Abstract This paper studies several building blocks needed for electronic voting in order to prepare for the post-quantum era. In particular, we present lattice-based constructions for a generic zero-knowledge (ZK) proof of ballot correctness, a ZK proof of ballot correctness applicable for the homomorphic tallying scenario, and a ZK proof to achieve cast-as-intended verification during the vote casting period. We implement and benchmark our ballot correctness proofs, giving concrete estimations comparing the performance of homomorphic tallying and mix-net based e-voting systems in case of our lattice-based constructions.

This article describes an open-source quantum-resistant network traffic encryptor for the Linux platform. Our encryptor uses a combination of quantum and post-quantum key establishment methods to achieve quantum resistance combined with a fast encryption speed of AES to make quantum-resistant encryption readily available to the public. The packet-by-packet encryption architecture ensures that every bit of information is properly authenticated and encrypted. The combination of multiple key sources further increases the encryptor’s security – be it elliptic curve-based (Elliptic Curve Diffie Hellman, ECDH), quantum (Quantum Key Distribution, QKD) or post-quantum (CRYSTALS-Kyber). Without knowing all the keys obtained from different types of key sources, the final hybrid encryption key can only be obtained by brute-force means. Our contribution is very practical as the encryptor has reasonable performance, despite not being part of the Linux kernel.

This paper describes the efforts made for and lessons learnt from creating a decryption proof verifier for the Estonian IVXV Internet voting system. Our main conclusion is that cryptographic protocols aiming at providing transparency through verifiability should also take into account a non-functional requirement of low implementation complexity. We identify several steps of the verification protocol that could be made easier to implement without sacrificing security. A side-product of our effort is a fully functional IVXV decryption proof verifier written in Go that we used during the latest Estonian parliamentary elections of March 2023.

Abstract Mix‐networks were first proposed by Chaum in the late 1970s–early 1980s as a general tool for building anonymous communication systems. Classical mix‐net implementations rely on standard public key primitives (e.g., ElGamal encryption) that will become vulnerable when a sufficiently powerful quantum computer will be built. Thus, there is a need to develop quantum‐resistant mix‐nets. This article focuses on the application case of electronic voting where the number of votes to be mixed may reach hundreds of thousands or even millions. We propose an improved architecture for lattice‐based post‐quantum mix‐nets featuring more efficient zero‐knowledge proofs while maintaining established security assumptions. Our current implementation scales up to 100,000 votes, still leaving a lot of room for future optimisation.

In an ongoing discussion comparing the security properties of electronic and paper voting, decreased privacy is often presented as an argument against remote Internet voting. We contribute to this discussion by presenting a side-channel attack against the physical environment of traditional paper-based elections. More precisely, we build a device based on an Arduino development board and cheap electret microphones, capable of triangulating the locations of marks made on wooden tables with high precision. In the best configuration, we are able to determine the correct cell having dimensions 4×5 cm with more than 90% accuracy. This will allow breaching privacy of ballot sheet designs that rely on the voter marking her choice(s) between a potentially high number of candidates printed on one large sheet. We complement our attack with a study on various aspects of deployment of facial recognition. This gives rise to the setup where the attacker installs cameras in the polling stations, aiming at automated detection of people leaving the voting booths. Combining the two approaches, we will have a completely automated (and hence relatively well scalable) attack against the privacy of paper-based voting.

This paper extends the choice available for secure real number implementations with two new contributions. We will consider the numbers represented in form a-φ b where φ is the golden ratio, and in form (-1)s.2e where e is a fixed-point number. We develop basic arithmetic operations together with some frequently used elementary functions. All the operations are implemented and benchmarked on SHAREMIND secure multi-party computation framework. It turns out that the new proposals provide viable alternatives to standard floating- and fixed-point implementations from the performance/error viewpoint in various settings. However, the optimal choice still depends on the exact requirements of the numerical algorithm to be implemented.

In recent years, wireless sensor networks have been widely used in healthcare applications, such as hospital and home patient monitoring. Wireless medical sensor networks are more vulnerable to eavesdropping, modification, impersonation and replaying attacks than the wired networks. A lot of work has been done to secure wireless medical sensor networks. The existing solutions can protect the patient data during transmission, but cannot stop the inside attack where the administrator of the patient database reveals the sensitive patient data. In this paper, we propose a practical approach to prevent the inside attack by using multiple data servers to store patient data. The main contribution of this paper is securely distributing the patient data in multiple data servers and employing the Paillier and ElGamal cryptosystems to perform statistic analysis on the patient data without compromising the patients' privacy.

Recently, the amount of personal medical information online is increasing exponentially, opening up new avenues for hackers to expose personal data that, unlike financial information, can result in a permanent violation of privacy. To protect the privacy of patient data, such as electronic health records (EHRs), access control was used before and attributed-based encryption is used recently. These techniques can effectively prevent from the outside attacks, but are hard to withstand the inside attacks, where the database administrator or the key manager is an attacker. In this paper, we provide a solution to protect the privacy of patient data (EHRs) under the multi-party framework where all EHRs are encrypted with the common public key and an encrypted EHR can be decrypted only by the cooperation of all parties. Based on the ElGamal threshold public key encryption scheme, we propose several EHR access control protocols where multiple parties cooperate to control clinicians' access to EHRs without actually knowing EHRs. Our solution can protect the patient data against the inside attacks as long as at least one party can be trusted. Because our solution is built on Public Key Infrastructure (PKI), it facilitates the clinician registration and revocation.

In this paper we study the information security investment model proposed by Gordon and Loeb. We argue that the original model is missing at least one important restriction concerning monotonicity of the remaining vulnerability viewed as a function of original vulnerability level, and propose adding the respective condition. We present a new family of remaining vulnerability functions satisfying all the conditions and generalizing all the currently known example function families.

As more and more information becomes accessible via on-line databases, more public services can be provided and more complex queries involving several registers become feasible as well. However, not all of the digitally stored data is public and thus strict access control mechanisms must be enforced. At the same time, in order to take full advantage of on-line data sources, high availability must be achieved as well. This paper describes an infrastructure developed in Estonia to satisfy these somewhat contradictory requirements. This infrastructure (called X- Road) enables different organizations to access each other's data and rely on it when taking legally binding decisions. We discuss technical details ofX-Road together with the issues arising when the infrastructure is to be implemented on national or international level.

We propose an efficient and flexible system for a secure and authentic data exchange in a multiinstitutional environment, where the institutions maintain different databases and provide secure and limited access services to employees of other institutions. The main motivation for building such a system was to organize efficient cooperative use of state registers, in order to increase the efficiency and quality of public services in Estonia. In order to meet high security requirements, several contemporary measures are integrated (using digital signatures, distributing certificate information by means of DNS protocol and linking log files with cryptographic checksums). We give rationale for the design decisions made in the implementation process and conclude with the current state of public use of the resulting infrastructure.

Digital signature schemes are based on the assumption that the signing key is kept in secret. Ensuring that this assumption holds is one of the most crucial problems for all current digital signature applications. This paper describes the solution developed and prototyped by the authors - using a mobile computing device with a smart-card reader for creating digital signatures. We give an overview of several common settings for digital signature applications and the problems they have, also describing several frameworks for mobile security applications. A discussion about the choice of devices, design issues, concrete solutions and their security concerns follows. We conclude that although nothing can prevent careless private key handling, careful management is easier and more convenient when using our solution.