How would a P2P "Collective Transaction" be implemented (to increase privacy) In this thread, Luke Jr mentioned Collective Transactions would be a way for clients to increase anonymity when issuing transactions.


How would such an implementation work?


(Please provide technical details or references as available)
Dark Wallet is probably the closest to actively implementing something along these lines in a client.

See:

https://wiki.unsystem.net/index.php/DarkWallet/Alpha#Mixing


  When sending, the transaction is sent to an internal mixer, that
  starts announcing on the coinjoin channel, if another peer answers,
  both will negotiate a shared transaction that includes both peers
  inputs and outputs. If successful the final transaction will be sent
  into the network.
  
  You can see how a transaction from the mixer looks
  https://blockchain.info/tx/c38aac9910f327700e0f199972eed8ea7c6b1920e965f9cb48a92973e7325046


And also the multisig section that follows:


  Multisig funds are special bitcoin addresses that can be spent from
  only by a number of participants signing the transactions. This means
  accounts can be held among several people or devices, and several
  signatures (above some threshold) will be needed to spend.