Disguising Tor Traffic as Skype Video Calls-Bruce Schneie
April 23, 2012
Crypto-Gram: April 13, 2012
To prevent the Tor traffic from being recognized by anyone analyzing the network flow, SkypeMorph uses what’s known as traffic shaping to convert Tor packets into User Datagram Protocol packets, as used by Skype. The traffic shaping also mimics the sizes and timings of packets produced by normal Skype video conversations. As a result, outsiders observing the traffic between the end user and the bridge see data that looks identical to a Skype video conversation.
The SkypeMorph developers chose Skype because the software is widely used throughout the world, making it hard for governments to block it without arousing widespread criticism. The developers picked the VoIP client’s video functions because its flow of packets more closely resembles Tor traffic. Voice communications, by contrast, show long pauses in transmissions, as one party speaks and the other listens.