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If by "other comments" you meant your own single comment which defended Signal's use of phone numbers by claiming "using phone numbers allows Signal to piggybac

If by "other comments" you meant your own single comment which defended Signal's use of phone numbers by claiming "using phone numbers allows Signal to piggyback on people's local contact databases instead of maintaining that directory serverside", that does not prevent Signal from keeping a database of contacts serverside. Further, they could have simply let users find and verify each other out-of-band, as PGP did with key distribution and fingerprint verification. There is absolutely no need for Signal to know my phone number, and it requiring one has been the main reason why I haven't used it.

tptacek 7y ago
Using phone numbers doesn't prevent Signal from storing a database of who's talking to who serverside. Not using phone numbers would require them to do so, and, as you can see from other secure messengers that made different tradeoffs (like Wire), that's exactly what ends up happening. It's pretty funny to try to use PGP as an example of a system that doesn't centralize and leak metadata.
- pmoriarty 7y ago
  How is PGP (now gpg) centralized? Out of band, I can exchange keys and verify fingerprints with whomever I want to communicate with, then send then a pgp/gpg encrypted email directly (or use some other means of sending the encrypted message). No centralization required. As for Signal, there's no requirement for them to keep any kind of directory, with or without phone numbers. Just let people discover each other in some way not under Signal's control. Whether other services have made the same mistake as Signal is irrelevant. It's still a mistake.
  - tptacek 7y ago
    This point is so straightforward that at some point your inability to acknowledge it will become willful. It is simple: People expect to find their acquaintances to talk to in a messaging application. Most messaging applications solve this problem by keeping a serverside contact database. You see the same thing with Signal's competitors. Signal refuses to keep that database, because it is practically as valuable to adversaries as message plaintext. So, instead of having users register handles and maintaining a database, Signal uses phone numbers --- like the most popular messaging applications, including WhatsApp, iMessage, and SMS --- so that it can take advantage of contact databases users have locally and not need to store a contact directory globally. "Just letting people discover each other some other way" doesn't work, and PGP is a good example of why: the "other way" PGP came up with is (wait for it) a global directory of key metadata. You are free to disagree with the tradeoff Signal made here. What you cannot reasonably do is suggest that there was no tradeoff, or that their use of phone numbers is somehow obviously flawed and privacy-hostile. It is, as I said, the opposite: phone numbers are an instance where Signal sacrificed uptake and UX in favor of privacy, because they do not care what random people on message boards have to say about their decisions as much as they care about the fact that they're the world's most important and effective secure messaging design.
    - pmoriarty 7y ago
      "People expect to find their acquaintances to talk to in a messaging application." That hasn't been the case in my use of Skype, for instance. I'm not sure if it's changed, but when I used it it had no real name requirement, and the people I communicated with over it had to tell me their Skype usenames out-of-band, like through email or by phone. There was no directory that would have been useful to us, as we didn't use our real names (or phone numbers). So your assertion that people on messaging applications expect to find their acquaintances (through it) is simply false in the case of Skype, which is one of the most popular messaging applications in existence. Discord is another extremely popular messaging application that didn't require me to give my name or phone number. "Signal refuses to keep that database, because it is practically as valuable to adversaries as message plaintext." And a database of phone numbers is not? "the "other way" PGP came up with is (wait for it) a global directory of key metadata." If you're talking about pgp/gpg keyservers, those aren't necessary for communication via pgp/gpg, as keys can be exchanged and verified by other means. Furthermore, the entities (plural) most people communicate through using pgp/gpg (ie. mail servers) don't control the keyservers, so they're not centralized like Signal is. This is a distributed system. "What you cannot reasonably do is suggest that there was no tradeoff, or that their use of phone numbers is somehow obviously flawed and privacy-hostile." I can't believe that you can't see that requiring people to hand over their phone numbers is a violation of privacy, or that it could in fact be objectionable to people who care about their privacy. It's even more mind boggling that you'd argue that handing over one's phone number offers more privacy than not doing so. This is akin to Facebook's real name policy, and arguably even worse, as so much tracking is tied to one's phone.
      - shawndrost 7y ago
        > That hasn't been the case in my use of Skype, for instance. You have misread his point. He's not saying that users expect to see their contacts on their "first load". He's saying they expect to see their contacts after adding them. Skype does fulfill that expectation, by keeping metadata about your contact list on their servers. Signal fulfills that expectation without keeping the metadata, by deferring to your phone's (local) contact system.

