Fair Exchange of Short Signatures without Trusted Third Party

Nowadays it is more and more common to trade digital goods on the web: E-books, software licenses, avatar-games currencies like Ultima Online to cite a few. Whether these goods are exchanged on E-bay through Paypal or bought directly to their provider Amazon or Microsoft, the transaction to be secure requires a Trusted Third Party (TTP). The authors propose a protocol to exchange Boneh-Boyen short signatures in a fair way and without relying on a trusted third party. Their protocol is quite practical and is the first of the sort to the best of their knowledge. Their construction uses a new Non-Interactive Zero-Knowledge (NIZK) argument to prove that a commitment is the encryption of a bit vector.