Encrypting / Decrypting file with Mcrypt
While Johns answer is good, using base64 encoding just to fix the binary safety issue is overkill and will make your encrypted files 33% larger than the original. Here is my PHP Implementation of the AES Crypt file format which solves all the above issues transparently.
https://github.com/philios33/PHP-AES-File-Encryption
It is binary safe and includes authenticated encryption. Since it uses the open source aes crypt file format (.aes) it is fully compatible with other .aes software.
https://www.aescrypt.com/
The interface is pretty simple whether you are encrypting or decrypting. You just give it a source file and password.
You should not be using Mcrypt to encrypt/decrypt data. As shown in your question, and in the accepted answer, the data is not authenticated, which means it will fall victim to chosen ciphertext attacks.
Further, a great deal of effort has been done to make sure that developers put together cryptographic primitives correctly. As such, instead of Mcrypt, you should be using libsodium for your PHP projects. libsodium is a fork of NaCl. NaCl/libsodium is written to remove a lot of the cryptographic pitfalls that developers find themselves in, such as timing attacks with verification of MAC tags.
Mcrypt is deprecated in PHP 7.1, and libsodim is the preferred way to handle cryptography in PHP.
Using libsodium in your PHP project is easy, and secure. Scott Arciszewski has written an extensive ebook on using libsodium with PHP at https://paragonie.com/book/pecl-libsodium. It's worth the read for anyone doing PHP cryptography.
CakePHP has a pretty good implementation of rijndael. I'm not posting code directly here because not sure the legal ramifications.
Here are the api docs for the Security::rijndael() method.
If encoding a file, you will want to base64_encode() before calling this method with 'encrypt', and base64_decode() after calling this method with 'decrypt'
Since mcrypt is abandonware and no longer recommended to be used, here's an example using openssl.
class AES256Encryption
{
public const BLOCK_SIZE = 8;
public const IV_LENGTH = 16;
public const CIPHER = 'AES256';
public static function generateIv(bool $allowLessSecure = false): string
{
$success = false;
$random = openssl_random_pseudo_bytes(openssl_cipher_iv_length(static::CIPHER));
if (!$success) {
if (function_exists('sodium_randombytes_random16')) {
$random = sodium_randombytes_random16();
} else {
try {
$random = random_bytes(static::IV_LENGTH);
}
catch (Exception $e) {
if ($allowLessSecure) {
$permitted_chars = implode(
'',
array_merge(
range('A', 'z'),
range(0, 9),
str_split('~!@#$%&*()-=+{};:"<>,.?/\'')
)
);
$random = '';
for ($i = 0; $i < static::IV_LENGTH; $i++) {
$random .= $permitted_chars[mt_rand(0, (static::IV_LENGTH) - 1)];
}
}
else {
throw new RuntimeException('Unable to generate initialization vector (IV)');
}
}
}
}
return $random;
}
protected static function getPaddedText(string $plainText): string
{
$stringLength = strlen($plainText);
if ($stringLength % static::BLOCK_SIZE) {
$plainText = str_pad($plainText, $stringLength + static::BLOCK_SIZE - $stringLength % static::BLOCK_SIZE, "\0");
}
return $plainText;
}
public static function encrypt(string $plainText, string $key, string $iv): string
{
$plainText = static::getPaddedText($plainText);
return base64_encode(openssl_encrypt($plainText, static::CIPHER, $key, OPENSSL_RAW_DATA, $iv));
}
public static function decrypt(string $encryptedText, string $key, string $iv): string
{
return openssl_decrypt(base64_decode($encryptedText), static::CIPHER, $key, OPENSSL_RAW_DATA, $iv);
}
}
$text = '8SViI0Gz4r-p7A15YxkwjOBFuW*@NTtbm{U]D&E=~6yLM+adX'P;h3$,KJ%/eo>}<Rs:2#gZ.9fqn"Cv_^[(H\c!)?`Ql';
$key = 'secretkey';
$iv = AES256Encryption::generateIv();
$encryptedText = AES256Encryption::encrypt($text, $key, $iv);
$decryptedText = AES256Encryption::decrypt($encryptedText, $key, $iv);
printf('Original Text: %s%s', $text, PHP_EOL);
printf('Encrypted: %s%s', $encryptedText, PHP_EOL);
printf('Decrypted: %s%s', $decryptedText, PHP_EOL);
Output:
// Long string with lots of different characters
Original Text: 8SViI0Gz4r-p7A15YxkwjOBFuW*@NTtbm{U]D&E=~6yLM+adX'P;h3$,KJ%/eo>}<Rs:2#gZ.9fqn"Cv_^[(H\c!)?`Ql
Encrypted : rsiF4PMCMyvAp+CTuJrxJYGoV4BSy8Fy+q+FL8m64+Mt5V3o0HS0elRkWXsy+//hPjzNhjmVktxVvMY55Negt4DyLcf2QpH05wUX+adJDe634J/9fWd+nlEFoDutXuhY+/Kep9zUZFDmLmszJaBHWQ==
Decrypted : 8SViI0Gz4r-p7A15YxkwjOBFuW*@NTtbm{U]D&E=~6yLM+adX'P;h3$,KJ%/eo>}<Rs:2#gZ.9fqn"Cv_^[(H\c!)?`Ql
Old Answer
Try this PHP5 class for encryption using mcrypt. In this case it's using AES encryption. You'll want to change the key for each site you use it on. If you don't use it at least it may guide you on writing your own version of it.
<?php
class Encryption
{
const CIPHER = MCRYPT_RIJNDAEL_128; // Rijndael-128 is AES
const MODE = MCRYPT_MODE_CBC;
/* Cryptographic key of length 16, 24 or 32. NOT a password! */
private $key;
public function __construct($key) {
$this->key = $key;
}
public function encrypt($plaintext) {
$ivSize = mcrypt_get_iv_size(self::CIPHER, self::MODE);
$iv = mcrypt_create_iv($ivSize, MCRYPT_DEV_URANDOM);
$ciphertext = mcrypt_encrypt(self::CIPHER, $this->key, $plaintext, self::MODE, $iv);
return base64_encode($iv.$ciphertext);
}
public function decrypt($ciphertext) {
$ciphertext = base64_decode($ciphertext);
$ivSize = mcrypt_get_iv_size(self::CIPHER, self::MODE);
if (strlen($ciphertext) < $ivSize) {
throw new Exception('Missing initialization vector');
}
$iv = substr($ciphertext, 0, $ivSize);
$ciphertext = substr($ciphertext, $ivSize);
$plaintext = mcrypt_decrypt(self::CIPHER, $this->key, $ciphertext, self::MODE, $iv);
return rtrim($plaintext, "\0");
}
}
Usage:
$key = /* CRYPTOGRAPHIC!!! key */;
$crypt = new Encryption($key);
$encrypted_string = $crypt->encrypt('this is a test');
$decrypted_string = $crypt->decrypt($encrypted_string); // this is a test
Notes:
- This class is not safe for use with binary data (which may end in NUL bytes)
- This class does not provide authenticated encryption.