As we all know by now, bitcoin is not really anonymous (though I agree it's close). But Zerocoin is. And Zerocoin will kill bitcoin, you mark my words.
Excerpts from a blog on Zerocoin below from The Economist. See link for full article.
TonyT
http://www.economist.com/blogs/babbage/2014/01/cryptographic-currency Babbage
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Cryptographic currency
Washing virtual money
Jan 26th 2014, 15:55 by G.F. | SEATTLE
MATT Green would like you to think of Zerocoin, a Bitcoin-like alternative currency in the process of finalising its specifications, as a bulletin board in a shared space—like an office tea room. Pin a ten-pound note to the board and you may later remove any other similar note from the board so long as you can prove that you pinned a like amount at any previous time. Such a pool of cash would launder a transaction, disconnecting the serial number on the note you pinned from the one you claimed.
Bitcoin was designed, in part, to ensure complete and permanent transparency about each transfer of value from one party to another, while uncoupling it largely from the concept of an independent identity. Researchers have shown it is possible in many circumstances with the current version of the common Bitcoin software code, widely used on servers and client software, to track transactions well enough to group them by the parties engaged. Tie that to an exchange, which converts legal tender to and from Bitcoins, or a wallet service, which stores the coins on behalf of members, and external authorities could issue warrants and finger individuals.
Dr Green and three colleagues at Johns Hopkins University—Christina Garman, Ian Miers, and Aviel D. Rubin—released a paper in April 2013 that charted a different path relying on zero-knowledge proofs (ZKP). In Zerocoin, originally proposed as an extension to Bitcoin that could be incorporated into the currency's basic protocols, a Zerocoin is minted by a party who creates a unique serial number for a coin and then generates a random number. The two numbers are combined with a cryptographic function called hashing that is effectively impossible to reverse: only the possessor of the serial number and random number can produce the resulting hash.
Dr Green explains that this proof gives no insight to other parties as to which coin is possessed by the owner even though the serial number has been revealed. The random number remains private and cannot be deduced. But because the owner knows it, the ZKP provides full assurance to the rest of the currency ecosystem of that ownership as all other parties can duplicate the ZKP without knowledge of that secret number. "We are proving to you that we are talking about something that is in the set of previous transactions," says Dr Green.
Dr Green says he has no particular political agenda for Zerocoin. Instead, it's the academic delight of perfecting a system which takes Bitcoin's pseudo-anonymity into something approaching full anonymity. His group wants to sort out now how to fairly administer the early generation of coins and the like, but "if people want to go a different direction with it after it's out there, that's fine." Once the genie is out of the bottle, Dr Green doesn't plan to retain the stopper.