下面是一个强加密方法的 PHP 类实现:

/**
* A class to handle secure encryption and decryption of arbitrary data
*
* Note that this is not just straight encryption.  It also has a few other
*  features in it to make the encrypted data far more secure.  Note that any
*  other implementations used to decrypt data will have to do the same exact
*  operations.
*
* Security Benefits:
*
* - Uses Key stretching
* - Hides the Initialization Vector
* - Does HMAC verification of source data
*
*/
class Encryption {


/**
* @var string $cipher The mcrypt cipher to use for this instance
*/
protected $cipher = '';


/**
* @var int $mode The mcrypt cipher mode to use
*/
protected $mode = '';


/**
* @var int $rounds The number of rounds to feed into PBKDF2 for key generation
*/
protected $rounds = 100;


/**
* Constructor!
*
* @param string $cipher The MCRYPT_* cypher to use for this instance
* @param int    $mode   The MCRYPT_MODE_* mode to use for this instance
* @param int    $rounds The number of PBKDF2 rounds to do on the key
*/
public function __construct($cipher, $mode, $rounds = 100) {
$this->cipher = $cipher;
$this->mode = $mode;
$this->rounds = (int) $rounds;
}


/**
* Decrypt the data with the provided key
*
* @param string $data The encrypted datat to decrypt
* @param string $key  The key to use for decryption
*
* @returns string|false The returned string if decryption is successful
*                           false if it is not
*/
public function decrypt($data, $key) {
$salt = substr($data, 0, 128);
$enc = substr($data, 128, -64);
$mac = substr($data, -64);


list ($cipherKey, $macKey, $iv) = $this->getKeys($salt, $key);


if (!hash_equals(hash_hmac('sha512', $enc, $macKey, true), $mac)) {
return false;
}


$dec = mcrypt_decrypt($this->cipher, $cipherKey, $enc, $this->mode, $iv);


$data = $this->unpad($dec);


return $data;
}


/**
* Encrypt the supplied data using the supplied key
*
* @param string $data The data to encrypt
* @param string $key  The key to encrypt with
*
* @returns string The encrypted data
*/
public function encrypt($data, $key) {
$salt = mcrypt_create_iv(128, MCRYPT_DEV_URANDOM);
list ($cipherKey, $macKey, $iv) = $this->getKeys($salt, $key);


$data = $this->pad($data);


$enc = mcrypt_encrypt($this->cipher, $cipherKey, $data, $this->mode, $iv);


$mac = hash_hmac('sha512', $enc, $macKey, true);
return $salt . $enc . $mac;
}


/**
* Generates a set of keys given a random salt and a master key
*
* @param string $salt A random string to change the keys each encryption
* @param string $key  The supplied key to encrypt with
*
* @returns array An array of keys (a cipher key, a mac key, and a IV)
*/
protected function getKeys($salt, $key) {
$ivSize = mcrypt_get_iv_size($this->cipher, $this->mode);
$keySize = mcrypt_get_key_size($this->cipher, $this->mode);
$length = 2 * $keySize + $ivSize;


$key = $this->pbkdf2('sha512', $key, $salt, $this->rounds, $length);


$cipherKey = substr($key, 0, $keySize);
$macKey = substr($key, $keySize, $keySize);
$iv = substr($key, 2 * $keySize);
return array($cipherKey, $macKey, $iv);
}


