139 lines
3.9 KiB
C++
139 lines
3.9 KiB
C++
/* Copyright 2015 OpenMarket Ltd
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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 "axolotl/cipher.hh"
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#include "axolotl/crypto.hh"
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#include "axolotl/memory.hh"
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#include <cstring>
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axolotl::Cipher::~Cipher() {
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}
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namespace {
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static const std::size_t SHA256_LENGTH = 32;
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struct DerivedKeys {
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axolotl::Aes256Key aes_key;
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std::uint8_t mac_key[SHA256_LENGTH];
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axolotl::Aes256Iv aes_iv;
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};
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static void derive_keys(
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std::uint8_t const * kdf_info, std::size_t kdf_info_length,
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std::uint8_t const * key, std::size_t key_length,
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DerivedKeys & keys
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) {
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std::uint8_t derived_secrets[80];
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axolotl::hkdf_sha256(
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key, key_length,
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nullptr, 0,
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kdf_info, kdf_info_length,
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derived_secrets, sizeof(derived_secrets)
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);
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std::memcpy(keys.aes_key.key, derived_secrets, 32);
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std::memcpy(keys.mac_key, derived_secrets + 32, 32);
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std::memcpy(keys.aes_iv.iv, derived_secrets + 64, 16);
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axolotl::unset(derived_secrets);
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}
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static const std::size_t MAC_LENGTH = 8;
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} // namespace
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axolotl::CipherAesSha256::CipherAesSha256(
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std::uint8_t const * kdf_info, std::size_t kdf_info_length
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) : kdf_info(kdf_info), kdf_info_length(kdf_info_length) {
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}
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std::size_t axolotl::CipherAesSha256::mac_length() const {
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return MAC_LENGTH;
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}
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std::size_t axolotl::CipherAesSha256::encrypt_ciphertext_length(
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std::size_t plaintext_length
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) const {
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return axolotl::aes_encrypt_cbc_length(plaintext_length);
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}
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std::size_t axolotl::CipherAesSha256::encrypt(
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std::uint8_t const * key, std::size_t key_length,
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std::uint8_t const * plaintext, std::size_t plaintext_length,
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std::uint8_t * ciphertext, std::size_t ciphertext_length,
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std::uint8_t * output, std::size_t output_length
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) const {
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if (encrypt_ciphertext_length(plaintext_length) < ciphertext_length) {
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return std::size_t(-1);
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}
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struct DerivedKeys keys;
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std::uint8_t mac[SHA256_LENGTH];
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derive_keys(kdf_info, kdf_info_length, key, key_length, keys);
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axolotl::aes_encrypt_cbc(
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keys.aes_key, keys.aes_iv, plaintext, plaintext_length, ciphertext
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);
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axolotl::hmac_sha256(
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keys.mac_key, SHA256_LENGTH, output, output_length - MAC_LENGTH, mac
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);
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std::memcpy(output + output_length - MAC_LENGTH, mac, MAC_LENGTH);
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axolotl::unset(keys);
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return output_length;
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}
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std::size_t axolotl::CipherAesSha256::decrypt_max_plaintext_length(
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std::size_t ciphertext_length
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) const {
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return ciphertext_length;
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}
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std::size_t axolotl::CipherAesSha256::decrypt(
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std::uint8_t const * key, std::size_t key_length,
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std::uint8_t const * input, std::size_t input_length,
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std::uint8_t const * ciphertext, std::size_t ciphertext_length,
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std::uint8_t * plaintext, std::size_t max_plaintext_length
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) const {
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DerivedKeys keys;
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std::uint8_t mac[SHA256_LENGTH];
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derive_keys(kdf_info, kdf_info_length, key, key_length, keys);
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axolotl::hmac_sha256(
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keys.mac_key, SHA256_LENGTH, input, input_length - MAC_LENGTH, mac
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);
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std::uint8_t const * input_mac = input + input_length - MAC_LENGTH;
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if (!axolotl::is_equal(input_mac, mac, MAC_LENGTH)) {
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axolotl::unset(keys);
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return std::size_t(-1);
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}
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std::size_t plaintext_length = axolotl::aes_decrypt_cbc(
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keys.aes_key, keys.aes_iv, ciphertext, ciphertext_length, plaintext
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);
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axolotl::unset(keys);
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return plaintext_length;
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}
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