?url_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Adc&rft.title=Recurring+Contingent+Payment+for+Proofs+of+Retrievability&rft.creator=Abadi%2C+Aydin&rft.creator=Murdoch%2C+steven&rft.creator=Zacharias%2C+Thomas&rft.description=Fair+exchange+protocols+let+two+mutually+distrusted+parties+exchange+digital+data+in+a+way+that+neither+can+cheat.+At+CCS+2017%2C+Campanelli+et+al.+proposed+two+blockchain-based+protocols+for+the+fair+exchange+of+digital+coins+and+a+certain+service%2C+i.e.%2C+%E2%80%9Cproofs+of+retrievability%E2%80%9D+(PoR)%2C+that+take+place+between+a+buyer+and+seller.+In+this+work%2C+we+identify+two+serious+issues+of+these+schemes%3B+namely%2C+(1)+a+malicious+client+can+waste+the+seller%E2%80%99s+resources%2C+and+(2)+real-time+leakage+of+information+to+non-participants+in+the+exchange.+To+rectify+the+issues%2C+we+propose+a+%E2%80%9Crecurring+contingent+PoR+payment%E2%80%9D+(RC-PoR-P).+It+lets+the+fair+exchange+reoccur+while+ensuring+that+the+seller%E2%80%99s+resources+are+not+wasted%2C+and+the+parties%E2%80%99+privacy+is+preserved.+We+implemented+the+RC-+PoR-P.+Our+cost+analysis+indicates+that+the+RC-PoR-P+is+efficient.+The+RC-PoR-P+is+the+first+of+its+kind+that+offers+all+the+above+features.&rft.subject=Cryptographic+protocol%2C+blockchain%2C+smart+contracts%2C+fair+exchange&rft.publisher=Cryptology+ePrint+Archive&rft.date=2021-09-10&rft.type=Report&rft.language=eng&rft.source=++++(Paper+2021%2F1145+++).+Cryptology+ePrint+Archive+++++&rft.format=text&rft.identifier=https%3A%2F%2Fdiscovery.ucl.ac.uk%2Fid%2Feprint%2F10153741%2F1%2F2021-1145.pdf&rft.identifier=https%3A%2F%2Fdiscovery.ucl.ac.uk%2Fid%2Feprint%2F10153741%2F&rft.rights=open