Nomen Nescio wrote:

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Bin laden demolitions has authorised me to offer you a once in a lifetime deal. 1million dollars untracable digital cash will be paid to an account/s of your choice for enough intelligence to proceed with further superpower implosions. Insider info preffered but not essential,leave packet online in freenet transient node...

Is there any way to solve this transaction problem without a mutually-trusted third party?

It would be necessary to reduce the criteria used by the purchaser into algorithmic form. Write a program which would take the data and produce a yes/no answer. The program has to be such that even if the seller knows the program, he can't produce fake data which would fool the program.

Then the seller can commit to his data and produce a zero-knowledge proof that the committed data satisfies the criteria in the program. This can be done reasonably efficiently for moderate sized programs. It will leak no information about the data other than the yes/no answer from the program.

But BLD would still be able to cheat the seller, wouldn't they? The account number might be valid but unfunded, or any variation on that. I'm looking for a way for each party to be sure he gets what he wants, with no trusted third party and no recourse to government. -- Steve Furlong Computer Condottiere Have GNU, Will Travel 617-670-3793 "Good people do not need laws to tell them to act responsibly while bad people will find a way around the laws." -- Plato