Using PGP in WordPress

wp-pgp-email.php

<?php
/**
 * Plugin Name: WP PGP Email
 * Version: 0.1
 * Description: Provides mechanism to encrypt outgoing email using PGP
 * Author: Tim Nash
 * Author URI: https://timnash.co.uk
 * Plugin URI: https://timnash.co.uk/wordpress-pgp-email
 *
 *
 * License: GPLv2 or later
 *
 *
 *	This program is free software; you can redistribute it and/or
 *	modify it under the terms of the GNU General Public License
 *	as published by the Free Software Foundation; either version 2
 *	of the License, or (at your option) any later version.
 *
 *	This program is distributed in the hope that it will be useful,
 *	but WITHOUT ANY WARRANTY; without even the implied warranty of
 *	MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *	GNU General Public License for more details.
 *
 *	You should have received a copy of the GNU General Public License
 *	along with this program; if not, write to the Free Software
 *	Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
 */

/**
 * Don't call this file directly.
 */
if ( ! class_exists( 'WP' ) ) {
	die();
}

class wpPGP{

	function __construct()
	{
		add_action('init', array($this, 'init'));
	}

	function init()
	{
		//Add email filter
		add_filter('wp_mail', array($this, 'filter_email'));

		//Add Form actions for user profile
		add_action('show_user_profile', array($this, 'add_profile_field'));
		add_action('edit_user_profile', array($this, 'add_profile_field'));
		add_action('personal_options_update', array($this, 'save_profile_field'));
		add_action('edit_user_profile_update', array($this, 'save_profile_field'));

	}

	//Get key for user or return false if no key is found
	static function get_key( $user_id = false )
	{
		if( !$user_id ) return null;

		return get_user_meta( $user_id, 'pgp_key', true );
	}

	//Set a key for a specific user, overriding any existing key.
	static function set_key( $user_id = false, $key = false )
	{
		if( !$user_id || !$key ) return null;
			//@todo validate key
		return update_user_meta( $user_id, 'pgp_key', $key);
	}

	//Remove key from database, if $match = true only remove if $key matches existing key otherwise error

	static function remove_key( $user_id = false, $key = false, $match = false )
	{
		if( !$user_id || !$key ) return null;
		$check_key = FALSE;
		if($match)
		{
			$check_key = $key;
		}

		return delete_user_meta( $user_id, 'pgp_key', $check_key );
	}

	//Encrypt contents using users key, if force is set to false and no key found return unencrypted content, if set to true return false.
	static function encrypt_contents( $user_id = false, $contents = false, $force = false )
	{
		if( !$user_id || !$contents ) return null;
		require_once 'libs/GPG.php';
		$gpg = new GPG();
		$key = self::get_key( $user_id );

		if(!$key){
			if($force)
			{
				return false;
			}
			else
			{
				return $contents;
			}
		}

		//we have a key and contents, let's encrypt it
		// create an instance of a GPG public key object based on ASCII key
		$pub_key = new GPG_Public_Key($key);

		// using the key, encrypt your plain text using the public key
		return $gpg->encrypt($pub_key,$contents);
		

	}

	static function validate_key_type( $key )
	{
		var_dump($key);

		require_once 'libs/GPG.php';
		$gpg = new GPG();
		$pub_key = new GPG_Public_Key($key);

		return $pub_key->GetKeyType();
	}

	//Filters WP_MAIL and encrypts content if being sent to a user with PGP key in the DB
	function filter_email( $args )
	{
		//Check if the email is being sent to a user
		$user = get_user_by( 'email', $args['to'] );
		if($user){
			if(self::get_key( $user->ID ))
			{
					if($args['message'])
					{
						$encrypted_contents = self::encrypt_contents( $user->ID, $args['message']);
						if($encrypted_contents) $args['message'] = $encrypted_contents;
					}
					//For people using the Mandril plugin
					elseif($args['html'])
					{
						$encrypted_contents = self::encrypt_contents( $user->ID, $args['html']);
						if($encrypted_contents) $args['html'] = $encrypted_contents;
					}

			}
		}
		return $args;
	}

	/*
	 *
	 * Admin Views
	 * These really should be in there own class but for this example we will leave them here
	 *
	 */

	function add_profile_field( $user )
	{
		
		$pgp_key = self::get_key( $user->ID);
		//Well this is unpleasant but very WordPressy
		?>
			<h3><?php _e('Email Encryption', 'wp-pgp-email'); ?></h3>
			<table class="form-table">
			<tbody>
				<tr>
					<th>
						<label for="pgp"><?php _e('Public PGP Key','wp-pgp-email'); ?></label>
					</th>
					<td>
					<textarea name="pgp" id="pgp" rows="5" cols="30"><?php if($pgp_key) echo $pgp_key; ?></textarea>
					<br>
					<?php if($pgp_key){ ?>
						<span class="description">KeyType: <?php echo self::validate_key_type($pgp_key); ?></span>
					<?php } ?>
					</td>
				</tr>
			</tbody>
			</table>
		<?php
	}

	function save_profile_field( $user_id )
	{
		if ( !current_user_can( 'edit_user', $user_id ) )
		return false;

		$key = $_POST['pgp'];

		return self::set_key( $user_id, $key );

	}
}

$wp_pgp_email = new wpPGP;

Required lib https://github.com/jasonhinkle/php-gpg

Hi,

Really useful code, thanks. However I've found a bug that stops it working. The incoming parameter to the encrypt_contents function is $contents plural. However the return on line 110 encrypts the variable $content (singular). This seems to result in a corrupt block that I can't decrypt.

Hope that saves someone else the head scratching I've just gone through!

Cheers,

--Toby

This is a great general pattern but is missing a few key pun intended) features and WordPress integrations. Have a look at the WP PGP Encrypted Emails plugin for a more complete solution to protect outgoing emails.

@meitar the mentioned plugin uses the same library, take a look at the code in the subversion repository.

Anyway, I highly recommend https://github.com/singpolyma/openpgp-php as there are many security related issues in php-gpg (ECB mode for example instead of CBC)

Thanks Daniel! As you probably know, WP PGP Encrypted Emails is now using the library you suggested. :)