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<?php
/**
* Copyright 2017 OpenStack Foundation
* 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.
**/
final class Encrypter
{
/**
* The encryption key.
*
* @var string
*/
private $key;
/**
* The algorithm used for encryption.
*
* @var string
*/
private $cipher;
/**
* Encrypter constructor.
* @param $key
* @param string $cipher
*/
public function __construct($key, $cipher = 'AES-128-CBC')
{
$key = (string) $key;
if (strstr($key, 'base64:') !== false) {
$key = base64_decode(substr($key, 7));
}
if (static::supported($key, $cipher)) {
$this->key = $key;
$this->cipher = $cipher;
} else {
throw new RuntimeException('The only supported ciphers are AES-128-CBC and AES-256-CBC with the correct key lengths.');
}
}
/**
* Determine if the given key and cipher combination is valid.
*
* @param string $key
* @param string $cipher
* @return bool
*/
public static function supported($key, $cipher)
{
$length = mb_strlen($key, '8bit');
return ($cipher === 'AES-128-CBC' && $length === 16) || ($cipher === 'AES-256-CBC' && $length === 32);
}
/**
* Encrypt the given value.
*
* @param string $value
* @return string
*
* @throws EncryptException
*/
public function encrypt($value)
{
$iv = random_bytes($this->getIvSize());
$value = \openssl_encrypt(serialize($value), $this->cipher, $this->key, 0, $iv);
if ($value === false) {
throw new EncryptException('Could not encrypt the data.');
}
// Once we have the encrypted value we will go ahead base64_encode the input
// vector and create the MAC for the encrypted value so we can verify its
// authenticity. Then, we'll JSON encode the data in a "payload" array.
$mac = $this->hash($iv = base64_encode($iv), $value);
$json = json_encode(compact('iv', 'value', 'mac'));
if (! is_string($json)) {
throw new EncryptException('Could not encrypt the data.');
}
return base64_encode($json);
}
/**
* Decrypt the given value.
*
* @param string $payload
* @return string
*
* @throws DecryptException
*/
public function decrypt($payload)
{
$payload = $this->getJsonPayload($payload);
$iv = base64_decode($payload['iv']);
$decrypted = \openssl_decrypt($payload['value'], $this->cipher, $this->key, 0, $iv);
if ($decrypted === false) {
throw new DecryptException('Could not decrypt the data.');
}
return unserialize($decrypted);
}
/**
* Get the IV size for the cipher.
*
* @return int
*/
protected function getIvSize()
{
return 16;
}
/**
* Create a MAC for the given value.
*
* @param string $iv
* @param string $value
* @return string
*/
protected function hash($iv, $value)
{
return hash_hmac('sha256', $iv.$value, $this->key);
}
/**
* Get the JSON array from the given payload.
*
* @param string $payload
* @return array
*
* @throws DecryptException
*/
private function getJsonPayload($payload)
{
$payload = json_decode(base64_decode($payload), true);
// If the payload is not valid JSON or does not have the proper keys set we will
// assume it is invalid and bail out of the routine since we will not be able
// to decrypt the given value. We'll also check the MAC for this encryption.
if (! $payload || $this->invalidPayload($payload)) {
throw new DecryptException('The payload is invalid.');
}
if (! $this->validMac($payload)) {
throw new DecryptException('The MAC is invalid.');
}
return $payload;
}
/**
* Verify that the encryption payload is valid.
*
* @param array|mixed $data
* @return bool
*/
private function invalidPayload($data)
{
return ! is_array($data) || ! isset($data['iv']) || ! isset($data['value']) || ! isset($data['mac']);
}
/**
* Determine if the MAC for the given payload is valid.
*
* @param array $payload
* @return bool
*
* @throws \RuntimeException
*/
private function validMac(array $payload)
{
$bytes = random_bytes(16);
$calcMac = hash_hmac('sha256', $this->hash($payload['iv'], $payload['value']), $bytes, true);
return hash_equals(hash_hmac('sha256', $payload['mac'], $bytes, true), $calcMac);
}
}