AMC
Another look at generic groups
Neal Koblitz Alfred Menezes
Starting with Shoup's seminal paper [24], the generic group model has been an important tool in reductionist security arguments. After an informal explanation of this model and Shoup's theorem, we discuss the danger of flaws in proofs. We next describe an ontological difference between the generic group assumption and the random oracle model for hash unctions. We then examine some criticisms that have been leveled at the generic group model and raise some questions of our own.
keywords: Cryptography generic group. public key
AMC
Another look at security definitions
Neal Koblitz Alfred Menezes
We take a critical look at security models that are often used to give "provable security" guarantees. We pay particular attention to digital signatures, symmetric-key encryption, and leakage resilience. We find that there has been a surprising amount of uncertainty about what the "right" definitions might be. Even when definitions have an appealing logical elegance and nicely reflect certain notions of security, they fail to take into account many types of attacks and do not provide a comprehensive model of adversarial behavior.
keywords: provable security Cryptography definitions.
AMC
Generalizations of Verheul's theorem to asymmetric pairings
Koray Karabina Edward Knapp Alfred Menezes
For symmetric pairings $e : \mathbb{G} \times \mathbb{G} \rightarrow \mathbb{G}_T$, Verheul proved that the existence of an efficiently-computable isomorphism $\phi : \mathbb{G}_T \rightarrow \mathbb{G}$ implies that the Diffie-Hellman problems in $\mathbb{G}$ and $\mathbb{G}_T$ can be efficiently solved. In this paper, we explore the implications of the existence of efficiently-computable isomorphisms $\phi_1 : \mathbb{G}_T \rightarrow \mathbb{G}_1$ and $\phi_2 : \mathbb{G}_T \rightarrow \mathbb{G}_2$ for asymmetric pairings $e : \mathbb{G}_1 \times \mathbb{G}_2 \rightarrow \mathbb{G}_T$. We also give a simplified proof of Verheul's theorem.
keywords: cryptography discrete logarithm problem. asymmetric pairings Verheul's theorem

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