[Cryptography] Signal planning to support for plaintext SMS

[Ralf Senderek]

On Sun, 30 Oct 2022, John Denker wrote:

> Crypto exists at the intersection of ethereal mathematics and
> down-to-earth engineering. Today we are discussing human-factors
> engineering.

Sure!

>  [...]                                         They need to
> start looking at it from the user's point of view, not from
> the app's point of view.

Of course!

> When there are two apps, if I want to find a message, I have
> to look in two places. Half the time this doubles the workload.
> This is a step backwards in terms of usability.

> By the same token, if I want to send a message, I have to
> choose which app to use. If I choose the SMS app, I will
> send an insecure message, even when it would have been
> possible to send a secure message. So this is backwards in
> terms of security as well as usability.

I think this assessment isn't plausible, because using two different
apps would certainly also split the set of users anyone communicates
with into people like Alice, who uses the new Signal and blokes
like Bob who never intends to send and receive a secure message.
So you'd know where to look when you search for a person's
message. And if you don't find Alice in the insecure app this is
a good reminder not to send her insecure messages as she don't 
want that to happen. I don't see why this would be a step
backwards in terms of security.

> There is a well-known discipline for analyzing decisions. It
> requires considering all the plausible possibilities and
> weighing the costs and benefits of each. For example, if the
> perceived problem is unwittingly sending an insecure message,

it is!

> there are about ten ways of addressing that. None of them are
> perfect, but some are better than others.
>   -- My guess is that a separate app is closer to the bottom
>    than the top of the list

That's where we disagree. IMHO if an app makes it almost impossible
to send an insecure message I regard that as a positive feature
from the point of security. That better security may (not must)
come at some cost of comfort is a well-known fact.

> By way of analogy: Suppose firefox and chrome required users
> to obtain separate browsers, from different suppliers, with
> different UIs, to distinguish HTTP from HTTPS sites. Are you
> telling me that security "demands" this?

A much better analogy would be the assumption, that chrome would never
use HTTP (and always HTTPS) and firefox would always use HTTP
and never HTTPS. Then you'd clearly know which one to use for 
online banking.

     --ralf