EasyUC: using EasyCrypt to mechanize proofs of universally composable security

We present a methodology for using the EasyCrypt proof assistant (originally designed for mechanizing the generation of proofs of game-based security of cryptographic schemes and protocols) to mechanize proofs of security of cryptographic protocols within the universally composable (UC) security framework. This allows, for the first time, the mechanization and formal verification of the entire sequence of steps needed for proving simulation-based security in a modular way: Specifying a protocol and the desired ideal functionality; Constructing a simulator and demonstrating its validity, via reduction to hard computational problems; Invoking the universal composition operation and demonstrating that it indeed preserves security. We demonstrate our methodology on a simple example: stating and proving the security of secure message communication via a one-time pad, where the key comes from a Diffie-Hellman key-exchange, assuming ideally authenticated communication. We first put together EasyCrypt-verified proofs that: (a) the Diffie-Hellman protocol UC-realizes an ideal key-exchange functionality, assuming hardness of the Decisional Diffie-Hellman problem, and (b) one-time-pad encryption, with a key obtained using ideal key-exchange, UC-realizes an ideal secure-communication functionality. We then mechanically combine the two proofs into an EasyCrypt-verified proof that the composed protocol realizes the same ideal secure-communication functionality. Although formulating a methodology that is both sound and workable has proven to be a complex task, we are hopeful that it will prove to be the basis for mechanized UC security analyses for significantly more complex protocols and tasks.Accepted manuscrip

Universal Composability is Secure Compilation

Universal composability is a framework for the specification and analysis of cryptographic protocols with a strong compositionality guarantee: UC protocols are secure even when composed with other protocols. Secure compilation tells whether compiled programs are as secure as their source-level counterparts, no matter what target-level code they interact with. These two disciplines are studied in isolation, but we believe there is a deeper connection between them with benefits from both worlds to reap. This paper outlines the connection between universal composability and robust compilation, the latest of secure compilation theories. We show how to read the universal composability theorem in terms of a robust compilation theorem and vice-versa. This, in turn, shows which elements of one theory corresponds to which element in the other theory. We believe this is the first step towards understanding how can secure compilation theories be used in universal composability settings and vice-versa

Universally Composable Security Analysis of TLS---Secure Sessions with Handshake and Record Layer Protocols

We present a security analysis of the complete TLS protocol in the Universal Composable security framework. This analysis evaluates the composition of key exchange functionalities realized by the TLS handshake with the message transmission of the TLS record layer to emulate secure communication sessions and is based on the adaption of the secure channel model from Canetti and Krawczyk to the setting where peer identities are not necessarily known prior the protocol invocation and may remain undisclosed. Our analysis shows that TLS, including the Diffie-Hellman and key transport suites in the uni-directional and bi-directional models of authentication, securely emulates secure communication sessions

Public Evidence from Secret Ballots

Elections seem simple---aren't they just counting? But they have a unique, challenging combination of security and privacy requirements. The stakes are high; the context is adversarial; the electorate needs to be convinced that the results are correct; and the secrecy of the ballot must be ensured. And they have practical constraints: time is of the essence, and voting systems need to be affordable and maintainable, and usable by voters, election officials, and pollworkers. It is thus not surprising that voting is a rich research area spanning theory, applied cryptography, practical systems analysis, usable security, and statistics. Election integrity involves two key concepts: convincing evidence that outcomes are correct and privacy, which amounts to convincing assurance that there is no evidence about how any given person voted. These are obviously in tension. We examine how current systems walk this tightrope.Comment: To appear in E-Vote-Id '1

Universally composable end-to-end secure messaging

CNS-1718135 - National Science Foundation; CNS-1801564 - National Science Foundation; CNS-1931714 - National Science Foundation; CNS-1915763 - National Science Foundation; HR00112020021 - Department of Defense/DARPA; 000000000000000000000000000000000000000000000000000000037211 - SRI Internationalhttps://eprint.iacr.org/2022/376.pdfAccepted manuscrip

A Blockchain-based Decentralized, Fair and Authenticated Information Sharing Scheme in Zero Trust Internet-of-Things

