<?php
/**
 * Joomla! Content Management System
 *
 * @copyright  (C) 2016 Open Source Matters, Inc. <https://www.joomla.org>
 * @license    GNU General Public License version 2 or later; see LICENSE.txt
 */

namespace Joomla\CMS\Encrypt\AES;

use Joomla\CMS\Encrypt\Randval;

\defined('JPATH_PLATFORM') or die;

/**
 * OpenSSL encryption class
 *
 * @since   4.0.0
 */
class OpenSSL extends AbstractAES implements AesInterface
{
	/**
	 * The OpenSSL options for encryption / decryption
	 *
	 * @var  integer
	 */
	protected $openSSLOptions = 0;

	/**
	 * The encryption method to use
	 *
	 * @var  string
	 */
	protected $method = 'aes-128-cbc';

	/**
	 * Constructor for this class
	 */
	public function __construct()
	{
		$this->openSSLOptions = OPENSSL_RAW_DATA | OPENSSL_ZERO_PADDING;
	}

	/**
	 * Sets the AES encryption mode.
	 *
	 * WARNING: The strength is deprecated as it has a different effect in MCrypt and OpenSSL. MCrypt was abandoned in
	 * 2003 before the Rijndael-128 algorithm was officially the Advanced Encryption Standard (AES). MCrypt also offered
	 * Rijndael-192 and Rijndael-256 algorithms with different block sizes. These are NOT used in AES. OpenSSL, however,
	 * implements AES correctly. It always uses a 128-bit (16 byte) block. The 192 and 256 bit strengths refer to the
	 * key size, not the block size. Therefore using different strengths in MCrypt and OpenSSL will result in different
	 * and incompatible ciphertexts.
	 *
	 * TL;DR: Always use $strength = 128!
	 *
	 * @param   string  $mode      Choose between CBC (recommended) or ECB
	 * @param   int     $strength  Bit strength of the key (128, 192 or 256 bits). DEPRECATED. READ NOTES ABOVE.
	 *
	 * @return  mixed
	 */
	public function setEncryptionMode($mode = 'cbc', $strength = 128)
	{
		static $availableAlgorithms = null;
		static $defaultAlgo = 'aes-128-cbc';

		if (!\is_array($availableAlgorithms))
		{
			$availableAlgorithms = openssl_get_cipher_methods();

			foreach (array('aes-256-cbc', 'aes-256-ecb', 'aes-192-cbc',
				'aes-192-ecb', 'aes-128-cbc', 'aes-128-ecb') as $algo
			)
			{
				if (\in_array($algo, $availableAlgorithms))
				{
					$defaultAlgo = $algo;
					break;
				}
			}
		}

		$strength = (int) $strength;
		$mode     = strtolower($mode);

		if (!\in_array($strength, array(128, 192, 256)))
		{
			$strength = 256;
		}

		if (!\in_array($mode, array('cbc', 'ebc')))
		{
			$mode = 'cbc';
		}

		$algo = 'aes-' . $strength . '-' . $mode;

		if (!\in_array($algo, $availableAlgorithms))
		{
			$algo = $defaultAlgo;
		}

		$this->method = $algo;
	}

	/**
	 * Encrypts a string. Returns the raw binary ciphertext.
	 *
	 * WARNING: The plaintext is zero-padded to the algorithm's block size. You are advised to store the size of the
	 * plaintext and trim the string to that length upon decryption.
	 *
	 * @param   string       $plainText  The plaintext to encrypt
	 * @param   string       $key        The raw binary key (will be zero-padded or chopped if its size is different than the block size)
	 * @param   null|string  $iv         The initialization vector (for CBC mode algorithms)
	 *
	 * @return  string  The raw encrypted binary string.
	 */
	public function encrypt($plainText, $key, $iv = null)
	{
		$iv_size = $this->getBlockSize();
		$key     = $this->resizeKey($key, $iv_size);
		$iv      = $this->resizeKey($iv, $iv_size);

		if (empty($iv))
		{
			$randVal   = new Randval;
			$iv        = $randVal->generate($iv_size);
		}

		$plainText .= $this->getZeroPadding($plainText, $iv_size);
		$cipherText = openssl_encrypt($plainText, $this->method, $key, $this->openSSLOptions, $iv);
		$cipherText = $iv . $cipherText;

		return $cipherText;
	}

	/**
	 * Decrypts a string. Returns the raw binary plaintext.
	 *
	 * $ciphertext MUST start with the IV followed by the ciphertext, even for EBC data (the first block of data is
	 * dropped in EBC mode since there is no concept of IV in EBC).
	 *
	 * WARNING: The returned plaintext is zero-padded to the algorithm's block size during encryption. You are advised
	 * to trim the string to the original plaintext's length upon decryption. While rtrim($decrypted, "\0") sounds
	 * appealing it's NOT the correct approach for binary data (zero bytes may actually be part of your plaintext, not
	 * just padding!).
	 *
	 * @param   string  $cipherText  The ciphertext to encrypt
	 * @param   string  $key         The raw binary key (will be zero-padded or chopped if its size is different than the block size)
	 *
	 * @return  string  The raw unencrypted binary string.
	 */
	public function decrypt($cipherText, $key)
	{
		$iv_size    = $this->getBlockSize();
		$key        = $this->resizeKey($key, $iv_size);
		$iv         = substr($cipherText, 0, $iv_size);
		$cipherText = substr($cipherText, $iv_size);
		$plainText  = openssl_decrypt($cipherText, $this->method, $key, $this->openSSLOptions, $iv);

		// Remove the zero padding
		return rtrim($plainText, "\0");
	}

	/**
	 * Is this adapter supported?
	 *
	 * @return  boolean
	 */
	public function isSupported()
	{
		if (!\function_exists('openssl_get_cipher_methods'))
		{
			return false;
		}

		if (!\function_exists('openssl_random_pseudo_bytes'))
		{
			return false;
		}

		if (!\function_exists('openssl_cipher_iv_length'))
		{
			return false;
		}

		if (!\function_exists('openssl_encrypt'))
		{
			return false;
		}

		if (!\function_exists('openssl_decrypt'))
		{
			return false;
		}

		if (!\function_exists('hash'))
		{
			return false;
		}

		if (!\function_exists('hash_algos'))
		{
			return false;
		}

		$algorithms = openssl_get_cipher_methods();

		if (!\in_array('aes-128-cbc', $algorithms))
		{
			return false;
		}

		$algorithms = hash_algos();

		if (!\in_array('sha256', $algorithms))
		{
			return false;
		}

		return true;
	}

	/**
	 * Returns the encryption block size in bytes
	 *
	 * @return  integer
	 */
	public function getBlockSize()
	{
		return openssl_cipher_iv_length($this->method);
	}
}
