Friday, February 24, 2006

Thunderbird as a deployment vehicle

One of the reasons for success of Skype is that they already had a deployment vehicle in the form of KaZaA file sharing network. I believe that for mass deployment of any P2P VoIP tool including open standard based P2P-SIP we need free software availability and a deployment vehicle.

Deployment vehicle is just a mechanism or tool that already exists and is widely used, e.g., tools for email, web, file sharing, or something more basic as Windows OS. For example, someone can add P2P-SIP support in popular email clients such as Microsoft Outlook Express or Mozilla Thunderbird. The latter is easier since it is open source.

Project description: the Thunderbird client can be extended to also serve as a (peer-to-peer) voice and IM client. IM buddies would appear in the Thunderbird address book, allowing to display buddies and their online status. IM transcripts might be saved and searched in the same way that messages are saved. This work can leverage a SIP project,, and might build on the Cockatoo project at

One issue is that not many people use Thunderbird compared to Microsoft product (although I believe that will change in future). Alternatively, a web interface similar to Gmail and google-talk can be provided that can be easily accessed from any web browser. The challenge is to use P2P instead of central web server.

Email based identity in P2P-SIP

Our p2p-sip architecture (see the previous 'external DHT' post) suggests using email address as user identity for SIP. In particular, our web CGI script (as a certifying authority, CA) generates the user certificate verifying that the user owns the identifier, say, and send this to the email address

This serves two purposes: (1) no login server: unlike Yahoo/MSN/Skype that need to connect to 'login server' on every login attempt, our p2p-sip uses the (central) CA only for first time use. The user certificate also gets stored in the P2P network, thus no need to connect to the 'login server' again. (2) any identity provider: unlike Yahoo/MSN/Skype/G-Talk that tie the identifier to a particular provider (i.e., for Yahoo users), we can allow any user identifier as long as the identifier belongs to him.

To avoid use of a single identity (service) provider, one option is to use user's email address as his SIP user id. Thus, identity verification just involves making sure that his user id is a valid email address that belongs to him, and that user has a certificate that proves this.

Our web CGI script generates user certificate, where the user public key and certificate request is supplied by the user (automatically by sipc, on first time use). But to make sure that the user id is his email address, the certificate is sent in the email. This prevents you from using user id "" because you can't get a certificate from our CA unless you own this email address. But if you have an email address say "" or "" you can use this as your SIP identifier in p2p-sip, thus not tied to a single provider.

Sending in email is just one of the ways. Alternatively, if a group of users already have user certificates from other trusted entity such as verisign, they don't need to do email based certificates. Another possibility for future work is to also allow 'tel:' identity if the user can call from that telephone number (with caller id) to our VoiceXML service script that verifies that the user owns this telephone number and issues a new certificate (by directly storing in the DHT). This way other friends who know his phone number instead of email address, can also reach him on p2p-sip. Making an outbound call to tel: (similar to sending outbound email) for identity verification is probably not a good idea, unless user somehow pays for the call.

Identity protection (no one else can steal your identity) and verification (others can verify that you own this identity) is just one part of the P2P-SIP security. And using an email-based identity moves the problem of identity issuance and protection from P2P-SIP to your email provider.

Wednesday, February 22, 2006

Using an external DHT as a SIP location service

In Dec last year, I added support for an external DHT in my SIPpeer application, i.e., the SIP-using-P2P model. A technical report describes the details. In particular I used OpenDHT and built signing and encryption on top of it to allow secure P2P SIP with identity protection. The advantage of using a managed external P2P network is that we can safely assume that OpenDHT nodes are trusted in the sense that they perform DHT routing correctly. Thus the security problem is partly solved, and the identity protection can be done by issuing a certificate to the user if he/she has an email address.

Then in Jan and Feb this year, I wrote a Tcl based SIPpeer connector for OpenDHT, and with the help of Xiaotao Wu, added it to our SIP user agent, sipc. We are trying to see if we can make it opensource or at least freely downloadable for non academic use also. But first I will need to fix some of the usability issues. I will keep the current status posted here on time to time.