Privacy compliance verification in cryptographic protocols

To provide privacy protection, cryptographic primitives are frequently applied to communication protocols in an open environment (e.g. the Internet). We call these protocols privacy enhancing protocols (PEPs) which constitute a class of cryptographic protocols. Proof of the security properties, in terms of the privacy compliance, of PEPs is desirable before they can be deployed. However, the traditional provable security approach, though well-established for proving the security of cryptographic primitives, is not applicable to PEPs. We apply the formal language of Coloured Petri Nets (CPNs) to construct an executable specification of a representative PEP, namely the Private Information Escrow Bound to Multiple Conditions Protocol (PIEMCP). Formal semantics of the CPN specification allow us to reason about various privacy properties of PIEMCP using state space analysis techniques. This investigation provides insights into the modelling and analysis of PEPs in general, and demonstrates the benefit of applying a CPN-based formal approach to the privacy compliance verification of PEPs

Modular Reasoning about Differential Privacy in a Probabilistic Process Calculus

International audienceThe verification of systems for protecting sensitive and confidential information is becoming an increasingly important issue. Differential privacy is a promising notion of privacy originated from the community of statistical databases, and now widely adopted in various models of computation. We consider a probabilistic process calculus as a specification formalism for concurrent systems, and we propose a framework for reasoning about the degree of differential privacy provided by such systems. In particular, we investigate the preservation of the degree of privacy under composition via the various operators. We illustrate our idea by proving an anonymity-preservation property for a variant of the Crowds protocol for which the standard analyses from the literature are inapplicable. Finally, we make some preliminary steps towards automatically computing the degree of privacy of a system in a compositional way

Modular Reasoning about Differential Privacy in a Probabilistic Process Calculus

International audienceThe verification of systems for protecting sensitive and confidential information is becoming an increasingly important issue. Differential privacy is a promising notion of privacy originated from the community of statistical databases, and now widely adopted in various models of computation. We consider a probabilistic process calculus as a specification formalism for concurrent systems, and we propose a framework for reasoning about the degree of differential privacy provided by such systems. In particular, we investigate the preservation of the degree of privacy under composition via the various operators. We illustrate our idea by proving an anonymity-preservation property for a variant of the Crowds protocol for which the standard analyses from the literature are inapplicable. Finally, we make some preliminary steps towards automatically computing the degree of privacy of a system in a compositional way

A Study on the Secure Online Examination System

13301甲第4475号博士（工学）金沢大学博士論文本文Full 以下に掲載：IJCANDI (International Journal of Computing and Informatics) 1(3) pp.90-100 2016. Universitas Mulawarman & Universiti Malaysia Sabah. 共著者：Abdul Wahid, Masahiro Mamb

Defining Privacy for Weighted Votes, Single and Multi-voter Coercion

Most existing formal privacy definitions for voting protocols are based on observational equivalence between two situations where two voters swap their votes. These definitions are unsuitable for cases where votes are weighted. In such a case swapping two votes can result in a different outcome and both situations become trivially distinguishable. We present a definition for privacy in voting protocols in the Applied Pi-Calculus that addresses this problem. Using our model, we are also able to define multi-voter coercion, i.e. situations where several voters are attacked at the same time. Then we prove that under certain realistic assumptions a protocol secure against coercion of a single voter is also secure against coercion of multiple voters. This applies for Receipt-Freeness as well as Coercion-Resistance

Inductive analysis of security protocols in Isabelle/HOL with applications to electronic voting

