Christoph Egger
Christoph Egger IRIF, Université Paris Cité Bâtiment Sophie Germain, Office 4058 8 Place Aurélie Nemours, 75205 Paris Email: Christoph.Egger@irif.fr Jabber: christoph@egger.im PGP
9FED 5C6C E206 B70A 5857 70CA 9655 22B9 D49A E731 3C1F 32FB E637 85F2 4461 4AD2 53C2 B1F9 83C5 BAA3
About Me
I am a researcher at Institut de Recherche en Informatique Fondamentale (IRIF) since fall 2022 with a focus on the connection between cryptography and space-time tradeofs as well as fine-grained complexity. During my doctoral studies I worked on formalization and proof techniques to manage large real-world systems and establishing solid foundations to asses non-cryptographic aspects of anonymity among other topics. As a master student I worked on Modal Logic and Category Theory and as a Bachelor Student on Anonymous Communication and Software Product Lines. I am also a founding member of the FAUST CTF team and its own competition, FAUST-CTF. Finally I am a Free Software person. I have been a Debian Developer for more than 10 years and have contributed to a variety of software projects including the Linux kernel and the Git version control system.
Research Interests
Currently I am working on connections between complexity theory and cryptography. In particular I am interested in computational security outside the relativizing setting as well as work to better understand minicrypt security.
My most recent results concern cryptographic proofs: Composability (both in the classical Universal Composability interpretation as well as composition and modularization of proofs) and extending security from cryptographic primitives towards their concrete use (for example concerning Ring Signatures and Steganography).
In the past I have worked, among other things, on System Software Engineering and Software Product Lines, Coalgebraic Modal Logic and Anonymity Networks.
Free Software
I am a Debian Developer since December 2009, my first contributions go back to 2016. From roughly 2010 to 2016 I have been a core member of the kFreeBSD team supporting this rather unusual combination of BSD and GNU components. Additionally, many small contributions to different Free Software projects are the result of my Debian work. I have initiated the internationalization effort of Unknown Horizons originally implementing its multi-language support. As a research assistant in the VAMOS research project I contributed more than 50 changes to the Linux Kernel. I also added public key pinning support to the Git version control system.
Internships & Research Visits
- Aug. 2020 - Nov. 2020: Aalto University working with Christopher Brzuska on State Separation Proofs and Key-Exchange
- Sept. 2018 - Dec. 2018: TU Wien Security and Privacy Group, working with Matteo Maffei and Pedro Moreno-Sanchez on payment channel networks
- Sept. 2012 - Feb. 2013: UCSB seclab, working with Christopher Kruegel and Giovanni Vigna on the systematic analysis of the I2P anonymity system
Grants & Fellowships
- Math in Greater Paris: Two-Year postdoctoral fellowship cofunded by EU H2020 Marie Sklodowska-Curie Action and FSMP
Comunity Service
Program committees & editorial boards
Other reviewing activities
- 2020, 2021, 2022: External Reviewer for Proceedings on Privacy Enhancing Technologies
- 2019, 2020, 2021: Reviewer for IACR Crypto
- 2018: External Reviewer for IEEE Transactions on Information Forensics & Security
- 2021: External Reviewer for ACM Transactions on Privacy and Security
- Subreviewer on multiple occasions including TCC'21, CCS'19, S&P'21 and SCN'22
Teaching
In summer 2021 Viktoria Ronge and I designed and taught a one-week summer school course for high-school students. Focus of the course was on cryptographic methodology and zero-knowledge proof systems. Also with Viktoria Ronge in Fall 2019 I organized a (graduate level) seminar on privacy notions.
In addition I have been (co-)responsible for the exercise sessions in multiple courses including "Secure Multi-Party Computation", "Password Based Cryptography" and blockchain-related lectures.
