Add option to lock the application

[shaaati]

While the phone app allows to lock the application with a passcode this is currently not possible on the desktop.
From time to time, I give friends the permission to use my PC, e.g., for managing a music playlist or for quickly looking up something on the internet.
Right now, everyone with access to my computer can open Chrome and look at all my synchronised conversations in Signal. I would feel more comfortable if I could, just as on the phone, set a passcode to unlock Signal on the desktop.

(I don't know anything about how Chrome apps store data but maybe this could as well be used to encrypt the database itself.)

[2-4601]

I believe you can do this with Chromium/Chrome profiles.

[Natanji]

As far as I know, even using Chrome profiles doesn't encrypt all the data. Note that for full security, Signal on Android/iOS never writes unenecrypted data to the device; but right now, as a user, I have no idea if this is also true for Signal Desktop.

Can we get a full list of locations where Signal Desktop stores data, to check if it's properly encrypted there (or to make sure ourselves via solutions like encfs)? @moxie0, I bet you know more about this.

And in any case, any encryption right now is simply foiled by the fact that we cannot enter a user-defined password yet...

[2-4601]

OP wanted to prevent friends from accidentally seeing Signal messages while still using the same computer. You can achieve this with profiles.

Data is stored in the profile directories https://www.chromium.org/user-experience/user-data-directory

Signal iOS does not have a password. That's leveraged to the OS. Android client has that feature. I guess mainly because TextSecure is so old (and older Android OS versions have lacked in that respect).
liliakai probably knows this app best, not moxie. In any case I think it's preferred here that this kind of discussion should go to the mailing list https://lists.riseup.net/www/info/whispersystems

[moxie0]

We're not going to be adding any local access control or protection. You can use Chrome profiles, full disk encryption, and a screenlock.