if I use CounJoin on blockchain.info, where I have one input and one output
If you only have one input, you're not joining any coins. The point is mixing unspent outputs from several people/addresses so external observers can't figure out where each output has gone.
I understand, but if we have 3 people, I put in 5BTC, someone else puts in 2BTC, and the third person puts in 3.5BTC, the coins all get broken up into random amounts and go through two stage mix, in the end, we still have 5BTC, 2BTC, and 3.5BTC, just in new addresses. Isn't that fairly easy to track?
I know I'm missing something... What is it?The possibility that you could get 5 BTC sent to more than one address. Also, you could use the system to pay people too. So, you get your 5 BTC sent to 4 adddresess that belong to you, and the small fraction you are paying to someone else goes to their address. To the outside observer, do all 5 addresses belong to the original holder? Do they all belong to someone receiving a total of 5 BTC from the original holder? Or somewhere inbetween? Impossible to tell, and so analysing the transaction leaves you with lots of questions and no answers.