Is a "safely compliant" (semi-)centralized CoinJoin service possible?

[Medusah]

No it doesn't. You can interact with anyone.

You cannot interact with anyone in a coinjoin, and even if you could, it would no longer be trustless.  Let me pose the question again:  If Alice refrains from interacting with any other coinjoin participant, as is typically expected, can she discourage the coordinator from sybil attacking her?  From what I can see, she cannot.  Hence, WabiSabi remains highly susceptible to sybil attacks (launched by the coordinator). 

[tromp]

Are you equating N to the number of servers in each set or is N equal to the amount of organizations?  

One coinswap service is offered by N organizations each employing one server.
Even if 51% of N are colluding, they would learn nothing about any coinswap they choose to complete. The worst that can happen is one server going down and the protocol cannot complete.

Then there could be multiple coinswap services being offered, each with its own set of organizations.

That sounds pretty decentralized to me.

[Kruw]

You cannot interact with anyone in a coinjoin

Yes you can.

[Medusah]

Yes you can.

Top-tier level of argumentation.  You should be proud of yourself. 

[Kruw]

Top-tier level of argumentation.  You should be proud of yourself. 

Thanks, I'm glad I proved that any two people can connect to the same coordinator and verify with each other they are participating in the same round. I don't know how you could possibly reason your way into concluding that anyone can't easily do this.

[Medusah]

Thanks, I'm glad I proved that any two people can connect to the same coordinator and verify with each other they are participating in the same round. I don't know how you could possibly reason your way into concluding that anyone can't easily do this.

Are you seriously contending that in a WabiSabi coinjoin, two parties merging their coins have the required program set up to effectively communicate?  And even if they do and communicate to "ensure" they're not subjected to a sybil attack (lmao, "trust me, I am not attacking you"), it still remains an entirely trustless process.  

As I said, top-tier level of argumentation.  

[Kruw]

Are you seriously contending that in a WabiSabi coinjoin, two parties merging their coins have the required program set up to effectively communicate?

I'm communicating to you using Bitcointalk aren't I? Why would you think that two people communicating with each other is impossible given the fact that we are communicating with each other right now?