class cipher
{
    private $securekey;
    private $iv_size;

    function __construct($textkey)
    {
        $this->iv_size = mcrypt_get_iv_size(
            MCRYPT_RIJNDAEL_128,
            MCRYPT_MODE_CBC
        );
        $this->securekey = hash(
            'sha256',
            $textkey,
            TRUE
        );
    }

    function encrypt($input)
    {
        $iv = mcrypt_create_iv($this->iv_size);
        return base64_encode(
            $iv . mcrypt_encrypt(
                MCRYPT_RIJNDAEL_128,
                $this->securekey,
                $input,
                MCRYPT_MODE_CBC,
                $iv
            )
        );
    }

    function decrypt($input)
    {
        $input = base64_decode($input);
        $iv = substr(
            $input,
            0,
            $this->iv_size
        );
        $cipher = substr(
            $input,
            $this->iv_size
        );
        return trim(
            mcrypt_decrypt(
                MCRYPT_RIJNDAEL_128,
                $this->securekey,
                $cipher,
                MCRYPT_MODE_CBC,
                $iv
            )
        );
    }
}

// Usage
$cipher = new cipher('my-secret-key');
$orignal_text = 'my secret message';
$encrypted_text = $cipher->encrypt($orignal_text);   // store this in db
$decrypted_text = $cipher->decrypt($encrypted_text); // load $encrypted_text from db

// Debug
echo "Orignal Text  : $orignal_text\r\n";
echo "Encrypted Text: $encrypted_text\r\n";
echo "Decrypted Text: $decrypted_text";

Orignal Text  : my secret message
Encrypted Text: Z21ifr5dHEdE9nO8vaDWb9QkjooqCK4UI6D/Ui+fkpmXWwmxloy8hM+7oimtw1wE
Decrypted Text: my secret message