Signal has started rolling out Signal Login, an optional registration method that allows users to create a Signal account without providing a phone number. The feature will be rolled out first on Android and will come to iOS later.
As we previously reported, Signal Login is not a free alternative registration method. Signal requires users who choose to register without a phone number to make a one-time payment. The price at launch is $2.99 / € 3.49, although this may vary by region and currency.
Forward secrecy protects against intercepting now and decrypting later when you get access to the users private key: this is only possible on delta chat if you get access to the client database at which point you can read all undeleted messages anyway. (On Signal even deleted messages!)
Or the server(s), no? It’s trivially easy to archive, filter by account, and then decrypt if the one key has been found
Delta chat assumes the relays are evil and of course doesn’t send private keys there