1. A method for identifying communication devices that serve as endpoints in the same communication session and for establishing correlations between the users of the communication devices, the method comprising: monitoring a plurality of traffic flows exchanged over a communication network; determining respective temporal traffic features for the monitored traffic flows; identifying communication devices that participate in a same communication session, by finding a match among respective temporal traffic features of the traffic flows exchanged by the communication devices; wherein determining the temporal traffic features comprises generating a respective compressed-form signature for each of the traffic flows, and wherein finding the match comprises comparing among signatures of at least some of the traffic flows exchanged by the communication devices; and wherein finding the match comprises matching the temporal traffic features between an inbound traffic flow of a first communication device and an outbound traffic flow of a second communication device.