Automated verification of equivalence properties of cryptographic protocols

The original publication is available at www.springerlink.comInternational audienceIndistinguishability properties are essential in formal verification of cryptographic protocols. They are needed to model anonymity of cryptographic protocols. They are needed to model anonymity properties, strong versions of confidentiality and resistance to offline guessing attacks, and can be conveniently modeled using process equivalences. We present a novel procedure to verify equivalence properties for bounded number of sessions. Our procedure is able to verify trace equivalence for determinate cryptographic protocols. On determinate protocols, trace equivalence coincides with observational equivalence which can therefore be automatically verified for such processes. When protocols are not determinate our procedure can be used for both under- and over-approximations of trace equivalence, which proved successful on examples. The procedure can handle a large set of cryptographic primitives, namely those which can be modeled by an optimally reducing convergent rewrite system. Although, we were unable to prove its termination, it has been implemented in a prototype tool and has been effectively tested on examples, some of which were outside the scope of existing tools

Automated Verification of Equivalence Properties of Cryptographic Protocols

Indistinguishability properties are essential in formal verification of cryptographic protocols. They are needed to model anonymity properties, strong versions of confidentiality and resistance against offline guessing attacks, which can be conveniently modeled using process equivalences. We present a novel procedure to verify equivalence properties for a bounded number of sessions of cryptographic protocols. As in the applied pi-calculus, our protocol specification language is parametrized by a first-order sorted term signature and an equational theory which allows formalization of algebraic properties of cryptographic primitives. Our procedure is able to verify trace equivalence for determi-nate cryptographic protocols. On determinate protocols, trace equivalence coincides with observational equivalence which can therefore be automatically verified for such processes. When protocols are not determinate our procedure can be used for both under-and over-approximations of trace equivalence, which proved successful on examples. The procedure can handle a large set of cryptographic primitives, namely those that can be modeled by an optimally reducing convergent rewrite system. The procedure is based on a fully abstract modelling of the traces of a bounded number of sessions of the protocols into first-order Horn clauses on which a dedicated resolution procedure is used to decide equivalence properties. We have shown that our procedure terminates for the class of subterm convergent equational theories. Moreover, the procedure has been implemented in a prototype tool A-KiSs (Active Knowledge in Security Protocols) and has been effectively tested on examples. Some of the examples were outside the scope of existing tools, including checking anonymity of an electronic voting protocol

Formal Analysis of V2X Revocation Protocols

Research on vehicular networking (V2X) security has produced a range of security mechanisms and protocols tailored for this domain, addressing both security and privacy. Typically, the security analysis of these proposals has largely been informal. However, formal analysis can be used to expose flaws and ultimately provide a higher level of assurance in the protocols. This paper focusses on the formal analysis of a particular element of security mechanisms for V2X found in many proposals: the revocation of malicious or misbehaving vehicles from the V2X system by invalidating their credentials. This revocation needs to be performed in an unlinkable way for vehicle privacy even in the context of vehicles regularly changing their pseudonyms. The REWIRE scheme by Forster et al. and its subschemes BASIC and RTOKEN aim to solve this challenge by means of cryptographic solutions and trusted hardware. Formal analysis using the TAMARIN prover identifies two flaws with some of the functional correctness and authentication properties in these schemes. We then propose Obscure Token (OTOKEN), an extension of REWIRE to enable revocation in a privacy preserving manner. Our approach addresses the functional and authentication properties by introducing an additional key-pair, which offers a stronger and verifiable guarantee of successful revocation of vehicles without resolving the long-term identity. Moreover OTOKEN is the first V2X revocation protocol to be co-designed with a formal model.Comment: 16 pages, 4 figure

Verification of Cryptosystems Sustainability as the Main Criterion for Development of Common Information Security Policy

Security of data resources has become one of the main issues of modern society. Encryption is one of the most reliable ways to protect data from unauthorized disclosure. One of the key factors that influenced the formation of a new approach to information security is a significant growth of distributed-processing systems and use of computer networks for communication between users. It is a key reason to develop an information security policy

A Reduced Semantics for Deciding Trace Equivalence

Many privacy-type properties of security protocols can be modelled using trace equivalence properties in suitable process algebras. It has been shown that such properties can be decided for interesting classes of finite processes (i.e., without replication) by means of symbolic execution and constraint solving. However, this does not suffice to obtain practical tools. Current prototypes suffer from a classical combinatorial explosion problem caused by the exploration of many interleavings in the behaviour of processes. M\"odersheim et al. have tackled this problem for reachability properties using partial order reduction techniques. We revisit their work, generalize it and adapt it for equivalence checking. We obtain an optimisation in the form of a reduced symbolic semantics that eliminates redundant interleavings on the fly. The obtained partial order reduction technique has been integrated in a tool called APTE. We conducted complete benchmarks showing dramatic improvements.Comment: Accepted for publication in LMC

CRYPTOGRAPHIC PROTOCOL SECURITY IN NATIONAL ENCRYPTION APPLICATIONS

In the era of digital transformation, information exchange, especially confidential and strategic information has become the most vital aspect for almost all organizations. Various bad precedents regarding classified and strategic information leaks in Indonesia have become a slap in the face that must be acknowledge and answered with effective solutions. In 2020, XYZ Agency developed a file encryption application (ABC Application) to address the challenge of securing confidential information, especially those transmitted on electronic channels. Until 2022, the ABC Application has been implemented in a limited scope and its implementation is planned to be expanded nationally. After 2 years of operation, the XYZ Agency has conducted a study on the security of the algorithm used in ABC Application, but unfortunately has not conducted an in-depth study regarding the security of the protocol suite used in the Application. In this research, a security analysis of ABC application protocol suites, namely the registration protocol, user verification, key generation, and key request for the encryption-decryption process protocol was conducted through formal verification approach using the Scyther Tool. The analysis focuses on aspects of guaranteeing confidentiality of information and authentication with four criteria, namely secrecy, aliveness, synchronization, and agreement. The experimental results showed that these protocols meet the security criteria for the transmitted confidential information but have general weaknesses in the authentication aspect, especially for synchronization and agreement criteria. Based on these weaknesses, technical recommendations are proposed that are able to overcome the identified weaknesses

A reduced semantics for deciding trace equivalence using constraint systems

Many privacy-type properties of security protocols can be modelled using trace equivalence properties in suitable process algebras. It has been shown that such properties can be decided for interesting classes of finite processes (i.e., without replication) by means of symbolic execution and constraint solving. However, this does not suffice to obtain practical tools. Current prototypes suffer from a classical combinatorial explosion problem caused by the exploration of many interleavings in the behaviour of processes. M\"odersheim et al. have tackled this problem for reachability properties using partial order reduction techniques. We revisit their work, generalize it and adapt it for equivalence checking. We obtain an optimization in the form of a reduced symbolic semantics that eliminates redundant interleavings on the fly.Comment: Accepted for publication at POST'1