Encrypting / Decrypting file with Mcrypt

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.