Motivation Efficient Priced Oblivious Transfer Optimistic Fair POT Optimistic Fair Priced Oblivious Transfer A. Rial B. Preneel Katholieke Universiteit Leuven - ESAT-COSIC IBBT Africacrypt 2010 A. Rial Optimistic Fair POT
Motivation Efficient Priced Oblivious Transfer Optimistic Fair POT Priced Oblivious Transfer: Definition Vendor Buyer ( m 1 , . . . , m N ) , ( p 1 , . . . , p N ) τ ∈ { 1 , . . . , N } ✛ m τ ✲ Properties: V does not learn τ . B does not get any information about other messages. B pays price p τ . A. Rial Optimistic Fair POT
Motivation Efficient Priced Oblivious Transfer Optimistic Fair POT Priced Oblivious Transfer: Definition Vendor Buyer ( m 1 , . . . , m N ) , ( p 1 , . . . , p N ) τ ∈ { 1 , . . . , N } ✛ m τ ✲ Properties: V does not learn τ . B does not get any information about other messages. B pays price p τ . A. Rial Optimistic Fair POT
Motivation Efficient Priced Oblivious Transfer Optimistic Fair POT Priced Oblivious Transfer: Definition Vendor Buyer ( m 1 , . . . , m N ) , ( p 1 , . . . , p N ) τ ∈ { 1 , . . . , N } ✛ m τ ✲ Properties: V does not learn τ . B does not get any information about other messages. B pays price p τ . A. Rial Optimistic Fair POT
Motivation Efficient Priced Oblivious Transfer Optimistic Fair POT Priced Oblivious Transfer: Definition Vendor Buyer ( m 1 , . . . , m N ) , ( p 1 , . . . , p N ) τ ∈ { 1 , . . . , N } ✛ m τ ✲ Properties: V does not learn τ . B does not get any information about other messages. B pays price p τ . A. Rial Optimistic Fair POT
Motivation Efficient Priced Oblivious Transfer Optimistic Fair POT Priced Oblivious Transfer: Construction Vendor Buyer ac 0 ac 0 ✛ Prepaid Mechanism B makes an initial deposit to V . At each purchase, the price is debited from the deposit. V learns neither the price nor the deposit. A. Rial Optimistic Fair POT
Motivation Efficient Priced Oblivious Transfer Optimistic Fair POT Priced Oblivious Transfer: Construction Vendor Buyer ac 0 ac 0 ✛ Prepaid Mechanism B makes an initial deposit to V . At each purchase, the price is debited from the deposit. V learns neither the price nor the deposit. A. Rial Optimistic Fair POT
Motivation Efficient Priced Oblivious Transfer Optimistic Fair POT Priced Oblivious Transfer: Construction Vendor Buyer ac 0 ac 0 ✛ Prepaid Mechanism B makes an initial deposit to V . At each purchase, the price is debited from the deposit. V learns neither the price nor the deposit. A. Rial Optimistic Fair POT
Motivation Efficient Priced Oblivious Transfer Optimistic Fair POT Priced Oblivious Transfer: Construction Vendor Buyer ac 0 ac 0 ✛ Prepaid Mechanism B makes an initial deposit to V . At each purchase, the price is debited from the deposit. V learns neither the price nor the deposit. A. Rial Optimistic Fair POT
Motivation Efficient Priced Oblivious Transfer Optimistic Fair POT Priced Oblivious Transfer: Security Previous Work Half-Simulation secure schemes [AIR01, Tob03]. Vulnerable under attack in [DNO08]. UC-secure scheme [RKP09]. Inefficient. Efficient Full-Simulation Secure POT A. Rial Optimistic Fair POT
Motivation Efficient Priced Oblivious Transfer Optimistic Fair POT Priced Oblivious Transfer: Security Previous Work Half-Simulation secure schemes [AIR01, Tob03]. Vulnerable under attack in [DNO08]. UC-secure scheme [RKP09]. Inefficient. Efficient Full-Simulation Secure POT A. Rial Optimistic Fair POT
Motivation Efficient Priced Oblivious Transfer Optimistic Fair POT Priced Oblivious Transfer: Security Previous Work Half-Simulation secure schemes [AIR01, Tob03]. Vulnerable under attack in [DNO08]. UC-secure scheme [RKP09]. Inefficient. Efficient Full-Simulation Secure POT A. Rial Optimistic Fair POT
Motivation Efficient Priced Oblivious Transfer Optimistic Fair POT Priced Oblivious Transfer: Fairness Previous Work Usually, e-commerce protocols are analyzed to prove their fairness [Kre04]. Non privacy-preserving protocols [EGL85, Gol83]. Privacy-preserving protocols that provide buyers’ anonymity [RR01]. However, no fair POT scheme has been proposed. Malicious V can claim B ran out of funds. Malicious V can deny delivery. Malicious B can falsely accuse an honest V . Fair POT A. Rial Optimistic Fair POT
Motivation Efficient Priced Oblivious Transfer Optimistic Fair POT Priced Oblivious Transfer: Fairness Previous Work Usually, e-commerce protocols are analyzed to prove their fairness [Kre04]. Non privacy-preserving protocols [EGL85, Gol83]. Privacy-preserving protocols that provide buyers’ anonymity [RR01]. However, no fair POT scheme has been proposed. Malicious V can claim B ran out of funds. Malicious V can deny delivery. Malicious B can falsely accuse an honest V . Fair POT A. Rial Optimistic Fair POT
