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> AFAIK, it prompts at first, maybe a few times, but then stops. It's been re-prompting me for years. If there's a time it stops, I haven't found it. > I am n

by gojomo 5y ago

> AFAIK, it prompts at first, maybe a few times, but then stops. It's been re-prompting me for years. If there's a time it stops, I haven't found it. > I am not sure how Signal backups work or that user contacts, encrypted, are backed up to the SGX enclave. Where does it say that? You're talking about backups. I'm talking about contact-discovery, wherein the client regularly sends (hashed versions of) all the phone numbers from your contacts (if you've shared them with the app) to Signal's servers, to let you (& them!) know you're both on Signal. How else would you think the notification you get when someone in your contact list joins Signal is generated? Signal's claim that these oft-repeated intersection operations leave no permanent records on their servers seemed (last I looked deeply) based on the SGX attestation: that your list is encrypted such that only the trusted code will process it. If Signal, or hackers, or Intel Corp, or the "Intel Community" can compromise SGX's guarantees, they can decrypt & log the full set of phone numbers uploaded. So again, it reduces to how much you trust Intel™ SGX®. (Also note that even if you do trust SGX, someone you've never met can, by having your phone number in their contacts, receive a notification when you join Signal. And separately from any SGX-mediated threats, a persistent attacker with privileged views of your devices' network traffic – such as via an ISP or mobile carrier – can get, via the volume & timing of traffic to and from Signal's servers, a pretty good idea of who you're talking to.)

wolverine876 5y ago
Could you provide documentation of that version of how Signal operates? You can see the links from Signal and Matthew Green that I supplied. > I'm talking about contact-discovery, wherein the client regularly sends (hashed versions of) all the phone numbers from your contacts (if you've shared them with the app) to Signal's servers If they are hashed, why do you need to trust anyone?
- gojomo 5y ago
  You can read Marlinspike's 2017 description of an approach they were then rolling out – & AFAIK still use – at: https://signal.org/blog/private-contact-discovery/ https://signal.org/blog/private-contact-discovery/ Note it relies on SGX for privacy. (Anything they did earlier may have involved even more trust of Signal Inc's servers.) Hashes across the (tiny!) space of all phone numbers are easy to reverse via brute-force. But also, again: how do you think Signal is able to notify you when any phone number in your contacts – even if you're not in theirs! – first joins Signal?
  - wolverine876 5y ago
    Thank you for the link! That helps a lot.

by gojomo 5y ago

wolverine876 5y ago

Could you provide documentation of that version of how Signal operates? You can see the links from Signal and Matthew Green that I supplied. > I'm talking about contact-discovery, wherein the client regularly sends (hashed versions of) all the phone numbers from your contacts (if you've shared them with the app) to Signal's servers If they are hashed, why do you need to trust anyone?

gojomo 5y ago
You can read Marlinspike's 2017 description of an approach they were then rolling out – & AFAIK still use – at: https://signal.org/blog/private-contact-discovery/ https://signal.org/blog/private-contact-discovery/ Note it relies on SGX for privacy. (Anything they did earlier may have involved even more trust of Signal Inc's servers.) Hashes across the (tiny!) space of all phone numbers are easy to reverse via brute-force. But also, again: how do you think Signal is able to notify you when any phone number in your contacts – even if you're not in theirs! – first joins Signal?
- wolverine876 5y ago
  Thank you for the link! That helps a lot.