Publications
@article{DBLP:journals/iacr/BrzuskaDEFKK21,
author = {Chris Brzuska and
Antoine Delignat{-}Lavaud and
Christoph Egger and
C{\'{e}}dric Fournet and
Konrad Kohbrok and
Markulf Kohlweiss},
title = {Key-schedule Security for the {TLS} 1.3 Standard},
journal = {{IACR} Cryptol. ePrint Arch.},
pages = {467},
year = {2021},
url = {https://eprint.iacr.org/2021/467},
timestamp = {Fri, 23 Apr 2021 12:06:25 +0200},
biburl = {https://dblp.org/rec/journals/iacr/BrzuskaDEFKK21.bib},
bibsource = {dblp computer science bibliography, https://dblp.org}
}
In a ring-signature-based anonymous cryptocurrency, signers of a transaction are hidden among a set of potential signers, called a ring, whose size is much smaller than the number of all users. The ringmembership relations specified by the sets of transactions thus induce bipartite transaction graphs, whose distribution is in turn induced by the ring sampler underlying the cryptocurrency. Since efficient graph analysis could be performed on transaction graphs to potentially deanonymise signers, it is crucial to understand the resistance of (the transaction graphs induced by) a ring sampler against graph analysis. Of particular interest is the class of partitioning ring samplers. Although previous works showed that they provide almost optimal local anonymity, their resistance against global, e.g. graph-based, attacks were unclear. In this work, we analyse transaction graphs induced by partitioning ring samplers. Specifically, we show (partly analytically and partly empirically) that, somewhat surprisingly, by setting the ring size to be at least logarithmic in the number of users, a graph-analysing adversary is no better than the one that performs random guessing in deanonymisation up to constant factor of 2.
@article{DBLP:journals/popets/EggerLRWY22,
author = {Christoph Egger and
Russell W. F. Lai and
Viktoria Ronge and
Ivy K. Y. Woo and
Hoover H. F. Yin},
title = {On Defeating Graph Analysis of Anonymous Transactions},
journal = {Proc. Priv. Enhancing Technol.},
volume = {2022},
number = {3},
pages = {538--557},
year = {2022},
url = {https://doi.org/10.56553/popets-2022-0085},
doi = {10.56553/popets-2022-0085},
timestamp = {Wed, 27 Jul 2022 22:16:25 +0200},
biburl = {https://dblp.org/rec/journals/popets/EggerLRWY22.bib},
bibsource = {dblp computer science bibliography, https://dblp.org}
}
@inproceedings{DBLP:conf/ccs/00010R0KS21,
author = {Mike Graf and
Daniel Rausch and
Viktoria Ronge and
Christoph Egger and
Ralf K{\"{u}}sters and
Dominique Schr{\"{o}}der},
editor = {Yongdae Kim and
Jong Kim and
Giovanni Vigna and
Elaine Shi},
title = {A Security Framework for Distributed Ledgers},
booktitle = {{CCS} '21: 2021 {ACM} {SIGSAC} Conference on Computer and Communications
Security, Virtual Event, Republic of Korea, November 15 - 19, 2021},
pages = {1043--1064},
publisher = {{ACM}},
year = {2021},
url = {https://doi.org/10.1145/3460120.3485362},
doi = {10.1145/3460120.3485362},
timestamp = {Mon, 03 Jan 2022 22:18:49 +0100},
biburl = {https://dblp.org/rec/conf/ccs/00010R0KS21.bib},
bibsource = {dblp computer science bibliography, https://dblp.org}
}
A ring signature scheme allows the signer to sign on behalf of an ad hoc set of users, called a ring. The verifier can be convinced that a ring member signs, but cannot point to the exact signer. Ring signatures have become increasingly important today with their deployment in anonymous cryptocurrencies. Conventionally, it is implicitly assumed that all ring members are equally likely to be the signer. This assumption is generally false in reality, leading to various practical and devastating deanonymizing attacks in Monero, one of the largest anonymous cryptocurrencies. These attacks highlight the unsatisfactory situation that how a ring should be chosen is poorly understood.
