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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 "olm/cipher.h"
#include "olm/crypto.h"
#include "olm/memory.hh"
#include <cstring>
const std::size_t HMAC_KEY_LENGTH = 32;
namespace {
struct DerivedKeys {
_olm_aes256_key aes_key;
std::uint8_t mac_key[HMAC_KEY_LENGTH];
_olm_aes256_iv 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[
AES256_KEY_LENGTH + HMAC_KEY_LENGTH + AES256_IV_LENGTH
];
_olm_crypto_hkdf_sha256(
key, key_length,
nullptr, 0,
kdf_info, kdf_info_length,
derived_secrets, sizeof(derived_secrets)
);
std::uint8_t const * pos = derived_secrets;
pos = olm::load_array(keys.aes_key.key, pos);
pos = olm::load_array(keys.mac_key, pos);
pos = olm::load_array(keys.aes_iv.iv, pos);
olm::unset(derived_secrets);
}
static const std::size_t MAC_LENGTH = 8;
size_t aes_sha_256_cipher_mac_length(const struct _olm_cipher *cipher) {
return MAC_LENGTH;
}
size_t aes_sha_256_cipher_encrypt_ciphertext_length(
const struct _olm_cipher *cipher, size_t plaintext_length
) {
return _olm_crypto_aes_encrypt_cbc_length(plaintext_length);
}
size_t aes_sha_256_cipher_encrypt(
const struct _olm_cipher *cipher,
uint8_t const * key, size_t key_length,
uint8_t const * plaintext, size_t plaintext_length,
uint8_t * ciphertext, size_t ciphertext_length,
uint8_t * output, size_t output_length
) {
auto *c = reinterpret_cast<const _olm_cipher_aes_sha_256 *>(cipher);
if (ciphertext_length
< aes_sha_256_cipher_encrypt_ciphertext_length(cipher, plaintext_length)
|| output_length < MAC_LENGTH) {
return std::size_t(-1);
}
struct DerivedKeys keys;
std::uint8_t mac[SHA256_OUTPUT_LENGTH];
derive_keys(c->kdf_info, c->kdf_info_length, key, key_length, keys);
_olm_crypto_aes_encrypt_cbc(
&keys.aes_key, &keys.aes_iv, plaintext, plaintext_length, ciphertext
);
_olm_crypto_hmac_sha256(
keys.mac_key, HMAC_KEY_LENGTH, output, output_length - MAC_LENGTH, mac
);
std::memcpy(output + output_length - MAC_LENGTH, mac, MAC_LENGTH);
olm::unset(keys);
return output_length;
}
size_t aes_sha_256_cipher_decrypt_max_plaintext_length(
const struct _olm_cipher *cipher,
size_t ciphertext_length
) {
return ciphertext_length;
}
size_t aes_sha_256_cipher_decrypt(
const struct _olm_cipher *cipher,
uint8_t const * key, size_t key_length,
uint8_t const * input, size_t input_length,
uint8_t const * ciphertext, size_t ciphertext_length,
uint8_t * plaintext, size_t max_plaintext_length
) {
if (max_plaintext_length
< aes_sha_256_cipher_decrypt_max_plaintext_length(cipher, ciphertext_length)
|| input_length < MAC_LENGTH) {
return std::size_t(-1);
}
auto *c = reinterpret_cast<const _olm_cipher_aes_sha_256 *>(cipher);
DerivedKeys keys;
std::uint8_t mac[SHA256_OUTPUT_LENGTH];
derive_keys(c->kdf_info, c->kdf_info_length, key, key_length, keys);
_olm_crypto_hmac_sha256(
keys.mac_key, HMAC_KEY_LENGTH, input, input_length - MAC_LENGTH, mac
);
std::uint8_t const * input_mac = input + input_length - MAC_LENGTH;
if (!olm::is_equal(input_mac, mac, MAC_LENGTH)) {
olm::unset(keys);
return std::size_t(-1);
}
std::size_t plaintext_length = _olm_crypto_aes_decrypt_cbc(
&keys.aes_key, &keys.aes_iv, ciphertext, ciphertext_length, plaintext
);
olm::unset(keys);
return plaintext_length;
}
} // namespace
const struct _olm_cipher_ops _olm_cipher_aes_sha_256_ops = {
aes_sha_256_cipher_mac_length,
aes_sha_256_cipher_encrypt_ciphertext_length,
aes_sha_256_cipher_encrypt,
aes_sha_256_cipher_decrypt_max_plaintext_length,
aes_sha_256_cipher_decrypt,
};
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