PortKnock

-- Overview --
This application is a simple port knocker for the iPhone, generally useful only to network administrators. You *must* have a port knock daemon running on your server for this application to be useful.
Features in this version of Port Knock:
- Password Protection
- Knock Validation
- Import/Export Hosts
- Auto App Launcher(+)
- Knock Progress Screen
- Shows your External IP Address
- Arbitrary number of ports per host
- An unlimited number of host definitions
- TCP/UDP configuration per port
- Selectively sending knocks through WiFi or Carrier/3G networks
- Configurable interpacket delay
- Has no advertising
-- Use Cases --
This app is ideal if you're on a WiFi network but don't have a port knocker on the available computers. If you're sitting behind a NAT, the iPhone/iPod Touch will have the same IP as any of the other computers on your network.
This is also great to use with TouchTerm or any other ssh or telnet software for the iPhone.Just give it the hostname and a list of ports, and whether you want it to send TCP or UDP packets.
-- Brief Description of Port Knocking for the Layman --
Port Knocking is a technique to secure services behind a firewall until a specific knock sequence is given. This is not to be confused with port scanning (a network management tool for discovering open services on a system).
Imagine you left your kids at home alone. You don't want them to open the door for strangers. And when a stranger comes knocking, you don't even want them to come to the door, because you don't want them to know your kids are there. But, when you or other family members come, you might want them to open the door for you. So you teach them to listen for a certain rattat-tat-tat or special knock that only you and your family know.
This is the same concept you can apply to your servers. If you run a knock daemon on your server, this app then lets you send the special knock to it.
A more technical description of port knocking can be found on Wikipedia:
http://en.wikipedia.org/wiki/Port_knocking

-- Additional Info --
If you're in need of a knock server, I personally use Judd Vinet's knock daemon for linux. It's quite easy to use: http://www.zeroflux.org/projects/knock
You can find of information and a nice list of other knock clients and servers over at
http://www.portknocking.org/
-- Notes --
+ There are some restrictions regarding the Auto App Launcher. For SSH, you can only create temporary connections. For Mail, you will always be shown a new compose mail window first. Unfortunately, this is due to the way App integration works on iOS. There's not much I can do to address these issues at this time.

-- Support --
For better support, please send bug reports and feature requests to [email protected], rather than simply posting it in a review.
You can find more info on using PortKnock at the main website:
http://www.sungheroes.com/products/portknock-iphone/
-- History --
2022-02-28 PortKnock 4.18 released. LaunchApp automatically works again. Fixed some import bugs.
2018-01-xx PortKnock 4.12 supports IPv6
2017-09-xx PortKnock 4.0 released for iOS 10.3
2013-02-15 PortKnock 3.2 should work again on iOS5
2011-Jul-10 PortKnock 3.0.833 released. Added password protection, knock validation, import/export hosts, auto app launcher, and knock progress screen.
2010-Dec-14 PortKnock 2.02 released. Added a 'copy hosts' feature. Host/Port reordering should now work correctly. Entry fields should now work properly on iOS 4.2.1.
2010-Sep-25 PortKnock 2.01 is now available in the app store. iPhone 4's should no longer have an issue. If you are experiencing problems, please email me.
2010-Sep-09 The iPhone4 issue should be resolved. A bug fix release has been submitted. Thank you all for your patience!