1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
|
/*
* Copyright 2015 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#ifndef SYSTEM_KEYMASTER_HKDF_H_
#define SYSTEM_KEYMASTER_HKDF_H_
#include <keymaster/serializable.h>
namespace keymaster {
// Rfc5869HmacSha256Kdf implements the key derivation function specified in RFC 5869 (using
// SHA256) and outputs key material, as needed by ECIES.
// See https://tools.ietf.org/html/rfc5869 for details.
class Rfc5869HmacSha256Kdf {
public:
// |secret|: the input shared secret (or, from RFC 5869, the IKM).
// |salt|: an (optional) public salt / non-secret random value. While
// optional, callers are strongly recommended to provide a salt. There is no
// added security value in making this larger than the SHA-256 block size of
// 64 bytes.
// |info|: an (optional) label to distinguish different uses of HKDF. It is
// optional context and application specific information (can be a zero-length
// string).
// |key_bytes_to_generate|: the number of bytes of key material to generate.
Rfc5869HmacSha256Kdf(Buffer& secret, Buffer& salt, Buffer& info, size_t key_bytes_to_generate);
Rfc5869HmacSha256Kdf(const uint8_t* secret, size_t secret_len, const uint8_t* salt,
size_t salt_len, const uint8_t* info, size_t info_len,
size_t key_bytes_to_generate);
void secret_key(Buffer* buf) const {
buf->Reinitialize(secret_key_.peek_read(), secret_key_.available_read());
}
private:
Buffer output_;
Buffer secret_key_;
};
} // namespace keymaster
#endif // SYSTEM_KEYMASTER_HKDF_H_
|