What once was old

Ever heard of Telex?

I have. It’s old. Or was. Not anymore. Telex is the term being used to describe an experimental system for proxy-less access to the internet. It is based on that mouthful of a word, “public key steganography”.

I first saw the topic mentioned while reading an InfoSecIsland post earlier today. This is a comment from the University of Michigan researcher who developed Telex:

The main idea behind Telex is to place anti-censorship technology into the Internet’s core network infrastructure, through cooperation from large ISPs.

That quote, and the infographic below are from the Telex website. Actually, it is more of a flow chart, giving an overview of how Telex would work. Click on the image to view it full sized.
Telex overview

The researchers who thought of this approach are J. Alex Halderman at the University of Michigan, and Ian Goldberg of the University of Waterloo. An article in Threatpost, Researchers develop proxy less anonymity system differentiates Telex from alternatives:
[Telex] has a couple of fundamental differences from other anti-censorship or anonymity tools such as Tor or proxy networks… it uses “stations” installed at ISPs to recognize and reroute specially tagged requests from clients trying to reach censored sites.

Why aren’t those stations visible to censors?

Because the requests are part of an HTTPS connection to a site that the censor or government allows. Similar to Tor, each user would need a copy of the Telex client on his or her computer. The Telex client would generate the requests and insert the secret tags.

As for the secret tags and “public key steganography”, well, this is how Halderman explains it in his blog post Freedom to tinker: Anticensorship, Internets and Infrastructure:

The client secretly marks the connection as a Telex request by inserting a cryptographic tag into the headers. We construct this tag using a mechanism called public-key steganography. This means anyone can tag a connection using only publicly available information, but only the Telex service (using a private key) can recognize that a connection has been tagged.

Note that it is possible to implement Telex with, and ONLY with, the complicity of cooperative ISP’s. Nothing wrong with that, just wanted to mention it though. Halderman offers the following illustration of how Telex could function as a new approach to circumventing state-level Internet censorship:
halderman telex

The creators of Telex will be presenting their findings in a paper next month, August 2011, at a Usenix Symposium. The paper can be downloaded here.

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