Security experts counter that such arguments ignore the fact that even end-to-end encrypted technology leaves a trail of metadata behind that can be used to parse who is talking to whom, when and where. “Encryption is really good at making it difficult to hide the content of communications, but not good at hiding the presence of communications,” said Matt Blaze, a computer security expert at the University of Pennsylvania.

Source: Encrypted Messaging Apps Face New Scrutiny Over Possible Role in Paris Attacks