We propose an analytical model of ring samplers towards a deeper understanding of them through systematic studies. Our model helps to describe how anonymous a ring sampler is with respect to a given signer distribution as an information-theoretic measure. We show that this measure is robust – it only varies slightly when the signer distribution varies slightly. We then analyze three natural samplers – uniform, mimicking, and partitioning – under our model with respect to a family of signer distributions modeled after empirical Bitcoin data. We hope that our work paves the way towards researching ring samplers from a theoretical point of view.
@article{DBLP:journals/popets/RongeELSY21,
author = {Viktoria Ronge and
Christoph Egger and
Russell W. F. Lai and
Dominique Schr{\"{o}}der and
Hoover H. F. Yin},
title = {Foundations of Ring Sampling},
journal = {Proc. Priv. Enhancing Technol.},
volume = {2021},
number = {3},
pages = {265--288},
year = {2021},
url = {https://doi.org/10.2478/popets-2021-0047},
doi = {10.2478/popets-2021-0047},
timestamp = {Thu, 14 Oct 2021 09:26:27 +0200},
biburl = {https://dblp.org/rec/journals/popets/RongeELSY21.bib},
bibsource = {dblp computer science bibliography, https://dblp.org}
}
Background
The development of Precision Medicine strategies requires high-dimensional phenotypic and genomic data, both of which are highly privacy-sensitive data types. Conventional data management systems lack the capabilities to sufficiently handle the expected large quantities of such sensitive data in a secure manner. PROMISE is a genetic data management concept that implements a highly secure platform for data exchange while preserving patient interests, privacy, and autonomy.
Methods
The concept of PROMISE to democratize genetic data was developed by an interdisciplinary team. It integrates a sophisticated cryptographic concept that allows only the patient to grant selective access to defined parts of his genetic information with single DNA base-pair resolution cryptography. The PROMISE system was developed for research purposes to evaluate the concept in a pilot study with nineteen cardiomyopathy patients undergoing genotyping, questionnaires, and longitudinal follow-up.
Results
The safety of genetic data was very important to 79%, and patients generally regarded the data as highly sensitive. More than half the patients reported that their attitude towards the handling of genetic data has changed after using the PROMISE app for 4 months (median). The patients reported higher confidence in data security and willingness to share their data with commercial third parties, including pharmaceutical companies (increase from 5 to 32%).
Conclusion
PROMISE democratizes genomic data by a transparent, secure, and patient-centric approach. This clinical pilot study evaluating a genetic data infrastructure is unique and shows that patient’s acceptance of data sharing can be increased by patient-centric decision-making.
Graphic abstract
@Article{Amr2022,
author="Amr, Ali
and Hinderer, Marc
and Griebel, Lena
and Deuber, Dominic
and Egger, Christoph
and Sedaghat-Hamedani, Farbod
and Kayvanpour, Elham
and Huhn, Daniel
and Haas, Jan
and Frese, Karen
and Schweig, Marc
and Marnau, Ninja
and Kr{\"a}mer, Annika
and Durand, Claudia
and Battke, Florian
and Prokosch, Hans-Ulrich
and Backes, Michael
and Keller, Andreas
and Schr{\"o}der, Dominique
and Katus, Hugo A.
