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I believe they have covered this question many times before, but I don’t see an answer on signal’s website. From memory, it had to do with not wanting to own th

I believe they have covered this question many times before, but I don’t see an answer on signal’s website. From memory, it had to do with not wanting to own the user’s contact list. Using a phone number allowed them to rely on a contact list on the users phone, which is not tied to the signal account. There was more nuance than that though.

charcircuit 4y ago
Why not just store a contact list of usernames on the phone though?
- dcow 4y ago
  What would this list contain? You don't have a signal username. If you did you'd have to claim it somehow (degenerates to email or phone verification). It's not that simple. Using phone numbers allows signal to plug into the existing state of the world and leverage it to upgrade the security of messaging for everyone who uses it. The one compromise is that it treats phone number as a short identifier (importantly, not cryptographic, it uses real crypto for that). If you don't use phone numbers, your product would look more like Keybase. You have to somehow facilitate key exchange between people in a way that's actually usable. Otherwise all your security benefits go out the window because nobody uses your product. Signal understands this nuance perfectly which is why they're a successful product.
- k1t 4y ago
  If I don't use Signal, then I'm not going to keep a list of my friends' Signal usernames on my phone. If I subsequently sign-up for Signal, then I have no way to discover which of them use Signal - short of contacting them via some other method and asking for their Signal username, if any. By making the Signal username the same as the user's phone number, I actually DO have a list of Signal 'usernames' on my phone already. As soon as I sign-up, I can send my list of friends' phone numbers to Signal and they can tell me which of those people have Signal accounts.
autoexec 4y ago
> it had to do with not wanting to own the user’s contact list. Using a phone number allowed them to rely on a contact list on the users phone, which is not tied to the signal account. That doesn't make any sense. Signal did the total opposite. It started keeping sensitive user data in the cloud including your name, your photo, your phone number, and a list of your contacts. It stores that data on their servers permanently.
- _6hmp 4y ago
  I don't think this is true, do you have a source? They store registered users phone numbers and allow discovery by making a request with a hashed version of the phone numbers on your contact list. They add an extra layer to allow attestation of the software doing this using Intel's secure enclave. They give many examples of responding to warrants with only whether the number has been registered and the timestamp of registration, which they explain is the only information they hold. Private Contact Discovery: https://signal.org/blog/private-contact-discovery/ https://signal.org/blog/private-contact-discovery/
  - autoexec 4y ago
    Your 2017 blog post is outdated. See: https://community.signalusers.org/t/can-signal-please-update-its-privacy-policy/15323 https://community.signalusers.org/t/can-signal-please-update... and https://community.signalusers.org/t/dont-want-pin-dont-want-anything-stored-in-cloud/14057/27 https://community.signalusers.org/t/dont-want-pin-dont-want-... See here for a discussion on how Intel's 'secure' enclave won't save you: https://community.signalusers.org/t/proper-secure-value-security-pins-are-too-easy-to-brute-force-sgx-is-not-reliable-enough/15096 https://community.signalusers.org/t/proper-secure-value-secu...
    - dcow 4y ago
      There's a horrible conflation of concepts here. A pretty big one. When people talk about cloud services, they generally mean part of an application that runs on the cloud that participates as a trusted actor in the application's trust model. What people in the linked thread are realizing is that "signal has a server" and they are confused because they thought signal didn't have a server, or something. So, what's important about Signals servers is that, outside of initial key exchange which is verified by two parties out of band, they are not a trusted entity, ever. When you send a message it goes through signals servers. When you sync your profile picture with other devices, same thing. The data transits signals servers. This is made possible because of cryptography. By encrypting the data in a way that is indecipherable by 3rd parties (Signal's servers included) your data is isomorphic to random noise. So, the only thing Signal needs to do is route the random noise to the right place. If it doesn't do that, it's a denial of service and about the only attack you're vulnerable to if you use Signal. Otherwise, the receiver gets the exact random noise that you sent, but only they can make sense of it because of the miracle of cryptography. If you're really doing to throw a fit because Signal syncs a profile picture between your devices using the same level of crypto as is used for messaging then you're honestly crazy. No. Signal did not "not have a cloud" and now they "have a cloud". Not by any reasonable interpretation of the events.

