More security or less insecurity

We depart from the conventional quest for ‘Completely Secure Systems’ and ask ‘How can we be more Secure’. We draw heavily from the evolution of the Theory of Justice and the arguments against the institutional approach to Justice. Central to our argument is the identification of redressable insecurity, or weak links. Our contention is that secure systems engineering is not really about building perfectly secure systems but about redressing manifest insecurities.Final Accepted Versio

Towards quantum-based privacy and voting

The privacy of communicating participants is often of paramount importance, but in some situations it is an essential condition. A typical example is a fair (secret) voting. We analyze in detail communication privacy based on quantum resources, and we propose new quantum protocols. Possible generalizations that would lead to voting schemes are discussed.Comment: 5 pages, improved description of the protoco

Anonymous quantum communication

We present the first protocol for the anonymous transmission of a quantum state that is information-theoretically secure against an active adversary, without any assumption on the number of corrupt participants. The anonymity of the sender and receiver is perfectly preserved, and the privacy of the quantum state is protected except with exponentially small probability. Even though a single corrupt participant can cause the protocol to abort, the quantum state can only be destroyed with exponentially small probability: if the protocol succeeds, the state is transferred to the receiver and otherwise it remains in the hands of the sender (provided the receiver is honest).Comment: 11 pages, to appear in Proceedings of ASIACRYPT, 200

Zero-knowledge undeniable signatures (extended abstract)

Undeniable signature protocols were introduced at Crypto '89 [CA]. The present article contains new undeniable signature protocols, and these are the first that are zero-knowledge

Quantum protocols for anonymous voting and surveying

We describe quantum protocols for voting and surveying. A key feature of our schemes is the use of entangled states to ensure that the votes are anonymous and to allow the votes to be tallied. The entanglement is distributed over separated sites; the physical inaccessibility of any one site is sufficient to guarantee the anonymity of the votes. The security of these protocols with respect to various kinds of attack is discussed. We also discuss classical schemes and show that our quantum voting protocol represents a N-fold reduction in computational complexity, where N is the number of voters.Comment: 8 pages. V2 includes the modifications made for the published versio

The anonymous subgraph problem

In this work we address the Anonymous Subgraph Problem (ASP). The problem asks to decide whether a directed graph contains anonymous subgraphs of a given family. This problem has a number of practical applications and here we describe three of them (Secret Santa Problem, anonymous routing, robust paths) that can be formulated as ASPs. Our main contributions are (i) a formalization of the anonymity property for a generic family of subgraphs, (ii) an algorithm to solve the ASP in time polynomial in the size of the graph under a set of conditions, and (iii) a thorough evaluation of our algorithms using various tests based both on randomly generated graphs and on real-world instances

How to Issue a Central Bank Digital Currency

With the emergence of Bitcoin and recently proposed stablecoins from BigTechs, such as Diem (formerly Libra), central banks face growing competition from private actors offering their own digital alternative to physical cash. We do not address the normative question whether a central bank should issue a central bank digital currency (CBDC) or not. Instead, we contribute to the current research debate by showing how a central bank could do so, if desired. We propose a token-based system without distributed ledger technology and show how earlier-deployed, software-only electronic cash can be improved upon to preserve transaction privacy, meet regulatory requirements in a compelling way, and offer a level of quantum-resistant protection against systemic privacy risk. Neither monetary policy nor financial stability would be materially affected because a CBDC with this design would replicate physical cash rather than bank deposits.Comment: Swiss National Bank Working Paper3/202