arXiv subjects

Ania M. Piotrowska

Publications and source records attributed to Ania M. Piotrowska.

4 recordsLinked to original sources

arXiv2025

Outfox: a Packet Format for a Layered Mixnet

Anonymous communication relies on encrypted packet formats that resist traffic analysis and ensure unlinkability. Sphinx, the current standard for mixnets, provides strong anonymity but relies on classical public-key cryptography, making it vulnerable to quantum attacks. In this paper, we present Outfox, a simplified variant of Sphinx tailored for mixnets with fixed-length routes and designed for post-quantum security. Outfox reduces both computational and communication costs. We formally define Outfox and prove its security in the Universal Composability (UC) framework. Our evaluation shows that Outfox retains strong anonymity guarantees while offering improved efficiency and adaptability to quantum-resistant cryptographic primitives.

cs.CR↗

arXiv2023

Compact and Divisible E-Cash with Threshold Issuance

Decentralized, offline, and privacy-preserving e-cash could fulfil the need for both scalable and byzantine fault-resistant payment systems. Existing offline anonymous e-cash schemes are unsuitable for distributed environments due to a central bank. We construct a distributed offline anonymous e-cash scheme, in which the role of the bank is performed by a quorum of authorities, and present its two instantiations. Our first scheme is compact, i.e. the cost of the issuance protocol and the size of a wallet are independent of the number of coins issued, but the cost of payment grows linearly with the number of coins spent. Our second scheme is divisible and thus the cost of payments is also independent of the number of coins spent, but the verification of deposits is more costly. We provide formal security proof of both schemes and compare the efficiency of their implementations.

cs.CR↗

arXiv2021

Studying the anonymity trilemma with a discrete-event mix network simulator

In this work, we present a discrete event mix network simulator, which allows analysing how anonymity, latency, and bandwidth overhead are affected by various scenarios of deployment and design choices. These design choices include network topology, mixing technique, volume of traffic, latency requirements, packet size or use of cover traffic. To the best of our knowledge, this is the first such simulator as work on it began in 2017 to analyze the Loopix mix network, and the code of our simulator is available under an open-source license. To demonstrate the capabilities of our simulator, we perform an empirical analysis of the impact of core design choices on anonymity, scalability and latency in Elixxir, HOPR and Nym, currently deployed mix network infrastructures that make a variety of different choices in their design.

cs.CR↗

arXiv2019

Extending the Anonymity of Zcash

Although Bitcoin in its original whitepaper stated that it offers anonymous transactions, de-anonymization techniques have found otherwise. Therefore, alternative cryptocurrencies, like Dash, Monero, and Zcash, were developed to provide better privacy. As Edward Snowden stated, "Zcash's privacy tech makes it the most interesting Bitcoin alternative (...) because the privacy properties of it are truly unique". Zcash's privacy is based on peer-reviewed cryptographic constructions, hence it is considered to provide the foundations for the best anonymity. However, even Zcash makes some privacy concessions. It does not protect users' privacy in the presence of a global adversary who is able to observe the whole network, and hence correlate the parties exchanging money, by using their network addresses. The recent empirical analysis of Zcash shows, that users often choose naive ways while performing the protocol operations, not realizing that it degrades their anonymity. In this talk, we will discuss an extension of Zcash using mix networks to enhance the privacy guarantees of users that choose to remain anonymous by tackling two major security challenges: one at the application layer of the scheme and one at its network layer.

cs.CR↗