Security protocols are predefined sequences of message exchanges. Their uses over computer networks aim to provide certain guarantees to protocol participants. The sensitive nature of many applications resting on protocols encourages the use of formal methods to provide rigorous correctness proofs. This dissertation presents extensions to the Inductive Method for protocol verification in the Isabelle/HOL interactive theorem prover. The current state of the Inductive Method and of other protocol analysis techniques are reviewed. Protocol composition modelling in the Inductive Method is introduced and put in practice by holistically verifying the composition of a certification protocol with an authentication protocol. Unlike some existing approaches, we are not constrained by independence requirements or search space limitations. A special kind of identity-based signatures, auditable ones, are specified in the Inductive Method and integrated in an analysis of a recent ISO/IEC 9798-3 protocol. A side-by-side verification features both a version of the protocol with auditable identity-based signatures and a version with plain ones. The largest part of the thesis presents extensions for the verification of electronic voting protocols. Innovative specification and verification strategies are described. The crucial property of voter privacy, being the impossibility of knowing how a specific voter voted, is modelled as an unlinkability property between pieces of information. Unlinkability is then specified in the Inductive Method using novel message operators. An electronic voting protocol by Fujioka, Okamoto and Ohta is modelled in the Inductive Method. Its classic confidentiality properties are verified, followed by voter privacy. The approach is shown to be generic enough to be re-usable on other protocols while maintaining a coherent line of reasoning. We compare our work with the widespread process equivalence model and examine respective strengths

Guess my vote : a study of opacity and information flow in voting systems

With an overall theme of information flow, this thesis has two main strands. In the first part of the thesis, I review existing information flow properties, highlighting a recent definition known as opacity [25]. Intuitively, a predicate cP is opaque if for every run in which cP is true, there exists an indistinguishable run in which it is false, where a run can be regarded as a sequence of events. Hence, the observer is never able to establish the truth of cPo The predicate cP can be defined according to requirements of the system, giving opacity a great deal of flexibility and versatility. Opacity is then studied in relation to several well-known definitions for information flow. As will be shown, several of these properties can be cast as variations of opacity, while others have a relationship by implication with the opacity property [139]. This demonstrates the flexibility of opacity, at the same time establishing its distinct character. In the second part of the thesis, I investigate information flow in voting systems. Pret a Voter [36] is the main exemplar, and is compared to other schemes in the case study. I first analyse information flow in Pret a Voter and the FOO scheme [59], concentrating on the core protocols. The aim is to investigate the security requirements of each scheme, and the extent to which they can be captured using opacity. I then discuss a systems-based analysis of Pret a Voter [163], which adapts and extends an earlier analysis of the Chaum [35] and Neff [131]' [132]' [133] schemes in [92]. Although this analysis has identified several potential vulnerabilities, it cannot be regarded as systematic, and a more rigorous approach may be necessary. It is possible that a combination of the information flow and systems- based analyses might be the answer. The analysis of coercion-resistance, which is performed on Pret a Voter and the FOO scheme, may exemplify this more systematic approach. Receipt-freeness usually means that the voter is unable to construct a proof of her vote. Coercion-resistance is a stronger property in that it accounts for the possibility of interaction between the coercer and the voter during protocol execution. It appears that the opacity property is ideally suited to expressing the requirements for coercion-resistance in each scheme. A formal definition of receipt-freeness cast as a variation of opacity is proposed [138], together with suggestions on how it might be reinforced to capture coercion-resistance. In total, the thesis demonstrates the remarkable flexibility of opacity, both in expressing differing security requirements and as a tool for security analysis. This work lays the groundwork for future enhancement of the opacity framework.EThOS - Electronic Theses Online ServiceDSTL : EPSRCGBUnited Kingdo

Cryptography in privacy-preserving applications.

