Last year, I outlined the specific requirements that an app needs to have in order for me to consider it a Signal competitor.

Afterwards, I had several people ask me what I think of a Signal fork called Session. My answer then is the same thing I’ll say today:

Don’t use Session.

The main reason I said to avoid Session, all those months ago, was simply due to their decision to remove forward secrecy (which is an important security property of cryptographic protocols they inherited for free when they forked libsignal).

Lack of forward secrecy puts you in the scope of Key Compromise Impersonation (KCI) attacks, which serious end-to-end encryption apps should prevent if they want to sit at the adults table. This is why I don’t recommend Tox.

And that observation alone should have been enough for anyone to run, screaming, in the other direction from Session. After all, removing important security properties from a cryptographic security protocol is exactly the sort of thing a malicious government would do (especially if the cover story for such a change involves the introduction of swarms and “onion routing”–which computer criminals might think sounds attractive due to their familiarity with the Tor network).

Unfortunately, some people love to dig their heels in about messaging apps. So let’s take a closer look at Session.