arXiv subjects

Thomas Haines

Publications and source records attributed to Thomas Haines.

5 recordsLinked to original sources

arXiv2022

Privacy Analysis of Samsung's Crowd-Sourced Bluetooth Location Tracking System

We present a detailed privacy analysis of Samsung's Offline Finding (OF) protocol, which is part of Samsung's Find My Mobile (FMM) location tracking system for locating Samsung mobile devices, such as Samsung smartphones and Bluetooth trackers (Galaxy SmartTags). The OF protocol uses Bluetooth Low Energy (BLE) to broadcast a unique beacon for a lost device. This beacon is then picked up by nearby Samsung phones or tablets (the {\em finder} devices), which then forward the unique beacon, along with the location it was detected at, to a Samsung managed server. The owner of a lost device can then query the server to locate their device. We examine several security and privacy related properties of the OF protocol and its implementation, from the perspectives of the owner, the finder and the vendor. These include examining: the possibility of identifying the owner of a device through the Bluetooth data obtained from the device, the possibility for a malicious actor to perform unwanted tracking against a person by exploiting the OF network, the possibility for the vendor to de-anonymise location reports to determine the locations of the owners or the finders of lost devices, and the possibility for an attacker to compromise the integrity of the location reports. Our findings suggest that there are privacy risks on all accounts, arising from issues in the design and the implementation of the OF protocol.

cs.CR↗

arXiv2022

Singularities of local models

We construct local models of Shimura varieties and investigate their singularities, with special emphasis on wildly ramified cases. More precisely, with the exception of odd unitary groups in residue characteristic $2$ we construct local models, show reducedness of their special fiber, Cohen$-$Macaulayness and in equi-characteristic also (pseudo-)rationality. In mixed characteristic we conjecture their (pseudo-)rationality. This is based on the construction of parahoric group schemes over two-dimensional bases for wildly ramified groups and an analysis of singularities of the attached Schubert varieties in positive characteristic using perfect geometry.

math.AG↗

arXiv2021

Towards Verifiable Remote Voting with Paper Assurance

We propose a protocol for verifiable remote voting with paper assurance. It is intended to augment existing postal voting procedures, allowing a ballot to be electronically constructed, printed on paper, then returned in the post. It allows each voter to verify that their vote has been correctly cast, recorded and tallied by the Electoral Commission. The system is not end-to-end verifiable, but does allow voters to detect manipulation by an adversary who controls either the voting device, or (the postal service and electoral commission) but not both. The protocol is not receipt-free, but if the client honestly follows the protocol (including possibly remembering everything), they cannot subsequently prove how they voted. Our proposal is the first to combine plain paper assurance with cryptographic verification in a (passively) receipt-free manner.

cs.CR↗

arXiv2019

A Description and Proof of a Generalised and Optimised Variant of Wikström's Mixnet

In this paper, we describe an optimised variant of Wikström's mixnet which shuffles vectors of ElGamal ciphertexts in parallel. We then show in detail that this construction is secure. Wikström's verifiable mixnet as we refer to it here was first presented in "Proofs of Restricted Shuffles" by Terelius and Wikström, building on Wikström's previous work. Specifically we take the optimised variant for ElGamal which appears to be in common use; for instance, it is presented in Haenni et al's "Pseudo-Code Algorithms for Verifiable Re-Encryption Mix-Nets". We extend the mixnet to support parallel shuffles. (The possibility of doing this is proven by the Wikström's result but we wish to show that this particular instance with its optimisations is secure.)

cs.CR↗

arXiv2009

The Satake isomorphism for special maximal parahoric Hecke algebras

Let G denote a connected reductive group over a nonarchimedean local field F. Let K denote a special maximal parahoric subgroup of G(F). We establish a Satake isomorphism for the Hecke algebra H of K-bi-invariant compactly supported functions on G(F). The key ingredient is a Cartan decomposition describing the double coset space K\G(F)/K. We also describe how our results relate to the treatment of Cartier, where K is replaced by a special maximal compact open subgroup K' of G(F) and where a Satake isomorphism is established for the Hecke algebra of K'-bi-invariant compactly supported functions on G(F).

math.RT↗