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 "hkdf.h"
18
19#include <new>
20
21#include <keymaster/android_keymaster_utils.h>
22
23#include "hmac.h"
24
25namespace keymaster {
26
27bool Rfc5869Sha256Kdf::GenerateKey(const uint8_t* info, size_t info_len, uint8_t* output,
28                                   size_t output_len) {
29    if (!is_initialized_ || output == nullptr)
30        return false;
31    /**
32     * Step 1. Extract: PRK = HMAC-SHA256(actual_salt, secret)
33     * https://tools.ietf.org/html/rfc5869#section-2.2
34     */
35    HmacSha256 prk_hmac;
36    bool result;
37    if (salt_.get() != nullptr && salt_len_ > 0) {
38        result = prk_hmac.Init(salt_.get(), salt_len_);
39    } else {
40        UniquePtr<uint8_t[]> zeros(new uint8_t[digest_size_]);
41        if (zeros.get() == nullptr)
42            return false;
43        /* If salt is not given, digest size of zeros are used. */
44        memset(zeros.get(), 0, digest_size_);
45        result = prk_hmac.Init(zeros.get(), digest_size_);
46    }
47    if (!result)
48        return false;
49
50    UniquePtr<uint8_t[]> pseudo_random_key(new uint8_t[digest_size_]);
51    if (pseudo_random_key.get() == nullptr || digest_size_ != prk_hmac.DigestLength())
52        return false;
53    result =
54        prk_hmac.Sign(secret_key_.get(), secret_key_len_, pseudo_random_key.get(), digest_size_);
55    if (!result)
56        return false;
57
58    /**
59     * Step 2. Expand: OUTPUT = HKDF-Expand(PRK, info)
60     * https://tools.ietf.org/html/rfc5869#section-2.3
61     */
62    const size_t num_blocks = (output_len + digest_size_ - 1) / digest_size_;
63    if (num_blocks >= 256u)
64        return false;
65
66    UniquePtr<uint8_t[]> buf(new uint8_t[digest_size_ + info_len + 1]);
67    UniquePtr<uint8_t[]> digest(new uint8_t[digest_size_]);
68    if (buf.get() == nullptr || digest.get() == nullptr)
69        return false;
70    HmacSha256 hmac;
71    result = hmac.Init(pseudo_random_key.get(), digest_size_);
72    if (!result)
73        return false;
74
75    for (size_t i = 0; i < num_blocks; i++) {
76        size_t block_input_len = 0;
77        if (i != 0) {
78            memcpy(buf.get(), digest.get(), digest_size_);
79            block_input_len = digest_size_;
80        }
81        if (info != nullptr && info_len > 0)
82            memcpy(buf.get() + block_input_len, info, info_len);
83        block_input_len += info_len;
84        *(buf.get() + block_input_len++) = static_cast<uint8_t>(i + 1);
85        result = hmac.Sign(buf.get(), block_input_len, digest.get(), digest_size_);
86        if (!result)
87            return false;
88        size_t block_output_len = digest_size_ < output_len - i * digest_size_
89                                      ? digest_size_
90                                      : output_len - i * digest_size_;
91        memcpy(output + i * digest_size_, digest.get(), block_output_len);
92    }
93    return true;
94}
95
96}  // namespace keymaster
97