tptacek 7y ago

Using phone numbers doesn't prevent Signal from storing a database of who's talking to who serverside. Not using phone numbers would require them to do so, and, as you can see from other secure messengers that made different tradeoffs (like Wire), that's exactly what ends up happening. It's pretty funny to try to use PGP as an example of a system that doesn't centralize and leak metadata.

pmoriarty 7y ago
How is PGP (now gpg) centralized? Out of band, I can exchange keys and verify fingerprints with whomever I want to communicate with, then send then a pgp/gpg encrypted email directly (or use some other means of sending the encrypted message). No centralization required. As for Signal, there's no requirement for them to keep any kind of directory, with or without phone numbers. Just let people discover each other in some way not under Signal's control. Whether other services have made the same mistake as Signal is irrelevant. It's still a mistake.
- tptacek 7y ago
  This point is so straightforward that at some point your inability to acknowledge it will become willful. It is simple: People expect to find their acquaintances to talk to in a messaging application. Most messaging applications solve this problem by keeping a serverside contact database. You see the same thing with Signal's competitors. Signal refuses to keep that database, because it is practically as valuable to adversaries as message plaintext. So, instead of having users register handles and maintaining a database, Signal uses phone numbers --- like the most popular messaging applications, including WhatsApp, iMessage, and SMS --- so that it can take advantage of contact databases users have locally and not need to store a contact directory globally. "Just letting people discover each other some other way" doesn't work, and PGP is a good example of why: the "other way" PGP came up with is (wait for it) a global directory of key metadata. You are free to disagree with the tradeoff Signal made here. What you cannot reasonably do is suggest that there was no tradeoff, or that their use of phone numbers is somehow obviously flawed and privacy-hostile. It is, as I said, the opposite: phone numbers are an instance where Signal sacrificed uptake and UX in favor of privacy, because they do not care what random people on message boards have to say about their decisions as much as they care about the fact that they're the world's most important and effective secure messaging design.
  - pmoriarty 7y ago
    "People expect to find their acquaintances to talk to in a messaging application." That hasn't been the case in my use of Skype, for instance. I'm not sure if it's changed, but when I used it it had no real name requirement, and the people I communicated with over it had to tell me their Skype usenames out-of-band, like through email or by phone. There was no directory that would have been useful to us, as we didn't use our real names (or phone numbers). So your assertion that people on messaging applications expect to find their acquaintances (through it) is simply false in the case of Skype, which is one of the most popular messaging applications in existence. Discord is another extremely popular messaging application that didn't require me to give my name or phone number. "Signal refuses to keep that database, because it is practically as valuable to adversaries as message plaintext." And a database of phone numbers is not? "the "other way" PGP came up with is (wait for it) a global directory of key metadata." If you're talking about pgp/gpg keyservers, those aren't necessary for communication via pgp/gpg, as keys can be exchanged and verified by other means. Furthermore, the entities (plural) most people communicate through using pgp/gpg (ie. mail servers) don't control the keyservers, so they're not centralized like Signal is. This is a distributed system. "What you cannot reasonably do is suggest that there was no tradeoff, or that their use of phone numbers is somehow obviously flawed and privacy-hostile." I can't believe that you can't see that requiring people to hand over their phone numbers is a violation of privacy, or that it could in fact be objectionable to people who care about their privacy. It's even more mind boggling that you'd argue that handing over one's phone number offers more privacy than not doing so. This is akin to Facebook's real name policy, and arguably even worse, as so much tracking is tied to one's phone.
    - shawndrost 7y ago
      > That hasn't been the case in my use of Skype, for instance. You have misread his point. He's not saying that users expect to see their contacts on their "first load". He's saying they expect to see their contacts after adding them. Skype does fulfill that expectation, by keeping metadata about your contact list on their servers. Signal fulfills that expectation without keeping the metadata, by deferring to your phone's (local) contact system.