Telex

From P2P Foundation
Jump to: navigation, search


= circumventing state-level Internet censorship


URL = https://telex.cc/


Description

By J. Alex Halderman:

"Telex, a new approach to circumventing state-level Internet censorship. Telex is markedly different from past anticensorship efforts, and we believe it has the potential to shift the balance of power in the censorship arms race.

What makes Telex different from previous approaches:

  • Telex operates in the network infrastructure — at any ISP between the censor's network and non-blocked portions of the Internet — rather than at network end points. This approach, which we call “end-to-middle” proxying, can make the system robust against countermeasures (such as blocking) by the censor.
  • Telex focuses on avoiding detection by the censor. That is, it allows a user to circumvent a censor without alerting the censor to the act of circumvention. It complements anonymizing services like Tor (which focus on hiding with whom the user is attempting to communicate instead of that that the user is attempting to have an anonymous conversation) rather than replacing them.
  • Telex employs a form of deep-packet inspection — a technology sometimes used to censor communication — and repurposes it to circumvent censorship.
  • Other systems require distributing secrets, such as encryption keys or IP addresses, to individual users. If the censor discovers these secrets, it can block the system. With Telex, there are no secrets that need to be communicated to users in advance, only the publicly available client software.
  • Telex can provide a state-level response to state-level censorship. We envision that friendly countries would create incentives for ISPs to deploy Telex."

(https://freedom-to-tinker.com/blog/jhalderm/anticensorship-internets-infrastructure)


Discussion

How Telex Works

Telex "create(s) what is essentially a proxy server without an IP address. In fact, users don't need to know any secrets to connect. The user installs a Telex client app (perhaps by downloading it from an intermittently available website or by making a copy from a friend). When the user wants to visit a blacklisted site, the client establishes an encrypted HTTPS connection to a non-blacklisted web server outside the censor’s network, which could be a normal site that the user regularly visits. Since the connection looks normal, the censor allows it, but this connection is only a decoy.

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.

As the connection travels over the Internet en route to the non-blacklisted site, it passes through routers at various ISPs in the core of the network. We envision that some of these ISPs would deploy equipment we call Telex stations. These devices hold a private key that lets them recognize tagged connections from Telex clients and decrypt these HTTPS connections. The stations then divert the connections to anti­censorship services, such as proxy servers or Tor entry points, which clients can use to access blocked sites. This creates an encrypted tunnel between the Telex user and Telex station at the ISP, redirecting connections to any site on the Internet.

Telex doesn't require active participation from the censored websites, or from the non-censored sites that serve as the apparent connection destinations. However, it does rely on ISPs to deploy Telex stations on network paths between the censor's network and many popular Internet destinations. Widespread ISP deployment might require incentives from governments." (https://freedom-to-tinker.com/blog/jhalderm/anticensorship-internets-infrastructure)