What advantage does Signal protocol have over basic public key encryption?

[Karl]

On 1/25/21, Punk-BatSoup-Stasi 2.0 <punks at tfwno.gf> wrote:
> On Mon, 25 Jan 2021 13:57:21 -0500
> Karl <gmkarl at gmail.com> wrote:
>
>
>> 4. perfect forward secrecy.  addresses the issue with pgp where future
>> advancements decrypt all your messages
>
> 	As far as I understand it, what signal and other systems do is generate
> 'ephemeral' keys (per session or even per message).
>
> 	Now, if all  traffic is recorded (which of course it is), and the key
> exchange broken thanks to say 'quantum computers', then the 'ephemeral' keys
> can be re-created. So as far as I can tell your claim is  wrong, and
> 'perfect forward secrecy' is a misleading marketing term.
>
> 	But I might have got it wrong myself...

Well, I'm too foggy nowadays to understand the protocol, but I read it long ago.

The term is mathematical rather than marketing.  Obviously if you
capture/recreate the private data when it is created you can decrypt
everything, because you then are one of the phones.

>> 5. metadata encryption.  pgp does not do this
>
>
> 	neither does signal. Or rather
>
> 	https://en.wikipedia.org/wiki/Signal_Protocol#Metadata
>
> 	"In October 2018, Signal Messenger announced that they had implemented a
> "sealed sender" feature into Signal, which reduces the amount of metadata
> that the Signal servers have access to by concealing the sender's
> identifier."
>
> 	Not sure what that actually means. Also
>
> 	"The Signal Protocol does not prevent a company from retaining information
> about when and with whom users communicate."
>
> 	Of course the protocol does not prevent the server from KNOWING who talks
> to whom...

What's important to understand here is that these developers are
cryptographers.  When they say "metadata that the signal servers have
access to" or "does not prevent a company from retaining information"
they are talking about much smaller bits of data than people usually
talk about.

Email server: "your metadata is encrypted and private because our
privacy policy says it is"
Cryptographer: "your encrypted message could be read because there is
a mathematical trail of the statistical distribution of keystrokes in
the public record of battery use, so don't trust this with something
important"

But yeah, never trust what someone says.  You have to look at the
specificaiton and the implementation to know what's really going on.
Signal said they do not prioritise nation-state anonymity back in the
day.  Back in that day, it was also reasonable to use a different
network than Signal's for communications.