mcrypt Extension

mcrypt is a PHP extension that provides access to the mcrypt library. It provides a variety of cryptographic algorithms.

mcrypt was deprecated in PHP 7.1 and removed in PHP 7.2. It is recommended to use sodium or openssl instead.

<?php
    $key = pack('H*', "bcb04b7e103a0cd8b54763051cef08bc55abe029fdebae5e1d417e2ffb2a00a3");

    $key_size =  strlen($key);
    echo "Key size: " . $key_size . "\n";

    $plaintext = "This string was AES-256 / CBC / ZeroBytePadding encrypted.";

    # create a random IV to use with CBC encoding
    $iv_size = mcrypt_get_iv_size(MCRYPT_RIJNDAEL_128, MCRYPT_MODE_CBC);
    $iv = mcrypt_create_iv($iv_size, MCRYPT_RAND);

    $ciphertext = mcrypt_encrypt(MCRYPT_RIJNDAEL_128, $key,
                                 $plaintext, MCRYPT_MODE_CBC, $iv);
?>

Documentation

See also ext/sodium, ext/openssl

Related : libsodium, OpenSSL