/**
* Stretch the key using the PBKDF2 algorithm
*
* @see http://en.wikipedia.org/wiki/PBKDF2
*
* @param string $algo   The algorithm to use
* @param string $key    The key to stretch
* @param string $salt   A random salt
* @param int    $rounds The number of rounds to derive
* @param int    $length The length of the output key
*
* @returns string The derived key.
*/
protected function pbkdf2($algo, $key, $salt, $rounds, $length) {
$size   = strlen(hash($algo, '', true));
$len    = ceil($length / $size);
$result = '';
for ($i = 1; $i <= $len; $i++) {
$tmp = hash_hmac($algo, $salt . pack('N', $i), $key, true);
$res = $tmp;
for ($j = 1; $j < $rounds; $j++) {
$tmp  = hash_hmac($algo, $tmp, $key, true);
$res ^= $tmp;
}
$result .= $res;
}
return substr($result, 0, $length);
}


protected function pad($data) {
$length = mcrypt_get_block_size($this->cipher, $this->mode);
$padAmount = $length - strlen($data) % $length;
if ($padAmount == 0) {
$padAmount = $length;
}
return $data . str_repeat(chr($padAmount), $padAmount);
}


protected function unpad($data) {
$length = mcrypt_get_block_size($this->cipher, $this->mode);
$last = ord($data[strlen($data) - 1]);
if ($last > $length) return false;
if (substr($data, -1 * $last) !== str_repeat(chr($last), $last)) {
return false;
}
return substr($data, 0, -1 * $last);
}
}

注意，我正在使用 PHP 5.6中添加的一个函数: hash_equals。如果低于5.6，可以使用这个替代函数，它使用 双重 HMAC 验证实现一个 定时安全比较函数:

function hash_equals($a, $b) {
$key = mcrypt_create_iv(128, MCRYPT_DEV_URANDOM);
return hash_hmac('sha512', $a, $key) === hash_hmac('sha512', $b, $key);
}

用法:

$e = new Encryption(MCRYPT_BLOWFISH, MCRYPT_MODE_CBC);
$encryptedData = $e->encrypt($data, $key);

然后，解密:

$e2 = new Encryption(MCRYPT_BLOWFISH, MCRYPT_MODE_CBC);
$data = $e2->decrypt($encryptedData, $key);

注意，我第二次使用 $e2显示不同的实例仍然会正确地解密数据。

现在，它是如何工作的/为什么使用它而不是另一种解决方案:

1. 钥匙

• 不直接使用密钥，而是通过标准的 PBKDF2派生来拉伸密钥。

• 用于加密的密钥对于每个加密的文本块都是唯一的。因此，提供的密钥成为“主密钥”。因此，这个类提供了密码和认证密钥的密钥轮换。

• 重要提示 ，$rounds参数配置为具有足够强度的真随机密钥(至少128位加密安全随机密钥)。如果您要使用密码，或非随机密钥(或随机性小于128位的 CS 随机) ，则 必须的增加此参数。我建议至少设置10000个密码(你能负担得起的越多越好，但它会增加运行时) ..。

2. 资料完整性

• 更新的版本使用 ENCRYPT-THEN-MAC，这是确保加密数据真实性的更好方法。

3. 加密:

• 它使用 mcrypt 实际执行加密。我建议使用 MCRYPT_BLOWFISH或 MCRYPT_RIJNDAEL_128密码和 MCRYPT_MODE_CBC的模式。它足够强大，而且仍然相当快(在我的机器上，加密和解密周期大约需要1/2秒)。

现在，对于第一个列表中的第3点，它会给你一个像这样的函数:

function makeKey($userKey, $serverKey, $userSuppliedKey) {
$key = hash_hmac('sha512', $userKey, $serverKey);
$key = hash_hmac('sha512', $key, $userSuppliedKey);
return $key;
}

你可以在 makeKey()函数中拉伸它，但是因为它将在稍后被拉伸，所以这样做并没有什么意义。

就存储大小而言，它取决于纯文本。河豚使用8字节的块大小，因此您将有:

• Salt 为16个字节
• Hmac 是64字节
• 数据长度
• 填充，使数据长度% 8 = = 0

因此，对于一个16个字符的数据源，需要对16个字符的数据进行加密。这意味着由于填充，实际加密的数据大小是16字节。然后添加16个字节的 salt 和64个字节的 hmac，总存储大小为96个字节。所以顶多有80个字符的开销，顶多有87个字符的开销..。