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The Signal protocol has had "sealed sender" since 2018 - Signal server does not know who sent a message, because the sender's identity is E2E encrypted along wi

by niel 4y ago

The Signal protocol has had "sealed sender" since 2018 - Signal server does not know who sent a message, because the sender's identity is E2E encrypted along with the message. Even if Signal's server saves a message (they claim not to, once downloaded), Signal's server by design has no way of knowing who sent the message.

daneel_w 4y ago
Every inbound message is authenticated, and credentials are stored somewhere. Correct me if I am wrong, but I'm betting that it's with the same credential/channel as for logging-in a user (aka "sender"). Also, wasn't "sealed sender" broken (again) earlier this year by a group of researchers?
- niel 4y ago
  No, sealed sender messages are not authenticated. The sender's client uploads two things: 1) an encrypted message (with sender id encrypted), and 2) a zero-knowledge proof that the sender's client knows the recipient's delivery token. There is no authentication by the sender, and the sender does not upload any credentials.
  - daneel_w 4y ago
    I guess I have to rephrase myself: the API calls are authenticated, because the API endpoints will not consume anonymous requests. I'd be glad if you could point me to documentation proving that the messaging API uses completely different credentials than those for user login, and that the two are also disassociated.
    - melgafin 4y ago
      Good luck finding documentation about the protocols and APIs used by signal. While every random cryptocurrency has a cryptography whitepaper, it seems that Signal does not.
      - niel 4y ago
        Signal published detailed specifications of the protocol with reference implementations since at least Feb 2017 (group messaging protocol was added later on): https://signal.org/docs/ https://signal.org/docs/ The server and clients are open source: https://github.com/signalapp https://github.com/signalapp
    - niel 4y ago
      This doesn't prove anything, but: > Without authenticating, hand the encrypted envelope to the service along with the recipient’s delivery token. Source: https://signal.org/blog/sealed-sender/#:~:text=Without%20authenticating https://signal.org/blog/sealed-sender/#:~:text=Without%20aut... The sender's client sends a certificate derived from the recipient's profile key. This certificate is sent to the server as the header "Unidentified-Access-Key" - you can see how this header is derived from the Signal clients' source. So yes, these API calls are authenticated, but not using the sender's credentials in any way.

by niel 4y ago

daneel_w 4y ago

Every inbound message is authenticated, and credentials are stored somewhere. Correct me if I am wrong, but I'm betting that it's with the same credential/channel as for logging-in a user (aka "sender"). Also, wasn't "sealed sender" broken (again) earlier this year by a group of researchers?

niel 4y ago
No, sealed sender messages are not authenticated. The sender's client uploads two things: 1) an encrypted message (with sender id encrypted), and 2) a zero-knowledge proof that the sender's client knows the recipient's delivery token. There is no authentication by the sender, and the sender does not upload any credentials.
- daneel_w 4y ago
  I guess I have to rephrase myself: the API calls are authenticated, because the API endpoints will not consume anonymous requests. I'd be glad if you could point me to documentation proving that the messaging API uses completely different credentials than those for user login, and that the two are also disassociated.
  - melgafin 4y ago
    Good luck finding documentation about the protocols and APIs used by signal. While every random cryptocurrency has a cryptography whitepaper, it seems that Signal does not.
    - niel 4y ago
      Signal published detailed specifications of the protocol with reference implementations since at least Feb 2017 (group messaging protocol was added later on): https://signal.org/docs/ https://signal.org/docs/ The server and clients are open source: https://github.com/signalapp https://github.com/signalapp
  - niel 4y ago
    This doesn't prove anything, but: > Without authenticating, hand the encrypted envelope to the service along with the recipient’s delivery token. Source: https://signal.org/blog/sealed-sender/#:~:text=Without%20authenticating https://signal.org/blog/sealed-sender/#:~:text=Without%20aut... The sender's client sends a certificate derived from the recipient's profile key. This certificate is sent to the server as the header "Unidentified-Access-Key" - you can see how this header is derived from the Signal clients' source. So yes, these API calls are authenticated, but not using the sender's credentials in any way.