw_enforced,const AuthorizationSet & hidden,const KeymasterKeyBlob & master_key,const KeymasterKeyBlob & plaintext,const Buffer & nonce,KeymasterKeyBlob * ciphertext,Buffer * tag)118 keymaster_error_t OcbEncryptKey(const AuthorizationSet& hw_enforced,
119 const AuthorizationSet& sw_enforced, const AuthorizationSet& hidden,
120 const KeymasterKeyBlob& master_key,
121 const KeymasterKeyBlob& plaintext, const Buffer& nonce,
122 KeymasterKeyBlob* ciphertext, Buffer* tag) {
123 assert(ciphertext && tag);
124
125 if (nonce.available_read() != OCB_NONCE_LENGTH)
126 return KM_ERROR_INVALID_ARGUMENT;
127
128 AeCtx ctx;
129 if (!ctx.get())
130 return KM_ERROR_MEMORY_ALLOCATION_FAILED;
131
132 keymaster_error_t error =
133 InitializeKeyWrappingContext(hw_enforced, sw_enforced, hidden, master_key, &ctx);
134 if (error != KM_ERROR_OK)
135 return error;
136
137 if (!ciphertext->Reset(plaintext.key_material_size))
138 return KM_ERROR_MEMORY_ALLOCATION_FAILED;
139
140 int ae_err = ae_encrypt(ctx.get(), nonce.peek_read(), plaintext.key_material,
141 plaintext.key_material_size, NULL /* additional data */,
142 0 /* additional data length */, ciphertext->writable_data(),
143 tag->peek_write(), 1 /* final */);
144 if (ae_err < 0) {
145 LOG_E("Error %d while encrypting key", ae_err);
146 return KM_ERROR_UNKNOWN_ERROR;
147 }
148 if (!tag->advance_write(OCB_TAG_LENGTH))
149 return KM_ERROR_UNKNOWN_ERROR;
150 assert(ae_err == static_cast<int>(plaintext.key_material_size));
151 return KM_ERROR_OK;
152 }
153
OcbDecryptKey(const AuthorizationSet & hw_enforced,const AuthorizationSet & sw_enforced,const AuthorizationSet & hidden,const KeymasterKeyBlob & master_key,const KeymasterKeyBlob & ciphertext,const Buffer & nonce,const Buffer & tag,KeymasterKeyBlob * plaintext)154 keymaster_error_t OcbDecryptKey(const AuthorizationSet& hw_enforced,
155 const AuthorizationSet& sw_enforced, const AuthorizationSet& hidden,
156 const KeymasterKeyBlob& master_key,
157 const KeymasterKeyBlob& ciphertext, const Buffer& nonce,
158 const Buffer& tag, KeymasterKeyBlob* plaintext) {
159 assert(plaintext);
160
161 if (nonce.available_read() != OCB_NONCE_LENGTH || tag.available_read() != OCB_TAG_LENGTH)
162 return KM_ERROR_INVALID_ARGUMENT;
163
164 AeCtx ctx;
165 if (!ctx.get())
166 return KM_ERROR_MEMORY_ALLOCATION_FAILED;
167
168 keymaster_error_t error =
169 InitializeKeyWrappingContext(hw_enforced, sw_enforced, hidden, master_key, &ctx);
170 if (error != KM_ERROR_OK)
171 return error;
172
173 if (!plaintext->Reset(ciphertext.key_material_size))
174 return KM_ERROR_MEMORY_ALLOCATION_FAILED;
175
176 int ae_err = ae_decrypt(ctx.get(), nonce.peek_read(), ciphertext.key_material,
177 ciphertext.key_material_size, NULL /* additional data */,
178 0 /* additional data length */, plaintext->writable_data(),
179 tag.peek_read(), 1 /* final */);
180 if (ae_err == AE_INVALID) {
181 // Authentication failed! Decryption probably succeeded(ish), but we don't want to return
182 // any data when the authentication fails, so clear it.
183 plaintext->Clear();
184 LOG_E("Failed to validate authentication tag during key decryption", 0);
185 return KM_ERROR_INVALID_KEY_BLOB;
186 } else if (ae_err < 0) {
187 LOG_E("Failed to decrypt key, error: %d", ae_err);
188 return KM_ERROR_UNKNOWN_ERROR;
189 }
190 assert(ae_err == static_cast<int>(ciphertext.key_material_size));
191 return KM_ERROR_OK;
192 }
193
194 } // namespace keymaster
195