I am trying to come up with what could maybe be a novel algorithm for an application I am writing. Client A has a file fA. Client B has file fB. Each party is untrustworthy and will try to rip off the other party. Client A wants the fB and client B wants fA.
How can I make an algorithm were it is not possible for them to screw the other player.
For example: A encrypts fA and send the file to B. B encrypts fB and sends it to A. Now, both A and B have an encrypted version of the file they want. How can they both share the decryption key at the same time... or what?
Is this even possible? This is breaking my mind.
Since each client will try to rip the other party, Client A cannot send the file fA to client B and expect client B to send back its file. If client A sends it first "with no guarantees", client B will simply run off with the file.
In real life a person holds the pot in one hand, the other holds the cash in the other. They both trade each hand at the same time. The guy with the cash now ends up with the pot and vice versa. How can I do something similar with computer bits. (client A and B are on a network at different locations).
EDIT: Please note that each party has a hash of the file they are supposed to get. Therefore, the parties cannot send a junk file to the other guy whit-out him knowing. A trusted third party will provide the hash.