Giusto per segnalare l’esistenza di questo progetto, anche se non ho ancora avuto modo di provarlo e testarlo.

TorChat è una chat msn-like basata su TOR, che garantisce la cifratura (il traffico tor viaggia cifrato end-to-end) e l’autenticazione della conversazione,  oltre che l’anonimato della propra posizione.

TorChat is a peer to peer instant messenger with a completely decentralized design, built on top of Tor’s location hidden services, giving you extremely strong anonymity while being very easy to use without the need to install or configure anything.

TorChat just runs from an USB drive on any Windows PC. (It can run on Linux and Mac too, in fact it was developed on Linux with cross platform usability in mind from the very first moment on, but the installation on other platforms than Windows is a bit more complicated at the moment)

Riporto qualche stralcio dal sito ufficiale del progetto:

Encryption

All TorChat traffic is encrypted end-to-end.

There are some misunderstandings floating around regarding Tor and encryption. Whenever I mention Tor and encryption in the same sentence the immediate reflex response of many people is: “But Tor provides no encryption!” This statement is true for most applications but not for all. The most commonly known usage of Tor is to use it as an anonymizer for traffic between the anonymous user and a publicly available service in the Internet and while the traffic will travel encrypted through the Tor network it MUST at some point leave the Tor network and enter the unencrypted internet to reach its final destination. This is the origin of the above mentioned “Tor provides no encryption” and it is undoubtedly true for this most widely known and practiced application of Tor and users should understand it.

However, there exists another and less commonly known mode of operation in which two Tor clients can initiate a fully encrypted peer-to-peer connection between each other that will not leave the Tor network at any point! This is what TorChat is using. Both clients build a normal 3 node circuit from each end to some random tor node in the middle to “meet” there and connect their circuits with each other. Upon connection another layer of encryption is established reaching through from one client to the other, building one uninterrupted encrypted tunnel through all 6 nodes between the two end points. This means all TorChat traffic is end2end encrypted. There are no exit nodes involved in this mode, at no point other than your and your buddies own computer will the traffic ever leave the Tor network.

This less known Tor mode is called Tor hidden services, you can read more about it on the above link. It effectively allows true hidden peer-to-peer networks, there are just not many softwares that make any use of its peer-to-peer capability, most use it more in a traditional client-server manner, TorChat is one of the few (and at the moment I don’t know of any other).

Authentication

TorChat buddies authenticate themselves by proving that they are reachable though their .onion address.

The Tor hidden service protocol by itself has no built-in authentication mechanism for incoming connections but it can guarantee that when you initiate an outgoing connection to a given .onion address you can never end up at the wrong counterpart, the one who answers the connection is the one who is in possession of the private key belonging to this address (the private_key file in the hidden_service folder).

Therefore TorChat will not trust any incoming connection and instead immediately try to open an outgoing connection to call back any incoming buddy on the address he pretends to be. A random cookie will then be sent out by both clients on their (trusted) outgoing connection that must be correctly answered on the incoming connection. Only after the answer is found to be correct the incoming connection can be trusted, the status of the buddy will be displayed as on-line and incoming messages from this buddy will be accepted.

It is essential that you don’t lose the private_key file belonging to your ID because the one who finds it will be able to pretend to be you. Using a tool like TrueCrypt is a good idea when you intend to use TorChat on a portable USB drive as these devices can easily be lost or stolen.