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/* Copyright 2015 OpenMarket Ltd
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#include "axolotl/cipher.hh"
#include "axolotl/crypto.hh"
#include "axolotl/memory.hh"
#include <cstring>
axolotl::Cipher::~Cipher() {
}
namespace {
static const std::size_t SHA256_LENGTH = 32;
struct DerivedKeys {
axolotl::Aes256Key aes_key;
std::uint8_t mac_key[SHA256_LENGTH];
axolotl::Aes256Iv aes_iv;
};
static void derive_keys(
std::uint8_t const * kdf_info, std::size_t kdf_info_length,
std::uint8_t const * key, std::size_t key_length,
DerivedKeys & keys
) {
std::uint8_t derived_secrets[80];
axolotl::hkdf_sha256(
key, key_length,
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kdf_info, kdf_info_length,
derived_secrets, sizeof(derived_secrets)
);
std::memcpy(keys.aes_key.key, derived_secrets, 32);
std::memcpy(keys.mac_key, derived_secrets + 32, 32);
std::memcpy(keys.aes_iv.iv, derived_secrets + 64, 16);
axolotl::unset(derived_secrets);
}
static const std::size_t MAC_LENGTH = 8;
} // namespace
axolotl::CipherAesSha256::CipherAesSha256(
std::uint8_t const * kdf_info, std::size_t kdf_info_length
) : kdf_info(kdf_info), kdf_info_length(kdf_info_length) {
}
std::size_t axolotl::CipherAesSha256::mac_length() const {
return MAC_LENGTH;
}
std::size_t axolotl::CipherAesSha256::encrypt_ciphertext_length(
std::size_t plaintext_length
) const {
return axolotl::aes_encrypt_cbc_length(plaintext_length);
}
std::size_t axolotl::CipherAesSha256::encrypt(
std::uint8_t const * key, std::size_t key_length,
std::uint8_t const * plaintext, std::size_t plaintext_length,
std::uint8_t * ciphertext, std::size_t ciphertext_length,
std::uint8_t * output, std::size_t output_length
) const {
if (encrypt_ciphertext_length(plaintext_length) < ciphertext_length) {
return std::size_t(-1);
}
struct DerivedKeys keys;
std::uint8_t mac[SHA256_LENGTH];
derive_keys(kdf_info, kdf_info_length, key, key_length, keys);
axolotl::aes_encrypt_cbc(
keys.aes_key, keys.aes_iv, plaintext, plaintext_length, ciphertext
);
axolotl::hmac_sha256(
keys.mac_key, SHA256_LENGTH, output, output_length - MAC_LENGTH, mac
);
std::memcpy(output + output_length - MAC_LENGTH, mac, MAC_LENGTH);
axolotl::unset(keys);
return output_length;
}
std::size_t axolotl::CipherAesSha256::decrypt_max_plaintext_length(
std::size_t ciphertext_length
) const {
return ciphertext_length;
}
std::size_t axolotl::CipherAesSha256::decrypt(
std::uint8_t const * key, std::size_t key_length,
std::uint8_t const * input, std::size_t input_length,
std::uint8_t const * ciphertext, std::size_t ciphertext_length,
std::uint8_t * plaintext, std::size_t max_plaintext_length
) const {
DerivedKeys keys;
std::uint8_t mac[SHA256_LENGTH];
derive_keys(kdf_info, kdf_info_length, key, key_length, keys);
axolotl::hmac_sha256(
keys.mac_key, SHA256_LENGTH, input, input_length - MAC_LENGTH, mac
);
std::uint8_t const * input_mac = input + input_length - MAC_LENGTH;
if (!axolotl::is_equal(input_mac, mac, MAC_LENGTH)) {
axolotl::unset(keys);
return std::size_t(-1);
}
std::size_t plaintext_length = axolotl::aes_decrypt_cbc(
keys.aes_key, keys.aes_iv, ciphertext, ciphertext_length, plaintext
);
axolotl::unset(keys);
return plaintext_length;
}