@minnmann, I also was in the @sgergely dilemma.

If connection is performed from user’s Signal client:

ISP knows what (if non-encrypted) and from whom the link preview is,

targeted server knows who (from user’s IP) and what (content) is linked.

If connection is performed from proxy Signal service:

ISP knows that user is using Signal service (because target IP is Signal server),

Signal service know you have executed link preview from particular web site,

targeted server known that request was executed from Signal server and know the content of message.

I really like this idea. ISP, Signal service and targeted server no one knows all the data to track them and so invade the privacy. The only one that knows all the data is user itself. Brilliant idea.

The other idea to even more hide the link preview would be to use Tor network, but in this case I am afraid it would slow down the response, that most of the users do not want. We need to balance the best possible security/privacy vs. convenience. When both criteria are reasonable met, then we are at the right track of solution.

I also like the idea that http links (non encrypted) do not have a preview. This would reveal the privacy data to Signal service. Developers do not want to have any kind of personal data.

As always, Signal rocks with protecting end-users privacy. Love it.