This is a great leap forward in the application of FOSS encryption technologies. Congratulations to the developers, and to the implementors at the Signal Foundation.
Signal Group Calls are one of many features that we have designed with Signal Private Groups as a foundation, using our RingRTC library for handling frame encryption and the logic around setting up and joining calls.
Historically, most anonymous credential schemes enable the credential issuer and credential verifier to be different parties, which is achieved by using complex and costly signature algorithms. These costs are one reason anonymous credentials have seen limited real-world use. However, in Signal’s case the issuer and the verifier would be the same party (the Signal service), which raises the possibility of using more efficient MAC-based keyed-verification anonymous credentials – a concept introduced several years ago by Melissa Chase, Sarah Meiklejohn, and Greg Zaverucha.
It appears that the encryption is based on hardware encoded MAC addresses? Can someone do a breakdown of the paper referenced in the last quoted paragraph? Interested to learn more about this.