The group for anonymous communication in Dissent is formed using unspecified means. It could be everybody who signed up in the last month, obtained a credential from some authority, has a key within the web of trust for the group, etc.
Some of these methods obviously allow the adversary to create Sybils (aka sockpuppets). The ones that don't may not provide anonymity about who is in the group, but the protocol will provide anonymity for who said what during the group communication. This is still extremely valuable. Consider voting as an example: the group is known, but individual vote anonymity matters.
If the group formation mechanism does allow Sybils, that still doesn't violate anonymity. For a message from an honest member, the adversary cannot tell which honest member it came from. It also doesn't violate the accountability of the protocol - any disruption will be attributable to some Sybil, who will be punished.
I think it's unfortunate that the page mentions that Dissent protects groups against Sybils and sockpuppets. I too spend lots of time going trough these papers looking up what the algorithm was. Dissent clearly does not even try to solve Sybil/sockpuppet problem.
1. Anonymity is provided as long as there is a single trustworthy member, regardless of how many phony members there are.
2. Denial-of-service resistance is provided even against many Sybils - eventually they will all be kicked out of the group and communication can proceed.
This is in contrast to protocols (e.g. onion routing, Aqua[0]) that only provide their security properties when the adversary doesn't control too much of the system. I think it is a fair claim to make and in particular is clear to people familiar with this area of research.
You seem to be outsourcing the trust mechanism to the users, while the page implies that you've solved the trust problem internally through the protocol.
Don't get me wrong, the research is very impressive in it's own right, but that's at best misleading.
What is the mechanism to kick Sybils out of the group, though? How is it ensured that enough sockpuppets don't try to kick trustworthy groups out? I am not following the mechanisms here.
The group for anonymous communication in Dissent is formed using unspecified means. It could be everybody who signed up in the last month, obtained a credential from some authority, has a key within the web of trust for the group, etc.
Some of these methods obviously allow the adversary to create Sybils (aka sockpuppets). The ones that don't may not provide anonymity about who is in the group, but the protocol will provide anonymity for who said what during the group communication. This is still extremely valuable. Consider voting as an example: the group is known, but individual vote anonymity matters.
If the group formation mechanism does allow Sybils, that still doesn't violate anonymity. For a message from an honest member, the adversary cannot tell which honest member it came from. It also doesn't violate the accountability of the protocol - any disruption will be attributable to some Sybil, who will be punished.