Cryptology ePrint Archive: Report 2016/1166

Group key exchange protocols withstanding ephemeral-key reveals

Maria Isabel Gonzalez Vasco and Angel L. Perez del Pozo and Adriana Suarez Corona

Abstract: When a group key exchange protocol is executed, the session key is typically extracted from two types of secrets; long-term keys (for authentication) and freshly generated (often random) values. The leakage of this latter so-called ephemeral keys has been extensively analyzed in the 2-party case, yet very few works are concerned with it in the group setting. We provide a generic {group key exchange} construction that is strongly secure, meaning that the attacker is allowed to learn both long-term and ephemeral keys (but not both from the same participant, as this would trivially disclose the session key). Our design can be seen as a compiler, in the sense that it builds on a 2-party key exchange protocol which is strongly secure and transforms it into a strongly secure group key exchange protocol by adding only one extra round of communication. When applied to an existing 2-party protocol from Bergsma et al., the result is a 2-round group key exchange protocol which is strongly secure in the standard model, thus yielding the first construction with this property.

Category / Keywords: cryptographic protocols / Group Key Agreement, Strong Security, Ephemeral Keys, Compiler

Date: received 20 Dec 2016

Contact author: mariaisabel vasco at urjc es

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Version: 20161228:140726 (All versions of this report)

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