AES Encryption: Handle encryption in the same manor as MySQL's AES_ENCRYPT() and AES_DECRYPT() functions, using openssl instead of the deprecated mcrypt.

helpers.php

<?php

if (!function_exists('mysql_aes_key')) {
    /**
     * Produce a version of the AES key in the same manor as MySQL
     *
     * @param string $key
     * @return string
     * @see https://www.smashingmagazine.com/2012/05/replicating-mysql-aes-encryption-methods-with-php/
     */
    function mysql_aes_key($key)
    {
        $bytes = 16;
        $newKey = str_repeat(chr(0), $bytes);
        $length = strlen($key);
        
        for ($i = 0; $i < $length; $i++) {
            $index = $i % $bytes;
            $newKey[$index] = $newKey[$index] ^ $key[$i];
        }
        
        return $newKey;
    }
}

if (!function_exists('aes_encrypt')) {
    /**
     * Programmatically mimic a MySQL AES_ENCRYPT() action as a way of avoiding unnecessary database calls
     *
     * @param string $decrypted
     * @param string $cypher
     * @param bool $mySqlKey
     * @return string
     */
    function aes_encrypt($decrypted, $cypher = null, $mySqlKey = true)
    {
        static $encryptedValues = [];   //Avoid encrypting a previously encrypted value
        
        if (array_key_exists($decrypted, $encryptedValues)) {
            return $encryptedValues[$decrypted];
        } elseif (in_array($decrypted, $encryptedValues)) {
            return $decrypted;
        }
        
        if (!($salt = getenv('SALT'))) {
            throw new \LogicException('Missing encryption salt.');
        }
        
        $key = $mySqlKey ? mysql_aes_key($salt) : $salt;
        
        $cypher = $cypher ?: 'aes-128-ecb';
        
        $encrypted = openssl_encrypt($decrypted, $cypher, $key, OPENSSL_RAW_DATA);
        
        $encryptedValues[$decrypted] = $encrypted;
        
        return $encrypted;
    }
}

if (!function_exists('aes_decrypt')) {
    /**
     * Programmatically mimic a MySQL AES_DECRYPT() action as a way of avoiding unnecessary database calls
     *
     * @param string $encrypted
     * @param string $cypher
     * @param bool $mySqlKey
     * @return string
     */
    function aes_decrypt($encrypted, $cypher = null, $mySqlKey = true)
    {
        static $decryptedValues = [];   //Avoid decrypting a previously decrypted value
        
        if (array_key_exists($encrypted, $decryptedValues)) {
            return $decryptedValues[$encrypted];
        } elseif (in_array($encrypted, $decryptedValues)) {
            return $encrypted;
        }
        
        if (!($salt = getenv('SALT'))) {
            throw new \LogicException('Missing encryption salt.');
        }
        
        $key = $mySqlKey ? mysql_aes_key($salt) : $salt;
        
        $cypher = $cypher ?: 'aes-128-ecb';
        
        $decrypted = openssl_decrypt($encrypted, $cypher, $key, OPENSSL_RAW_DATA);
        
        $decryptedValues[$encrypted] = $decrypted;
        
        return $decrypted;
    }
}