One possible solution is to only be able to contact someone if you have received an invitation code from them out of band. E.g. "scan this QR code to add me on signal". Such an invitation code should default to single-use but users should be allowed to generate standing invitations so that businesses and the like can print and post one in their store or whatever. Start getting spam from one of your standing invitations? Just revoke it and make a new one. Presumably the Signal folks can come up with more alternative solutions than the half baked one I came up with after thinking about it for a minute, they're clever cookies.
Welcome back to “key signing parties”. PGP never got enough adoption. At least Signal is simple enough that the (ahem) leaders of the US can (mostly) manage to use it.
Unfortunately, in an end to end encrypted messaging system, an identity is denoted by some sort of long number. That is an inescapable fact. Trusting a third party to correctly map, say, a phone number to a cryptographic identity number eventually results in the sort of attacks we have been seeing with phone oriented encrypted messengers recently like WhatsApp and Signal. The PGP people were doing the right thing when they were doing education in the form of key signing parties. That is something the user needs to know.
Anonymous messengers have no real choice and have to use some sort of number for identity. See Briar, Session or Tox for examples.
> attacks we have been seeing with phone oriented encrypted messengers recently like WhatsApp and Signal
Could you give an example of an actual attack of this kind on Signal? The 'Signalgate' event was someone mistakenly inviting the wrong person to a chat.
Allegedly, Signalgate was caused by Apple helpfully mapping the wrong number to a name. Then Signal mapped that number to the wrong cryptographic identity.
> Allegedly, Signalgate was caused by Apple helpfully mapping the wrong number to a name.
In what system is Apple mapping numbers to names? The address book is maintained by users. An AppleID? How could that happen? And it would seem to result in many errors before the Signal error.
I thought it was simply caused by someone adding the wrong person to the chat?
> The Intercept
Per that article, the cause is unknown. The speculated cause in the article is that The Intercept somehow lost control of the user id, and Signal recycles user ids. That seems like a bad practice generally and with this predictable consequence, and especially bad for an application people trust with security.
> Twilio
This was Twilio employees caught by a phishing attack. I wonder what more secure, and affordable, options Signal has. Operate their own SMS infrastructure - would that be more secure that Twilio's? Use something besides SMS - would on-boarding become too hard? Stop using phone numbers - they need some spammer and bot filter, so what replaces it?
> Russian State-Backed Hackers
A phishing attack on Signal users, using a QR or link to make the attacker a linked device. That setup seems risky for non-technical users; I wonder how Signal could better secure it.
That and other attacks are described here. The other attacks all require compromising the device on which Signal is installed:
Leaders of the US use an Israeli backdoored version of Signal (TM-Signal) TeleMessage by Smarsh was used by DOD, CPB, and others for records retention reasons... also hacked to smithereens.
People seem to get on with Discord invite links just fine. You don't have to do the "confirm that all these emoji are the same on both your devices" dance to stop spam.
> People seem to get on with Discord invite links just fine.
Discord is used by a narrow group of technically literate people. Signal is for everyone. Your grandparents probably don't use Discord, but if they can text then they can use Signal.
Imagine setting up a chat for an organization you're working with - will you be willing to process 20 out-of-band QR codes? 50?
On a smaller scale, it's clear that Signal believes a functioning address book is necessary for end user adoption. For example, by default Signal notifies you of people in your phone contacts who are on or who later join Signal.
> Presumably the Signal folks can come up with more alternative solutions
I have yet to see a solution better than the one they chose, for their requirements. Notice that there are none in this discussion.