Tsang Pak Kong.Thesis (M.Phil.)--Chinese University of Hong Kong, 2005.Includes bibliographical references (leaves 95-107).Abstracts in English and Chinese.Abstract --- p.iiAcknowledgement --- p.ivChapter 1 --- Introduction --- p.1Chapter 1.1 --- Privacy --- p.1Chapter 1.2 --- Cryptography --- p.5Chapter 1.2.1 --- History of Cryptography --- p.5Chapter 1.2.2 --- Cryptography Today --- p.6Chapter 1.2.3 --- Cryptography For Privacy --- p.7Chapter 1.3 --- Thesis Organization --- p.8Chapter 2 --- Background --- p.10Chapter 2.1 --- Notations --- p.10Chapter 2.2 --- Complexity Theory --- p.11Chapter 2.2.1 --- Order Notation --- p.11Chapter 2.2.2 --- Algorithms and Protocols --- p.11Chapter 2.2.3 --- Relations and Languages --- p.13Chapter 2.3 --- Algebra and Number Theory --- p.14Chapter 2.3.1 --- Groups --- p.14Chapter 2.3.2 --- Intractable Problems --- p.16Chapter 2.4 --- Cryptographic Primitives --- p.18Chapter 2.4.1 --- Public-Key Encryption --- p.18Chapter 2.4.2 --- Identification Protocols --- p.21Chapter 2.4.3 --- Digital Signatures --- p.22Chapter 2.4.4 --- Hash Functions --- p.24Chapter 2.4.5 --- Zero-Knowledge Proof of Knowledge --- p.26Chapter 2.4.6 --- Accumulators --- p.32Chapter 2.4.7 --- Public Key Infrastructure --- p.34Chapter 2.5 --- Zero Knowledge Proof of Knowledge Protocols in Groups of Unknown Order --- p.36Chapter 2.5.1 --- The Algebraic Setting --- p.36Chapter 2.5.2 --- Proving the Knowledge of Several Discrete Logarithms . --- p.37Chapter 2.5.3 --- Proving the Knowledge of a Representation --- p.38Chapter 2.5.4 --- Proving the Knowledge of d Out of n Equalities of Discrete Logarithms --- p.39Chapter 2.6 --- Conclusion --- p.42Chapter 3 --- Related Works --- p.43Chapter 3.1 --- Introduction --- p.43Chapter 3.2 --- Group-Oriented Signatures without Spontaneity and/or Anonymity --- p.44Chapter 3.3 --- SAG Signatures --- p.46Chapter 3.4 --- Conclusion --- p.49Chapter 4 --- Linkable Ring Signatures --- p.50Chapter 4.1 --- Introduction --- p.50Chapter 4.2 --- New Notions --- p.52Chapter 4.2.1 --- Accusatory Linking --- p.52Chapter 4.2.2 --- Non-slanderability --- p.53Chapter 4.2.3 --- Linkability in Threshold Ring Signatures --- p.54Chapter 4.2.4 --- Event-Oriented Linking --- p.55Chapter 4.3 --- Security Model --- p.56Chapter 4.3.1 --- Syntax --- p.56Chapter 4.3.2 --- Notions of Security --- p.58Chapter 4.4 --- Conclusion --- p.63Chapter 5 --- Short Linkable Ring Signatures --- p.64Chapter 5.1 --- Introduction --- p.64Chapter 5.2 --- The Construction --- p.65Chapter 5.3 --- Security Analysis --- p.68Chapter 5.3.1 --- Security Theorems --- p.68Chapter 5.3.2 --- Proofs --- p.68Chapter 5.4 --- Discussion --- p.70Chapter 5.5 --- Conclusion --- p.71Chapter 6 --- Separable Linkable Threshold Ring Signatures --- p.72Chapter 6.1 --- Introduction --- p.72Chapter 6.2 --- The Construction --- p.74Chapter 6.3 --- Security Analysis --- p.76Chapter 6.3.1 --- Security Theorems --- p.76Chapter 6.3.2 --- Proofs --- p.77Chapter 6.4 --- Discussion --- p.79Chapter 6.5 --- Conclusion --- p.80Chapter 7 --- Applications --- p.82Chapter 7.1 --- Offline Anonymous Electronic Cash --- p.83Chapter 7.1.1 --- Introduction --- p.83Chapter 7.1.2 --- Construction --- p.84Chapter 7.2 --- Electronic Voting --- p.85Chapter 7.2.1 --- Introduction --- p.85Chapter 7.2.2 --- Construction . --- p.87Chapter 7.2.3 --- Discussions --- p.88Chapter 7.3 --- Anonymous Attestation --- p.89Chapter 7.3.1 --- Introduction --- p.89Chapter 7.3.2 --- Construction --- p.90Chapter 7.4 --- Conclusion --- p.91Chapter 8 --- Conclusion --- p.92A Paper Derivation --- p.94Bibliography --- p.9