[whispersystems] Signal and Metadata

Ira Bailey

2016-01-14 08:37:59 UTC

Great summary Finn, thanks for the clear write-up.

Ira.

"The server does not keep logs" is one of those claims that is, obviously,
impossible to verify, as you do not have access to the server. The Signal
app identifies itself to the server and tells it who it wants to connect
with, and the server contacts the other party's Signal app and connects the
two. Both ends encrypt the contents of the call, but the server can see who
called who, at what time and how long it lasted (assuming the encrypted
voice data goes through the server, which I'm pretty sure it does), as all
of this information is needed for it to create and maintain the connection.
So I would say that Signal does leave metadata and the Wikipedia article is
wrong. The operators of the server (Open Whisper Systems) promise not to
store any of this information (according to your quote from wikipedia, I
haven't seen that promise but I also haven't really gone looking). As far
as I'm aware, there is nothing preventing a government agency from
requiring them to silently start logging this data eg. with an NSL, nor
preventing Amazon, who the server(s) appear to be hosted with, from logging
this data, as they ultimately control the physical server. Also anyone who
compromises the credentials that OWS or Amazon use to manage the server(s)
would be able to start logging metadata. While a lot of this is somewhat
unlikely, unverifiable statements like "we don't keep logs" have become a
selling point for other purportedly pro-privacy companies, usually trying
to sell you something. In particular, providers of VPN services. This has
lead to a number of people touting these claims as though they were somehow
verifiable, which lead to others pointing out that they are not. Most of
these service providers have very little to base their reputation on, so
trusting their claims is difficult. the Open Whisper Systems developers
have a history of giving a shit about this sort of thing, and have actually
worked to reduce the amount they can log (by encrypting everything but the
metadata), making their claims of no logging somewhat more reputable.
This is my understanding of things, I may have gotten several/all parts
wrong.
Finn Herzfeld
After reading the wiki for Signal, I was under the impression that Signal
"Signal does not leave metadata about who called who and when because the
servers do not keep call logs." -
https://en.wikipedia.org/wiki/Signal_%28software%29#Servers
However, I'm repeatedly seeing posts on Hacker News, Reddit, and other
sites claiming that Signal does leave a metadata trail. Is this true? Would
someone please the implications of metadata with Signal? Is it similar to
Tor Browser, where the WIFI provider, governments, phone carrier, etc. can
only see that I'm accessing Tor Browser and not my browsing history?
Likewise with Signal, they can only see that I'm accessing Signal and not
that I'm contacting a specific person? Or, can they see more than that?