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ORBi

"The Simplest Protocol for Oblivious Transfer'' Revisited Genç, Ziya Alper ; ; Rial, Alfredo in Information Processing Letters (2020) In 2015, Chou and Orlandi presented an oblivious transfer protocol that already drew a lot of attention both from theorists and practitioners due to its extreme simplicity and high efficiency. Chou and ... [more ▼] In 2015, Chou and Orlandi presented an oblivious transfer protocol that already drew a lot of attention both from theorists and practitioners due to its extreme simplicity and high efficiency. Chou and Orlandi claimed that their protocol is universally composable secure (UC-secure) in the random oracle model under dynamic corruptions. UC-security is a very strong security guarantee that assures that, not only the protocol in itself is secure, but can be also used safely in larger protocols. Unfortunately, in this work we point out a flaw in their security proof for the case of a corrupt sender. In more detail, we define a decisional problem and we prove that, if a correct security proof for the Chou and Orlandi's protocol is provided, then this problem can be solved correctly with overwhelming probability. Therefore, the protocol of Chou and Orlandi cannot be instantiated securely with groups for which our decisional problem cannot be solved correctly with overwhelming probability. Consequently, the protocol of Chou and Orlandi cannot be instantiated with {\em all} groups $\G$ in which the CDH problem is intractable, but only with groups in which both the CDH problem is intractable and our decisional problem can be solved with overwhelming probability. After the appearance of our work, Chou and Orlandi acknowledged the problems we pointed out in their security proof and subsequent works showed additional issues, removing the claims of UC security of their protocol. [less ▲] Detailed reference viewed: 113 (6 UL)A conditional access system with revocation for mobile pay-TV systems revisited Rial, Alfredo in Information Processing Letters (2019), 147 Detailed reference viewed: 129 (4 UL)Issuer-Free Oblivious Transfer with Access Control Revisited Rial, Alfredo in Information Processing Letters (2017) Oblivious transfer with access control (OTAC) is an extension of oblivious transfer where each message is associated with an access control policy. A receiver can obtain a message only if her attributes ... [more ▼] Oblivious transfer with access control (OTAC) is an extension of oblivious transfer where each message is associated with an access control policy. A receiver can obtain a message only if her attributes satisfy the access control policy for that message. In most schemes, the receiver's attributes are certified by an issuer. Recently, two Issuer-Free OTAC protocols have been proposed. We show that the security definition for Issuer-Free OTAC fulfilled by those schemes poses a problem. Namely, the sender is not able to attest whether a receiver possesses a claimed attribute. Because of this problem, in both Issuer-Free OTAC protocols, any malicious receiver can obtain any message from the sender, regardless of the access control policy associated with the message. To address this problem, we propose a new security definition for Issuer-Free OTAC. Our definition requires the receiver to prove in zero-knowledge to the sender that her attributes fulfill some predicates. Our definition is suitable for settings with multiple issuers because it allows the design of OTAC protocols where the receiver, when accessing a record, can hide the identity of the issuer that certified her attributes. [less ▲] Detailed reference viewed: 129 (14 UL)Limits of a conjecture on a leakage-resilient cryptosystem Galindo, David ; Venkatesh, Srinivas Vivek in Information Processing Letters (2014), 114(4), 192-196 Recently it was conjectured that an ElGamal-based public-key encryption scheme with stateful decryption resists lunch-time chosen ciphertext and leakage attacks in the only computation leaks information ... [more ▼] Recently it was conjectured that an ElGamal-based public-key encryption scheme with stateful decryption resists lunch-time chosen ciphertext and leakage attacks in the only computation leaks information model. We give a non-trivial upper bound on the amount of leakage tolerated by this conjecture. More precisely, we prove that the conjecture does not hold if more than a (3/8 + o (1)) fraction of the bits are leaked at every decryption step, by showing a lunch-time attack that recovers the full secret key. The attack uses a new variant of the Hidden Number Problem, that we call Hidden Shares – Hidden Number Problem, which is of independent interest. [less ▲] Detailed reference viewed: 144 (2 UL)Fast leader election in anonymous rings with bounded expected delay ; ; et al in Information Processing Letters (2011), 111(17), 864-870 Detailed reference viewed: 97 (2 UL)Connecting face hitting sets in planar graphs ; Schweitzer, Patrick in Information Processing Letters (2010), 111(1), 11-15 We show that any face hitting set of size n of a connected planar graph with a minimum degree of at least 3 is contained in a connected subgraph of size 5n−6. Furthermore we show that this bound is tight ... [more ▼] We show that any face hitting set of size n of a connected planar graph with a minimum degree of at least 3 is contained in a connected subgraph of size 5n−6. Furthermore we show that this bound is tight by providing a lower bound in the form of a family of graphs. This improves the previously known upper and lower bound of 11n−18 and 3n respectively by Grigoriev and Sitters. Our proof is valid for simple graphs with loops and generalizes to graphs embedded in surfaces of arbitrary genus. [less ▲] Detailed reference viewed: 110 (2 UL)On a new formal proof model for RFID location privacy van Deursen, Ton ; Radomirovic, Sasa in Information Processing Letters (2009), 110(2), 57-61 Detailed reference viewed: 88 (0 UL)Generating anomalous elliptic curves Leprévost, Franck ; ; Varrette, Sébastien et al in Information Processing Letters (2005), 93 Detailed reference viewed: 149 (2 UL) |
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