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I was expecting to hear about someone who got a new phone, set up Signal using the phone number, and then communicated with contacts without any more authentica

I was expecting to hear about someone who got a new phone, set up Signal using the phone number, and then communicated with contacts without any more authentication. This doesn't appear to be anything of the kind. Signal has implemented a migration system so that people can move to a new phone without changing the safety number. Then a bunch of references to the promises Signal makes about re-verifying if the safety number changes. Since the safety number doesn't change, none of those actually apply.

dv_dt 5y ago
I imagine there is a human factors tradeoff here. If signal notified on each migration, users with even medium sized contact lists would likely be getting constant notifications - making the alert useless. See medical device or aviaton alerts experiences.
- TheAceOfHearts 5y ago
  The problem is that there's no one size fits all solution. Security is all about making tradeoffs based on your threat models. I think this is probably a sensible default for many people engaging in casual conversations. However, this notification should probably be configurable. That way you can be notified when communicating with high risk individuals.
  - geofft 5y ago
    What threat model would it protect against? The thing this proposed change would protect against is, if an attacker gets access to a participant's unlocked phone, and then transfers their Signal account, it will notify the other participants. But an attacker can just as easily retain access to the original phone and send and receive messages with it - either physically, or by installing malware (a RAT or something) and remotely accessing the phone. And when you move devices, because of the way the Signal ratchet works (I think), the original device doesn't get access to send or receive messages. So a device move is detectable if the original phone is returned.
- whoknowswhat11 5y ago
  You basically lose trust after 2 false alerts. Third false alarm in college - no one left dorm. Third false alarm working overseas (required we wake up etc) everyone turned off buzzers.
- katbyte 5y ago
  What’s up always notified you inline in chats and it worked out just fine even for larger group chats
- upofadown 5y ago
  Not in this case. If the long term identity is transferred from device to device there is no extra risk to trade off. It is like copying your PGP private keys from one device to another. The associated public keys are still in your correspondents key stores, certified or not. Nothing changes for them and there is no reason for them to know what you have done. There is nothing here for Signal to do. Their issue is is the one that everyone who creates an encrypted E2EE messenger faces. There is no good analogy for cryptographic identities. So it is hard to produce a good conceptual model that the user can use to understand what they should expect and how they should react.

dv_dt 5y ago

I imagine there is a human factors tradeoff here. If signal notified on each migration, users with even medium sized contact lists would likely be getting constant notifications - making the alert useless. See medical device or aviaton alerts experiences.

TheAceOfHearts 5y ago
The problem is that there's no one size fits all solution. Security is all about making tradeoffs based on your threat models. I think this is probably a sensible default for many people engaging in casual conversations. However, this notification should probably be configurable. That way you can be notified when communicating with high risk individuals.
- geofft 5y ago
  What threat model would it protect against? The thing this proposed change would protect against is, if an attacker gets access to a participant's unlocked phone, and then transfers their Signal account, it will notify the other participants. But an attacker can just as easily retain access to the original phone and send and receive messages with it - either physically, or by installing malware (a RAT or something) and remotely accessing the phone. And when you move devices, because of the way the Signal ratchet works (I think), the original device doesn't get access to send or receive messages. So a device move is detectable if the original phone is returned.
whoknowswhat11 5y ago
You basically lose trust after 2 false alerts. Third false alarm in college - no one left dorm. Third false alarm working overseas (required we wake up etc) everyone turned off buzzers.
katbyte 5y ago
What’s up always notified you inline in chats and it worked out just fine even for larger group chats
upofadown 5y ago
Not in this case. If the long term identity is transferred from device to device there is no extra risk to trade off. It is like copying your PGP private keys from one device to another. The associated public keys are still in your correspondents key stores, certified or not. Nothing changes for them and there is no reason for them to know what you have done. There is nothing here for Signal to do. Their issue is is the one that everyone who creates an encrypted E2EE messenger faces. There is no good analogy for cryptographic identities. So it is hard to produce a good conceptual model that the user can use to understand what they should expect and how they should react.