It is terribly chatty for me. I'd like to check if my quick glance takeaways are correct:
1. First you identify a traditional mixing service's transactions.
2. Then you mess around with the possible timeframes for the mixes.
3. Finally you do a subset-sum analysis. (Amount based analysis of mixing inputs and outputs.)
Thus you get most of the links between incoming and outgoing transactions, except those that happen to be equal within the appropriate mixing window.
Is this a fair way to describe what you did?
Yes, you could define it like that. But generally speaking there are only two big steps:
1) Identify mixing service transactions within blockchain data
2) Find an algorithm to connect input transactions to output transactions
The method of solving each steps is based on the implementation of the mixing service.
In case of coinmixer.se the first step could be solved by analyzing transaction data and the second step could be solved by analyzing the transaction flow and transaction data.
In case of bitmixer.io both steps could be solved by analyzing transaction data - no transaction flow is needed here.
I'm curious if this methods would work with CoinJoin transactions, particularly with those wallets were there aren't many users (I guess that means all).
There is a lot of interest in this topic. I will definitely also look into decentralized mixing protocol implementations. However, I will focus in my next work on chipmixer.com and some privacy enhancing coins (dash, monero, zcash) as this seems a very challenging and interesting task.
What kind of attacks did you exactly make? I'm keen to know them and understand all of them in a much better way if you could elaborate it well. Also, how can you consider the mentioned mixer services to be centralized?
You may find it stupid but I wish to ask one more question here, that when you're able to attack these services (don't know exactly the type of attack, but still a query in my mind), weren't you able to fetch transactions done by XMR and Dash users? It'd be a threat to these alts if you or any dev will be able to fetch the real transactions among the mixed ones as well as I believe you already are a fear to all of us who use these services because if this is actually true, what's the meaning for anyone to use a mixer?
Mixing Services work like black boxes. You put your coins in, some "magic" happens and you receive anonymized coins. Since Bitcoin is purely transparent and you are able to to analyze each transaction in blockchain space you have enough data to identify and deanomyize transactions regarding the mixing service. You just have to filter all blockchain data which is not interesting for you and analyze the rest.
These services are purely centralized, since you send your coins to a centralized party. If the mixing service wants to steal your coins - they definitely are able to do this. Just remember: whenever you lose the control over your coins and some party is able to steal your coins - it is a centralized service.
In decentralized mixing/tumbling no centralized party is able to steal your coins.
I did not look into the specific implementation of dash, monero, zcash. General speaking the difference between mentioned cryptos and bitcoin is, that bitcoin is not meant to provide privacy while the main focus of monero and zcash is privacy. They are built in a way to provide privacy, while in bitcoin some services try to implement algorithms to provide privacy on a cryptocurrency which is not meant to guarantee privacy.