Motivation Efficient Priced Oblivious Transfer Optimistic Fair POT Priced Oblivious Transfer: Fairness Previous Work Usually, e-commerce protocols are analyzed to prove their fairness [Kre04]. Non privacy-preserving protocols [EGL85, Gol83]. Privacy-preserving protocols that provide buyers’ anonymity [RR01]. However, no fair POT scheme has been proposed. Malicious V can claim B ran out of funds. Malicious V can deny delivery. Malicious B can falsely accuse an honest V . Fair POT A. Rial Optimistic Fair POT
Motivation Efficient Priced Oblivious Transfer Optimistic Fair POT Priced Oblivious Transfer: Fairness Previous Work Usually, e-commerce protocols are analyzed to prove their fairness [Kre04]. Non privacy-preserving protocols [EGL85, Gol83]. Privacy-preserving protocols that provide buyers’ anonymity [RR01]. However, no fair POT scheme has been proposed. Malicious V can claim B ran out of funds. Malicious V can deny delivery. Malicious B can falsely accuse an honest V . Fair POT A. Rial Optimistic Fair POT
Motivation Efficient Priced Oblivious Transfer Optimistic Fair POT Priced Oblivious Transfer: Fairness Previous Work Usually, e-commerce protocols are analyzed to prove their fairness [Kre04]. Non privacy-preserving protocols [EGL85, Gol83]. Privacy-preserving protocols that provide buyers’ anonymity [RR01]. However, no fair POT scheme has been proposed. Malicious V can claim B ran out of funds. Malicious V can deny delivery. Malicious B can falsely accuse an honest V . Fair POT A. Rial Optimistic Fair POT
Motivation Efficient Priced Oblivious Transfer Optimistic Fair POT Priced Oblivious Transfer: Fairness Previous Work Usually, e-commerce protocols are analyzed to prove their fairness [Kre04]. Non privacy-preserving protocols [EGL85, Gol83]. Privacy-preserving protocols that provide buyers’ anonymity [RR01]. However, no fair POT scheme has been proposed. Malicious V can claim B ran out of funds. Malicious V can deny delivery. Malicious B can falsely accuse an honest V . Fair POT A. Rial Optimistic Fair POT
Motivation Efficient Priced Oblivious Transfer Optimistic Fair POT Priced Oblivious Transfer: Fairness Previous Work Usually, e-commerce protocols are analyzed to prove their fairness [Kre04]. Non privacy-preserving protocols [EGL85, Gol83]. Privacy-preserving protocols that provide buyers’ anonymity [RR01]. However, no fair POT scheme has been proposed. Malicious V can claim B ran out of funds. Malicious V can deny delivery. Malicious B can falsely accuse an honest V . Fair POT A. Rial Optimistic Fair POT
Motivation Efficient Priced Oblivious Transfer Optimistic Fair POT Priced Oblivious Transfer: Fairness Previous Work Usually, e-commerce protocols are analyzed to prove their fairness [Kre04]. Non privacy-preserving protocols [EGL85, Gol83]. Privacy-preserving protocols that provide buyers’ anonymity [RR01]. However, no fair POT scheme has been proposed. Malicious V can claim B ran out of funds. Malicious V can deny delivery. Malicious B can falsely accuse an honest V . Fair POT A. Rial Optimistic Fair POT
Motivation Efficient Priced Oblivious Transfer Optimistic Fair POT Outline Efficient Priced Oblivious Transfer 1 Construction Comparison with Previous Work Optimistic Fair POT 2 Definition Construction A. Rial Optimistic Fair POT
Motivation Construction Efficient Priced Oblivious Transfer Comparison with Previous Work Optimistic Fair POT Outline Efficient Priced Oblivious Transfer 1 Construction Comparison with Previous Work Optimistic Fair POT 2 Definition Construction A. Rial Optimistic Fair POT
Motivation Construction Efficient Priced Oblivious Transfer Comparison with Previous Work Optimistic Fair POT Outline Efficient Priced Oblivious Transfer 1 Construction Comparison with Previous Work Optimistic Fair POT 2 Definition Construction A. Rial Optimistic Fair POT
Motivation Construction Efficient Priced Oblivious Transfer Comparison with Previous Work Optimistic Fair POT Overview Our POT scheme is based on the OT scheme of [CNS07] and thus follows an assisted decryption approach. Generic POT scheme V (( m i , p i ) N i = 1 ) Initialization B ( ac 0 ) ( C 1 , . . . , C N ) ✲ sk , ∀ i , C i = POTInitV ( m i , p i ) Verify ( C 1 , . . . , C N ) ( ac 0 ) ac 0 ac 0 ✛ V Transfer B ( τ ) ( Q ) POTVerReq ( Q ) ( Q , Qpriv ) = POTReq ( C τ ) ✛ ( R ) R = POTResp ( Q , sk ) POTVerResp ( R ) ✲ ( m τ ) = POTComplete ( R , Qpriv ) A. Rial Optimistic Fair POT
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