This is the author accepted manuscript. The final version is available from IEEE via the DOI in this recordData availability statement: The [code] data used to support the findings of this study have been deposited in the [IEEE DATAPORT] repository ([10.21227/rtmq-t937]).Internet-of-Things (IoT) are increasingly operating in the zero-trust environments where any devices and systems may be compromised and hence untrusted. In addition, data collected by and sent from IoT devices may be shared with edge computing systems in order to reduce the reliance on centralized (cloud) servers, leading to further security and privacy issues. To cope with these challenges, this paper proposes an innovative blockchain-enabled information sharing solution in zero-trust context to guarantee anonymity yet entity authentication, data privacy yet data trustworthiness, and participant stimulation yet fairness. This new solution is able to support filtering of fabricated information through smart contracts, effective voting, and consensus mechanisms, which can prevent unauthenticated participants from sharing garbage information. We also prove the proposed solution is secure in the universal composability framework, and further evaluate its performance over an ETH-based platform to demonstrate its utility.Foundation of Yunnan Key Laboratory of Blockchain Application TechnologyNational Natural Science Foundation of ChinaProvincial Key Research and Development Program of HubeiFoundation of Henan Key Laboratory of Network Cryptography TechnologyFoundation of Hubei Key Laboratory of Intelligent Geo-Information Processin

Proving the TLS Handshake Secure (As It Is)

International audienceThe TLS Internet Standard features a mixed bag of cryptographic algorithms and constructions, letting clients and servers negotiate their use for each run of the handshake. Although many ciphersuites are now well-understood in isolation, their composition remains problematic, and yet it is critical to obtain practical security guarantees for TLS, as all mainstream implementations support multiple related runs of the handshake and share keys between algorithms.We study the provable security of the TLS handshake, as it is implemented and deployed. To capture the details of the standard and its main extensions, we rely on miTLS, a verified reference implementation of the protocol. We propose new agile security definitions and assumptions for the signatures, key encapsulation mechanisms (KEM), and key derivation algorithms used by the TLS handshake. To validate our model of key encapsulation, we prove that both RSA and Diffie-Hellman ciphersuites satisfy our definition for the KEM. In particular, we formalize the use of PKCS#1v1.5 and build a 3,000-line EasyCrypt proof of the security of the resulting KEM against replayable chosen-ciphertext attacks under the assumption that ciphertexts are hard to re-randomize.Based on our new agile definitions, we construct a modular proof of security for the miTLS reference implementation of the handshake, including ciphersuite negotiation, key exchange, renegotiation, and resumption, treated as a detailed 3,600-line executable model. We present our main definitions, constructions, and proofs for an abstract model of the protocol, featuring series of related runs of the handshake with different ciphersuites. We also describe its refinement to account for the whole reference implementation, based on automated verification tools

Universally Composable Authentication and Key-exchange with Global PKI

Message authentication and key exchange are two of the most basic tasks of cryptography. Solutions based on public-key infrastructure (PKI) are prevalent. Still, the state of the art in composable security analysis of PKI-based authentication and key exchange is somewhat unsatisfactory. Specifically, existing treatments either (a)~make the unrealistic assumption that the PKI is accessible only within the confines of the protocol itself, thus failing to capture real-world PKI-based authentication, or (b)~impose often-unnecessary requirements---such as strong on-line non-transferability---on candidate protocols, thus ruling out natural candidates. We give a modular and universally composable analytical framework for PKI-based message authentication and key exchange protocols. This framework guarantees security even when the PKI is pre-existing and globally available, without being unnecessarily restrictive. Specifically, we model PKI as a global set-up functionality within the \emph{Global~UC} security model [Canetti \etal, TCC 2007] and relax the ideal authentication and key exchange functionalities accordingly. We then demonstrate the security of basic signature-based authentication and key exchange protocols. Our modeling makes minimal security assumptions on the PKI in use; in particular, ``knowledge of the secret key\u27\u27 is not needed

Applying Secure Multi-party Computation in Practice

In this work, we present solutions for technical difficulties in deploying secure multi-party computation in real-world applications. We will first give a brief overview of the current state of the art, bring out several shortcomings and address them. The main contribution of this work is an end-to-end process description of deploying secure multi-party computation for the first large-scale registry-based statistical study on linked databases. Involving large stakeholders like government institutions introduces also some non-technical requirements like signing contracts and negotiating with the Data Protection Agency