84 lines
3.3 KiB
C++
84 lines
3.3 KiB
C++
/*
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* Copyright 2015 The Android Open Source Project
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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#include <keymaster/km_openssl/hkdf.h>
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#include <keymaster/android_keymaster_utils.h>
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#include <keymaster/km_openssl/hmac.h>
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namespace keymaster {
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bool Rfc5869Sha256Kdf::GenerateKey(const uint8_t* info, size_t info_len, uint8_t* output,
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size_t output_len) {
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if (!is_initialized_ || output == nullptr) return false;
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/**
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* Step 1. Extract: PRK = HMAC-SHA256(actual_salt, secret)
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* https://tools.ietf.org/html/rfc5869#section-2.2
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*/
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HmacSha256 prk_hmac;
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bool result;
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if (salt_.get() != nullptr && salt_len_ > 0) {
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result = prk_hmac.Init(salt_.get(), salt_len_);
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} else {
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UniquePtr<uint8_t[]> zeros(new (std::nothrow) uint8_t[digest_size_]);
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if (zeros.get() == nullptr) return false;
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/* If salt is not given, digest size of zeros are used. */
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memset(zeros.get(), 0, digest_size_);
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result = prk_hmac.Init(zeros.get(), digest_size_);
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}
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if (!result) return false;
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UniquePtr<uint8_t[]> pseudo_random_key(new (std::nothrow) uint8_t[digest_size_]);
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if (pseudo_random_key.get() == nullptr || digest_size_ != prk_hmac.DigestLength()) return false;
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result =
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prk_hmac.Sign(secret_key_.get(), secret_key_len_, pseudo_random_key.get(), digest_size_);
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if (!result) return false;
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/**
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* Step 2. Expand: OUTPUT = HKDF-Expand(PRK, info)
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* https://tools.ietf.org/html/rfc5869#section-2.3
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*/
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const size_t num_blocks = (output_len + digest_size_ - 1) / digest_size_;
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if (num_blocks >= 256u) return false;
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UniquePtr<uint8_t[]> buf(new (std::nothrow) uint8_t[digest_size_ + info_len + 1]);
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UniquePtr<uint8_t[]> digest(new (std::nothrow) uint8_t[digest_size_]);
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if (buf.get() == nullptr || digest.get() == nullptr) return false;
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HmacSha256 hmac;
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result = hmac.Init(pseudo_random_key.get(), digest_size_);
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if (!result) return false;
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for (size_t i = 0; i < num_blocks; i++) {
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size_t block_input_len = 0;
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if (i != 0) {
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memcpy(buf.get(), digest.get(), digest_size_);
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block_input_len = digest_size_;
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}
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if (info != nullptr && info_len > 0) memcpy(buf.get() + block_input_len, info, info_len);
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block_input_len += info_len;
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*(buf.get() + block_input_len++) = static_cast<uint8_t>(i + 1);
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result = hmac.Sign(buf.get(), block_input_len, digest.get(), digest_size_);
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if (!result) return false;
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size_t block_output_len = digest_size_ < output_len - i * digest_size_
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? digest_size_
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: output_len - i * digest_size_;
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memcpy(output + i * digest_size_, digest.get(), block_output_len);
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}
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return true;
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}
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} // namespace keymaster
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