alt Hacker News> The server has access to your IP addresses and the server can at will build social graphs about the users.
How could it build a social graph? I think most messages are P2P unless the user activates relaying?
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Discovery is important and a hard problem, worth making some trade-offs for. Signal published a good blog post about this, including this passage:
> In order to turn the address book on a device into a social graph for Signal, the Signal client needs to be able to determine which of the device’s contacts are Signal users. [...] The obvious problem with this method is that the hash of a user identifier can almost always be inverted. [...] This method of contact discovery isn’t ideal because of these shortcomings, but at the very least the Signal service’s design does not depend on knowledge of a user’s social graph in order to function.
Src.: https://signal.org/blog/private-contact-discovery/
edit: Also, Signal is not peer-to-peer. It is a centralized, client-server architecture.
>I think most messages are P2P unless the user activates relaying?
No they're all routed through the servers. It's only the calls that can be sent P2P and you have to opt in for that. The issue is that leaks your IP address to the contact who may not be trustworthy, so it's not used by default.