strongSwan

h1. An XML based management protocol for strongSwan (SMP)



We are developing a flexible XML-based configuration interface. It uses the *SMP* protocol developed by Andreas Eigenmann and Joël Stillhart as part of their diploma thesis.



h2. Overview



The currently implemented communication interface to [[charon]] is called stroke. It's a simple protocol with it's own binary format. Only the input format is specified, output is redirected to the console.

While this protocol is usable for console applications (ipsec/starter), we need a better protocol to get feedback for an operation, query the status of the daemon, ...



h2. Requirements

*

** Querying
** **** IKE_SA list
** **** Daemon status
** **** ...
* ** Control
** **** initiate connection
** **** terminate connection
** **** ...
* ** Get notifications
** **** client connected
** **** client connect attempt failed
** **** ...



h2. Protocol



To get an universal usable and easy to implement protocol, SMP is based on a XML. We use "Relax-NG":http://www.relaxng.org schemas for validation, as they are more powerful than DTD, but simpler than XML schema.



h3. Connectivity



SMP uses a reliable protocol. We implement the protocol over a Unix socket for the first try, TCP connections are targeted for a later release (see security).



h3. Security



We do not implement any security (encryption/authentication) in the first iteration. We will operate on a Unix socket, we enforce security with file permissions. Further development iterations will support for remote administration (over TCP), and then we need authentication, encryption and integrity checks.

The proposed XML-Security like approach proposed in the diploma thesis suffers from replay attack detection. Futher, using the asymmetric approach for each message may be to expensive.

If we implement a more complex notification mechanism, we need to register anyway at connection setup. We could agree on encryption and compression algorithm and exchange a key in this registration process.



h3. Message format



The root element of an exchanged element is the _<message>_ element. A message has a _type_ attribute of either _request_, _response_ or _notification_. To protect messages against replay attacks, each message as an _id_ attribute, which in unique and incremental for each request/response pair. Notifications use their own counter for for message ids, as they appear asynchronously.

Messages of _type_ _request_ and _response_ contain one or more of the elements _query_ and _control_.



h3. Schema



The complete schema is available at source:src/charon/plugins/smp/schema.xml [source:trunk/src/charon/plugins/smp/schema.xml] (draft).



h3. Query Operations



** [[SMPQueryIKESA|Query a list of IKE_SAs]]
** ...
The status of all IKE_SAs can be queried by sending a message of type _request_ including a query