charcircuit 4y ago

Why not just store a contact list of usernames on the phone though?

dcow 4y ago
What would this list contain? You don't have a signal username. If you did you'd have to claim it somehow (degenerates to email or phone verification). It's not that simple. Using phone numbers allows signal to plug into the existing state of the world and leverage it to upgrade the security of messaging for everyone who uses it. The one compromise is that it treats phone number as a short identifier (importantly, not cryptographic, it uses real crypto for that). If you don't use phone numbers, your product would look more like Keybase. You have to somehow facilitate key exchange between people in a way that's actually usable. Otherwise all your security benefits go out the window because nobody uses your product. Signal understands this nuance perfectly which is why they're a successful product.
k1t 4y ago
If I don't use Signal, then I'm not going to keep a list of my friends' Signal usernames on my phone. If I subsequently sign-up for Signal, then I have no way to discover which of them use Signal - short of contacting them via some other method and asking for their Signal username, if any. By making the Signal username the same as the user's phone number, I actually DO have a list of Signal 'usernames' on my phone already. As soon as I sign-up, I can send my list of friends' phone numbers to Signal and they can tell me which of those people have Signal accounts.

autoexec 4y ago

> it had to do with not wanting to own the user’s contact list. Using a phone number allowed them to rely on a contact list on the users phone, which is not tied to the signal account. That doesn't make any sense. Signal did the total opposite. It started keeping sensitive user data in the cloud including your name, your photo, your phone number, and a list of your contacts. It stores that data on their servers permanently.

_6hmp 4y ago
I don't think this is true, do you have a source? They store registered users phone numbers and allow discovery by making a request with a hashed version of the phone numbers on your contact list. They add an extra layer to allow attestation of the software doing this using Intel's secure enclave. They give many examples of responding to warrants with only whether the number has been registered and the timestamp of registration, which they explain is the only information they hold. Private Contact Discovery: https://signal.org/blog/private-contact-discovery/ https://signal.org/blog/private-contact-discovery/
- autoexec 4y ago
  Your 2017 blog post is outdated. See: https://community.signalusers.org/t/can-signal-please-update-its-privacy-policy/15323 https://community.signalusers.org/t/can-signal-please-update... and https://community.signalusers.org/t/dont-want-pin-dont-want-anything-stored-in-cloud/14057/27 https://community.signalusers.org/t/dont-want-pin-dont-want-... See here for a discussion on how Intel's 'secure' enclave won't save you: https://community.signalusers.org/t/proper-secure-value-security-pins-are-too-easy-to-brute-force-sgx-is-not-reliable-enough/15096 https://community.signalusers.org/t/proper-secure-value-secu...
  - dcow 4y ago
    There's a horrible conflation of concepts here. A pretty big one. When people talk about cloud services, they generally mean part of an application that runs on the cloud that participates as a trusted actor in the application's trust model. What people in the linked thread are realizing is that "signal has a server" and they are confused because they thought signal didn't have a server, or something. So, what's important about Signals servers is that, outside of initial key exchange which is verified by two parties out of band, they are not a trusted entity, ever. When you send a message it goes through signals servers. When you sync your profile picture with other devices, same thing. The data transits signals servers. This is made possible because of cryptography. By encrypting the data in a way that is indecipherable by 3rd parties (Signal's servers included) your data is isomorphic to random noise. So, the only thing Signal needs to do is route the random noise to the right place. If it doesn't do that, it's a denial of service and about the only attack you're vulnerable to if you use Signal. Otherwise, the receiver gets the exact random noise that you sent, but only they can make sense of it because of the miracle of cryptography. If you're really doing to throw a fit because Signal syncs a profile picture between your devices using the same level of crypto as is used for messaging then you're honestly crazy. No. Signal did not "not have a cloud" and now they "have a cloud". Not by any reasonable interpretation of the events.