A Framework for the Study of Cryptographic Protocols

Carsten Baum, Bernardo David, Rafael Dowsley

Richard A. DeMillo, Nancy Ann Lynch, Michael Merritt

Ran Canetti

We present a general framework for representing cryptographic protocols and analyzing their security. The framework allows specifying the security requirements of practically any cryptographic task in a unified and systematic way. Furthermore, in this framework the security of protocols is preserved under a general protocol composition operation, called universal composition. The proposed framework with its security-preserving composition operation allows for modular design and analysis of complex cryptographic protocols from relatively simple building blocks. Moreover, within this framework, protocols are guaranteed to maintain their security in any context, even in the presence of an unbounded number of arbitrary protocol instances that run concurrently in an adversarially controlled manner. This is a useful guarantee, that allows arguing about the security of cryptographic protocols in complex and unpredictable environments such as modern communication networks.

Ling Dong, Kefei Chen

Ran Canetti

This work presents a general framework for describing cryptographic protocols and analyzing their security. The framework allows specifying the security requirements of practically any cryptographic task in a unified and systematic way. Furthermore, in this framework the security of protocols is preserved under a general composition operation, called universal composition. The proposed framework with its security-preserving composition operation allows for modular design and analysis of complex cryptographic protocols from simpler building blocks. Moreover, within this framework, protocols are guaranteed to maintain their security in any context, even in the presence of an unbounded number of arbitrary protocol sessions that run concurrently in an adversarially controlled manner. This is a useful guarantee, which allows arguing about the security of cryptographic protocols in complex and unpredictable environments such as modern communication networks.

Lea Kissner, Dávid Molnár

Many cryptographic protocols secure against malicious players use specially designed cryptographic tools. Essentially, these special tools function much like less-expensive tools, but give extra ‘powers’ to a reduction or simulation algorithm. Using these powers, cryptographers can construct a proof of security using standard techniques. However, these powers are not available to either the honest parties or the adversary. In a large class of protocols, by replacing the expensive, specially designed cryptographic tool with a corresponding less-expensive tool, we can improve the protocol’s efficiency without changing the functionality available to either the adversary or the honest parties. The key motivating question we address in this paper is whether the new, ‘substituted’ protocol is still secure. We introduce a framework for reasoning about this question. Our framework uses translators: special purpose oracles that map outputs of one cryptographic tool to corresponding outputs of a different tool. Translators are similar to, but generally weaker than, the “angels” of Prabhakaran and Sahai [29]. We introduce the notion of substitution-friendly protocols and show that such protocols remain secure after substitution in our framework. We also leverage existing proofs of security; there is no need to re-prove security from scratch. We demonstrate our framework with a non-interactive non-malleable bit commitment protocol.