Welcome to the resource topic for 2024/324
Title:
Under What Conditions Is Encrypted Key Exchange Actually Secure?
Authors: Jake Januzelli, Lawrence Roy, Jiayu Xu
Abstract:A Password-Authenticated Key Exchange (PAKE) protocol allows two parties to agree upon a cryptographic key, in the setting where the only secret shared in advance is a low-entropy password. The standard security notion for PAKE is in the Universal Composability (UC) framework. In recent years there have been a large number of works analyzing the UC-security of Encrypted Key Exchange (EKE), the very first PAKE protocol, and its One-encryption variant (OEKE), both of which compile an unauthenticated Key Agreement (KA) protocol into a PAKE.
In this work, we present a comprehensive and thorough study of the UC-security of both EKE and OEKE in the most general setting and using the most efficient building blocks:
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We show that among the seven existing results on the UC-security of (O)EKE, six are flawed;
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We show that for (O)EKE to be UC-secure, the underlying KA protocol needs to satisfy the properties of strong pseudorandomness, pseudorandom non-malleability, and collision resistance, all of which are missing in existing works;
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We give UC-security proofs for EKE and OEKE using Programmable-Once Random Function (POPF), which is the most efficient instantiation to date and is around 4 times faster than the standard instantiation using Ideal Cipher (IC).
Our results in particular allow for PAKE constructions from post-quantum KA protocols such as Kyber. We also give a security analysis of POPF in a new composition framework called almost UC, which we believe is interesting in its own right.
ePrint: https://eprint.iacr.org/2024/324
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