GSoC 2017 – wlan slovenija – HMAC signing of Nodewatcher data and IPv6 support for Tunneldigger


I am a student at Faculty of Computer and Information Science in Ljubljana, Slovenia. Like (almost) every “computer enthusiast” I liked gaming and later found myself developing an OpenGL graphics engine. All engrossed in C++ and all sorts of algorithmic challenges I slowly came to realize that something is missing. Yes, my knowledge of anything network related. So, combining my two other interests, those being information security and inexplicable love of tunnels, I applied myself to Google Summer Of Code with the following ideas. As a participant in this year’s Google Summer of Code I will develop some new goodies for two projects of wlan slovenija open wireless network.

The first one is for the nodewatcher, which is an open source system for planning, deployment and monitoring of the wireless network. It is a centralized web interface which is also used for generating on OpenWrt based firmware images for specific nodes. After flashing the wireless router with the generated image, it just needs to be fed some electricity and it automatically connects into the network using VPN, or in case of an existing nearby node wirelessly. Nodwatcher then collects all the data about node’s performance by connecting to nodes to obtain data, or by nodes pushing their data to nodewatcher. This data is not sensitive, but we can still worry about it being manipulated or faked while in transit between the node and nodewatcher. The problem though is that all the monitoring reports are currently unsigned. This poses a security risk in the form of a spoofing attack, where anyone could falsify the messages sent to the nodewatcher. The solution is to assign a unique nodewatcher signing key to every node. The node will then sign the monitoring output using a hash function in HMAC (Hash-based message authentication code) mode. This means that a computed “signature” would be sent along with every message and nodewatcher can check whether the data was altered in any way. In the event of a signature verification failure a warning will be generated within the nodewatcher monitoring system. This is imporatant, because it assures the integrity of recieved data and inspires confidence in using it to plan deployment of new nodes in the future.

The second contribution will be to the Tunneldigger, which is a simple VPN tunneling solution based on L2TPv3 tunnels. It is used to connect nodes which do not have a wireless link between them in to a common network. Using existing network connectivity it creates L2TP tunnels between nodes. The current limitation is that tunnels can only be established over IPv4. This poses a problem because due to dramatic growth of the internet, the depletion of the pool of unallocated IPv4 addresses is anticipated for some time now. The solution is the use of its successor, IPv6. Since the tunnels are already capable of carrying IPv6 traffic, the capability of establishing them over IPv6 will be developed. The Tunneldigger will also support IPv4/IPv6 mixed environment where both server and client have some form of IPv6 connectivity. That way the Tunneldigger will finally be made future proof!

Reports about my work will be available on developers mailing list.

Yay for the free internet!

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