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Convert mcrypt_encrypt to openssl_encrypt in PHP

(Updated on 03 Sep 2024)

mcrypt_encrypt is deprecated

The PHP function mcrypt_encrypt has been DEPRECATED as of PHP 7.1.0 and REMOVED as of PHP 7.2.0.

Warning This function has been DEPRECATED as of PHP 7.1.0 and REMOVED as of PHP 7.2.0. Relying on this function is highly discouraged.

ref. PHP: mcrypt_encrypt - Manual

Use openssl_encrypt instead

If you’re writing code to encrypt/encrypt data in 2015, you should use openssl_encrypt() and openssl_decrypt().

https://www.php.net/manual/en/function.mcrypt-encrypt.php#117667

ref. PHP: openssl_decrypt - Manual

mcrypt_encrypt with MCRYPT_RIJNDAEL_128 and MCRYPT_MODE_CBC

<?php
function pad_zero($data) {
  $block_size = mcrypt_get_block_size(MCRYPT_RIJNDAEL_128, MCRYPT_MODE_CBC);
  $padding = $block_size - (strlen($data) % $block_size);
  return $data . str_repeat("\0", $padding);
}

function my_mcrypt_encrypt($data) {
  $key = pad_zero("my-key");
  $iv = pad_zero('my-iv');
  $encrypted_data = mcrypt_encrypt(MCRYPT_RIJNDAEL_128, $key, $data, MCRYPT_MODE_CBC, $iv);
  return base64_encode($encrypted_data);
}

function my_mcrypt_decrypt($encrypted_data) {
  $key = pad_zero("my-key");
  $iv = pad_zero('my-iv');
  $encrypted_data = base64_decode($encrypted_data);
  $decrypted_data = mcrypt_decrypt(MCRYPT_RIJNDAEL_128, $key, $encrypted_data, MCRYPT_MODE_CBC, $iv);
  return rtrim($decrypted_data, "\0");
}

echo my_mcrypt_encrypt("test"); //YcBFq1jPeN7rKB1WWLeZOA==
echo my_mcrypt_decrypt("YcBFq1jPeN7rKB1WWLeZOA=="); //test

openssl_encrypt with aes-128-cbc

<?php
function pad_zero($data) {
  $block_size = openssl_cipher_iv_length("aes-128-cbc");
  $padding = $block_size - (strlen($data) % $block_size);
  return $data . str_repeat("\0", $padding);
}

function my_openssl_encrypt($data) {
  $key = pad_zero("my-key");
  $iv = pad_zero('my-iv');
  $method = "aes-128-cbc";
  $encrypted_data = openssl_encrypt(pad_zero($data), $method, $key, OPENSSL_RAW_DATA|OPENSSL_ZERO_PADDING , $iv);
  return base64_encode($encrypted_data);
}

function my_openssl_decrypt($encrypted_data) {
  $key = pad_zero("my-key");
  $iv = pad_zero('my-iv');
  $method = "aes-128-cbc";
  $encrypted_data = base64_decode($encrypted_data);
  $decrypted_data = openssl_decrypt($encrypted_data, $method, $key, OPENSSL_RAW_DATA | OPENSSL_ZERO_PADDING, $iv);
  return rtrim($decrypted_data, "\0"); // Remove padding
}

echo my_openssl_encrypt("test"); //YcBFq1jPeN7rKB1WWLeZOA==
echo my_openssl_decrypt("YcBFq1jPeN7rKB1WWLeZOA=="); //test

AES vs RIJNDAEL

Algorithm Key Length (bytes) IV Length (bytes) Block Length (bytes)
AES-128 16 16 16
AES-192 24 16 16
AES-256 32 16 16
Rijndael-128 16/24/32 16 16
Rijndael-192 16/24/32 24 24
Rijndael-256 16/24/32 32 32

ref. [Japanese (My Japanese Blog)] 2024-08-27 AES vs Rijndael | TTIL

options

Available options are:

  1. OPENSSL_RAW_DATA (int)
  2. OPENSSL_DONT_ZERO_PAD_KEY (int)
  3. OPENSSL_ZERO_PADDING (int)
  4. OPENSSL_ENCODING_SMIME (int)
  5. OPENSSL_ENCODING_DER (int)
  6. OPENSSL_ENCODING_PEM (int)

ref. PHP: Other Constants - Manual

You can specify bitwise OR (|) of the flags.

Function Tests

The results are the same.

php > echo my_mcrypt_encrypt("a");
hxHEroQFXNwHMXeCaO8Oyw==
php > echo my_openssl_encrypt("a");
hxHEroQFXNwHMXeCaO8Oyw==

php > echo my_mcrypt_encrypt("my encription string");
xYsMYUYqNXe7MKJWKUHseEp/SShKk48idzhTC43cYK4=
php > echo my_openssl_encrypt("my encription string");
xYsMYUYqNXe7MKJWKUHseEp/SShKk48idzhTC43cYK4=

References
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