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Thai Duong7689ed62015-03-20 16:50:18 -07001/*
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 "hmac.h"
18#include "hkdf.h"
19
20#include <assert.h>
Thai Duong7689ed62015-03-20 16:50:18 -070021
22namespace keymaster {
23
24const size_t kSHA256HashLength = 32;
25
26Rfc5869HmacSha256Kdf::Rfc5869HmacSha256Kdf(Buffer& secret, Buffer& salt, Buffer& info,
Thai Duong60eebdc2015-03-25 17:20:24 -070027 size_t key_bytes_to_generate, keymaster_error_t* error) {
Thai Duong7689ed62015-03-20 16:50:18 -070028 Rfc5869HmacSha256Kdf(secret.peek_read(), secret.available_read(), salt.peek_read(),
29 salt.available_read(), info.peek_read(), info.available_read(),
Thai Duong60eebdc2015-03-25 17:20:24 -070030 key_bytes_to_generate, error);
Thai Duong7689ed62015-03-20 16:50:18 -070031}
32
33Rfc5869HmacSha256Kdf::Rfc5869HmacSha256Kdf(const uint8_t* secret, size_t secret_len,
34 const uint8_t* salt, size_t salt_len,
35 const uint8_t* info, size_t info_len,
Thai Duong60eebdc2015-03-25 17:20:24 -070036 size_t key_bytes_to_generate, keymaster_error_t* error) {
Thai Duong7689ed62015-03-20 16:50:18 -070037 // Step 1. Extract: PRK = HMAC-SHA256(actual_salt, secret)
38 // https://tools.ietf.org/html/rfc5869#section-2.2
39 HmacSha256 prk_hmac;
Thai Duong60eebdc2015-03-25 17:20:24 -070040 bool result;
41 if (salt) {
42 result = prk_hmac.Init(salt, salt_len);
43 } else {
44 uint8_t zeros[kSHA256HashLength];
45 // If salt is not given, HashLength zeros are used.
46 memset(zeros, 0, sizeof(zeros));
47 result = prk_hmac.Init(zeros, sizeof(zeros));
48 }
Thai Duong7689ed62015-03-20 16:50:18 -070049 assert(result);
Chad Brubaker3e37f0a2015-06-03 10:39:00 -070050 // avoid the unused variable warning if asserts are disabled.
51 (void) result;
Thai Duong7689ed62015-03-20 16:50:18 -070052
53 // |prk| is a pseudorandom key (of kSHA256HashLength octets).
54 uint8_t prk[kSHA256HashLength];
55 assert(sizeof(prk) == prk_hmac.DigestLength());
56 result = prk_hmac.Sign(secret, secret_len, prk, sizeof(prk));
57 assert(result);
58
59 // Step 2. Expand: OUTPUT = HKDF-Expand(PRK, info)
60 // https://tools.ietf.org/html/rfc5869#section-2.3
61 const size_t n = (key_bytes_to_generate + kSHA256HashLength - 1) / kSHA256HashLength;
62 assert(n < 256u);
Thai Duong60eebdc2015-03-25 17:20:24 -070063 output_.reset(new uint8_t[n * kSHA256HashLength]);
64 if (!output_.get()) {
65 *error = KM_ERROR_MEMORY_ALLOCATION_FAILED;
66 return;
67 }
Thai Duong7689ed62015-03-20 16:50:18 -070068
Thai Duong7689ed62015-03-20 16:50:18 -070069 uint8_t buf[kSHA256HashLength + info_len + 1];
70 uint8_t digest[kSHA256HashLength];
Thai Duong7689ed62015-03-20 16:50:18 -070071 HmacSha256 hmac;
72 result = hmac.Init(prk, sizeof(prk));
73 assert(result);
74
75 for (size_t i = 1; i <= n; i++) {
Thai Duong60eebdc2015-03-25 17:20:24 -070076 size_t j = 0;
77 if (i != 1) {
78 memcpy(buf, digest, sizeof(digest));
79 j = sizeof(digest);
80 }
Thai Duong7689ed62015-03-20 16:50:18 -070081 memcpy(buf + j, info, info_len);
82 j += info_len;
83 buf[j++] = static_cast<uint8_t>(i);
84 result = hmac.Sign(buf, j, digest, sizeof(digest));
85 assert(result);
Thai Duong60eebdc2015-03-25 17:20:24 -070086 memcpy(output_.get() + (i - 1) * sizeof(digest), digest, sizeof(digest));
Thai Duong7689ed62015-03-20 16:50:18 -070087 }
88
Thai Duong60eebdc2015-03-25 17:20:24 -070089 if (key_bytes_to_generate) {
90 secret_key_len_ = key_bytes_to_generate;
91 secret_key_.reset(new uint8_t[key_bytes_to_generate]);
92 if (!secret_key_.get()) {
93 *error = KM_ERROR_MEMORY_ALLOCATION_FAILED;
94 return;
95 }
96 memcpy(secret_key_.get(), output_.get(), key_bytes_to_generate);
97 }
98 *error = KM_ERROR_OK;
Thai Duong7689ed62015-03-20 16:50:18 -070099}
100
101} // namespace keymaster