iso18033kdf.cpp revision f7538e0127ec2cb5202b0cbc64ad8305aae6243b 
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 "iso18033kdf.h"
18#include "openssl_utils.h"
19
20#include <algorithm>
21
22#include <openssl/evp.h>
23
24namespace keymaster {
25
26inline size_t min(size_t a, size_t b) {
27    return (a < b) ? a : b;
28}
29
30bool Iso18033Kdf::GenerateKey(const uint8_t* info, size_t info_len, uint8_t* output,
31                              size_t output_len) {
32    if (!is_initialized_ || output == nullptr)
33        return false;
34
35    /* Check whether output length is too long as specified in ISO/IEC 18033-2. */
36    if ((0xFFFFFFFFULL + start_counter_) * digest_size_ < (uint64_t)output_len)
37        return false;
38
39    EVP_MD_CTX ctx;
40    EvpMdCtxCleaner ctxCleaner(&ctx);
41    EVP_MD_CTX_init(&ctx);
42
43    size_t num_blocks = (output_len + digest_size_ - 1) / digest_size_;
44    UniquePtr<uint8_t[]> counter(new uint8_t[4]);
45    UniquePtr<uint8_t[]> digest_result(new uint8_t[digest_size_]);
46    if (counter.get() == nullptr || digest_result.get() == nullptr)
47        return false;
48    for (size_t block = 0; block < num_blocks; block++) {
49        switch (digest_type_) {
50        case KM_DIGEST_SHA1:
51            if (!EVP_DigestInit_ex(&ctx, EVP_sha1(), nullptr /* default digest */))
52                return false;
53            break;
54        case KM_DIGEST_SHA_2_256:
55            if (!EVP_DigestInit_ex(&ctx, EVP_sha256(), nullptr /* default digest */))
56                return false;
57            break;
58        default:
59            return false;
60        }
61
62        if (!EVP_DigestUpdate(&ctx, secret_key_.get(), secret_key_len_) ||
63            !Uint32ToBigEndianByteArray(block + start_counter_, counter.get()) ||
64            !EVP_DigestUpdate(&ctx, counter.get(), 4))
65            return false;
66
67        if (info != nullptr && info_len > 0) {
68            if (!EVP_DigestUpdate(&ctx, info, info_len))
69                return false;
70        }
71
72        /* OpenSSL does not accept size_t parameter. */
73        uint32_t uint32_digest_size_ = digest_size_;
74        if (!EVP_DigestFinal_ex(&ctx, digest_result.get(), &uint32_digest_size_) ||
75            uint32_digest_size_ != digest_size_)
76            return false;
77
78        size_t block_start = digest_size_ * block;
79        size_t block_length = min(digest_size_, output_len - block_start);
80        memcpy(output + block_start, digest_result.get(), block_length);
81    }
82    return true;
83}
84
85}  // namespace keymaster
86