<?php

class LaravelCookieDecrypter {

    /**
     * The encryption key.
     *
     * @var string
     */
    protected $key = 'YOUR LARAVEL .ENV APP KEY';

    /**
     * The algorithm used for encryption.
     *
     * @var string
     */
    protected $cipher = MCRYPT_RIJNDAEL_128;

    /**
     * The mode used for encryption.
     *
     * @var string
     */
    protected $mode = MCRYPT_MODE_CBC;

    /**
     * The block size of the cipher.
     *
     * @var int
     */
    protected $block = 16;

    protected $stringUtils;

    /**
     * LaravelCookieDecrypter constructor.
     */
    public function __construct()
    {
        require_once('SecureRandom.php');
        require_once('StringUtils.php');
    }


    public function decrypt($payload)
    {
        $payload = $this->getJsonPayload($payload);

        // We'll go ahead and remove the PKCS7 padding from the encrypted value before
        // we decrypt it. Once we have the de-padded value, we will grab the vector
        // and decrypt the data, passing back the unserialized from of the value.
        $value = base64_decode($payload['value']);

        $iv = base64_decode($payload['iv']);

        return unserialize($this->stripPadding($this->mcryptDecrypt($value, $iv)));
    }


    protected function getJsonPayload($payload)
    {
        $payload = json_decode(base64_decode($payload), true);

        // If the payload is not valid JSON or does not have the proper keys set we will
        // assume it is invalid and bail out of the routine since we will not be able
        // to decrypt the given value. We'll also check the MAC for this encryption.
        if ( ! $payload || $this->invalidPayload($payload))
        {
            var_dump('Invalid data.');
        }

        if ( ! $this->validMac($payload))
        {
            var_dump('MAC is invalid.');
        }

        return $payload;
    }


    protected function validMac(array $payload)
    {
        $bytes = (new SecureRandom)->nextBytes(16);

        $calcMac = hash_hmac('sha256', $this->hash($payload['iv'], $payload['value']), $bytes, true);

        return StringUtils::equals(hash_hmac('sha256', $payload['mac'], $bytes, true), $calcMac);
    }

    protected function stripPadding($value)
    {
        $pad = ord($value[($len = strlen($value)) - 1]);

        return $this->paddingIsValid($pad, $value) ? substr($value, 0, $len - $pad) : $value;
    }


    protected function mcryptDecrypt($value, $iv)
    {
        try
        {
            return mcrypt_decrypt($this->cipher, $this->key, $value, $this->mode, $iv);
        }
        catch (Exception $e)
        {
            var_dump($e->getMessage());
            die;
        }
    }


    protected function invalidPayload($data)
    {
        return ! is_array($data) || ! isset($data['iv']) || ! isset($data['value']) || ! isset($data['mac']);
    }

    protected function paddingIsValid($pad, $value)
    {
        $beforePad = strlen($value) - $pad;

        return substr($value, $beforePad) == str_repeat(substr($value, -1), $pad);
    }


    protected function hash($iv, $value)
    {
        return hash_hmac('sha256', $iv.$value, $this->key);
    }


}