David Mödinger hat 2015 seinen Masterabschluss an der Universität Ulm erhalten und arbeitet seit August 2015 im Institut für Verteilte Systeme.
Derzeit arbeite ich am Projekt PriCloud, einem Projekt der Landesstiftung Baden-Württemberg zur Erforschung Privatsphäre schützender Cloud-Speicher.
A Flexible Network Approach to Privacy of Blockchain Transactions
Proceedings of the 38th International Conference on Distributed Computing Systems
Zusammenfassung: For preserving privacy, blockchains can be equipped with dedicated mechanisms to anonymize participants. How- ever, these mechanism often take only the abstraction layer of blockchains into account whereas observations of the underlying network traffic can reveal the originator of a transaction request. Previous solutions either provide topological privacy that can be broken by attackers controlling a large number of nodes, or offer strong and cryptographic privacy but are inefficient up to practical unusability. Further, there is no flexible way to trade privacy against efficiency to adjust to practical needs. We propose a novel approach that combines existing mechanisms to have quantifiable and adjustable cryptographic privacy which is further improved by augmented statistical measures that prevent frequent attacks with lower resources. This approach achieves flexibility for privacy and efficency requirements of different blockchain use cases.
Towards Enhanced Network Privacy for Blockchains
Short research statement for the DSN Workshop on Byzantine Consensus and Resilient Blockchains 2018
Zusammenfassung: Privacy aspects of blockchains have gained attention as the log of transactions can be view by any interested party. Privacy mechanisms applied to the ledger can be undermined by attackers on the network level, resulting in deanonymization of the transaction senders. We discuss current approaches to this problem, e.g. Dandelion, sketch our own approach to provide even stronger privacy mechanisms and discuss the challenges and open questions for further research in this area.
Blackchain: Scalability for Resource-Constrained Accountable Vehicle-to-X Communication
SERIAL'17: SERIAL'17: ScalablE and Resilient InfrAstructures for distributed Ledgers, December 11--15, 2017, Las Vegas, NV, USA
PriCloud: A Distributed File Storage with Financial Incentives
Poster at 1st ForDigital Blockchain Workshop
Design of a Privacy-Preserving Decentralized File Storage with Financial Incentives
Proc. of IEEE Security & Privacy on the Blockchain (IEEE S&B) (affiliated with EUROCRYPT 2017)
Zusammenfassung: Surveys indicate that users are often afraid to entrust data to cloud storage providers, because these do not offer sufficient privacy. On the other hand, peer-2-peer–based privacy-preserving storage systems like Freenet suffer from a lack of contribution and storage capacity, since there is basically no incentive to contribute own storage capacity to other participants in the network. We address these contradicting requirements by a design which combines a distributed storage with a privacy-preserving blockchain-based payment system to create incentives for participation while maintaining user privacy. By following a Privacy-by-Design strategy integrating privacy throughout the whole system life cycle, we show that it is possible to achieve levels of privacy comparable to state-of-the-art distributed storage technologies, despite integrating a payment mechanism. Our results show that it is possible to combine storage contracts and payments in a privacy-preserving way. Further, our system design may serve as an inspiration for future similar architectures.
Using Conflict-Free Replicated Data Types for Serverless Mobile Social Applications
Proceedings of the 8th ACM International Workshop on Hot Topics in Planet-scale mObile computing and online Social neTworking , Seite 49-54.
Zusammenfassung: A basic reason for backend systems in mobile application architectures is the centralized management of state. Mobile clients synchronize local states with the backend in order to maintain an up-to-date view of the application state. As not all mobile social applications require strong consistency guarantees, we survey an alternative approach using special data structures for mobile applications. These data structures only provide eventual consistency, but allow for conflict-free replication between peers. Our analysis collects the requirements of social mobile applications for being suitable for this approach. Based on exemplary mobile social applications, we also point out the benefits of serverless architecture or architectures with a thin backend layer.
Decoding Interleaved Gabidulin Codes using Alekhnovich's Algorithm
Algebraic and Combinatorial Coding Theory 2016
Zusammenfassung: We prove that Alekhnovich’s algorithm can be used for row reduction of skew polynomial matrices. This yields an O(`3 n(ω+1)/2 log(n)) decoding algorithm for Interleaved Gabidulin codes of length n, where ω is the matrix multiplication exponent, improving in the exponent of n compared to previous results.
An Alternative Decoding Method for Gabidulin Codes in Characteristic Zero
International Symposium on Information Theory (ISIT), 2016 IEEE
Herausgeber: IEEE, Barcelona, Spain
Zusammenfassung: Gabidulin codes, originally defined over finite fields, are an important class of rank metric codes with various applications. Recently, their definition was generalized to certain fields of characteristic zero and a Welch--Berlekamp like algorithm with complexity O(n^3) was given. We propose a new application of Gabidulin codes over infinite fields: low-rank matrix recovery. Also, an alternative decoding approach is presented based on a Gao type key equation, reducing the complexity to at least O(n^2). This method immediately connects the decoding problem to well-studied problems, which have been investigated in terms of coefficient growth and numerical stability.