and Frey, Norbert
and Meder, Benjamin",
title="Controlling my genome with my smartphone: first clinical experiences of the PROMISE system",
journal="Clinical Research in Cardiology",
year="2022",
month="Jun",
day="01",
volume="111",
number="6",
pages="638--650",
abstract="The development of Precision Medicine strategies requires high-dimensional phenotypic and genomic data, both of which are highly privacy-sensitive data types. Conventional data management systems lack the capabilities to sufficiently handle the expected large quantities of such sensitive data in a secure manner. PROMISE is a genetic data management concept that implements a highly secure platform for data exchange while preserving patient interests, privacy, and autonomy.",
issn="1861-0692",
doi="10.1007/s00392-021-01942-8",
url="https://doi.org/10.1007/s00392-021-01942-8"
}
@inproceedings{DBLP:conf/mie/GriebelHAMSD0KK20,
author = {Lena Griebel and
Marc Hinderer and
Ali Amr and
Benjamin Meder and
Marc Schweig and
Dominic Deuber and
Christoph Egger and
Claudia Kawohl and
Annika Kr{\"{a}}mer and
Isabell Flade and
Dominique Schr{\"{o}}der and
Hans{-}Ulrich Prokosch},
editor = {Louise Bilenberg Pape{-}Haugaard and
Christian Lovis and
Inge Cort Madsen and
Patrick Weber and
Per Hostrup Nielsen and
Philip Scott},
title = {The Patient as Genomic Data Manager - Evaluation of the {PROMISE}
App},
booktitle = {Digital Personalized Health and Medicine - Proceedings of {MIE} 2020,
Medical Informatics Europe, Geneva, Switzerland, April 28 - May 1,
2020},
series = {Studies in Health Technology and Informatics},
volume = {270},
pages = {1061--1065},
publisher = {{IOS} Press},
year = {2020},
url = {https://doi.org/10.3233/SHTI200324},
doi = {10.3233/SHTI200324},
timestamp = {Wed, 21 Jul 2021 17:50:05 +0200},
biburl = {https://dblp.org/rec/conf/mie/GriebelHAMSD0KK20.bib},
bibsource = {dblp computer science bibliography, https://dblp.org}
}
@inproceedings{DBLP:conf/ccs/Brost0LSSZ20,
author = {Julian Brost and
Christoph Egger and
Russell W. F. Lai and
Fritz Schmid and
Dominique Schr{\"{o}}der and
Markus Zoppelt},
editor = {Jay Ligatti and
Xinming Ou and
Jonathan Katz and
Giovanni Vigna},
title = {Threshold Password-Hardened Encryption Services},
booktitle = {{CCS} '20: 2020 {ACM} {SIGSAC} Conference on Computer and Communications
Security, Virtual Event, USA, November 9-13, 2020},
pages = {409--424},
publisher = {{ACM}},
year = {2020},
url = {https://doi.org/10.1145/3372297.3417266},
doi = {10.1145/3372297.3417266},
timestamp = {Fri, 09 Apr 2021 18:39:46 +0200},
biburl = {https://dblp.org/rec/conf/ccs/Brost0LSSZ20.bib},
bibsource = {dblp computer science bibliography, https://dblp.org}
}
@inproceedings{DBLP:conf/ccs/0001MM19,
author = {Christoph Egger and
Pedro Moreno{-}Sanchez and
Matteo Maffei},
editor = {Lorenzo Cavallaro and
Johannes Kinder and
XiaoFeng Wang and
Jonathan Katz},
title = {Atomic Multi-Channel Updates with Constant Collateral in Bitcoin-Compatible
Payment-Channel Networks},
booktitle = {Proceedings of the 2019 {ACM} {SIGSAC} Conference on Computer and
Communications Security, {CCS} 2019, London, UK, November 11-15, 2019},
pages = {801--815},
publisher = {{ACM}},
year = {2019},
url = {https://doi.org/10.1145/3319535.3345666},
doi = {10.1145/3319535.3345666},
timestamp = {Thu, 14 Oct 2021 09:58:24 +0200},
biburl = {https://dblp.org/rec/conf/ccs/0001MM19.bib},
bibsource = {dblp computer science bibliography, https://dblp.org}
}
An individual’s genetic information is possibly the most valuable personal information. While knowledge of a person’s DNA sequence can facilitate the diagnosis of several heritable diseases and allow personalized treatment, its exposure comes with significant threats to the patient’s privacy. Currently known solutions for privacy-respecting computation require the owner of the DNA to either be heavily involved in the execution of a cryptographic protocol or to completely outsource the access control to a third party. This motivates the demand for cryptographic protocols which enable computation over encrypted genomic data while keeping the owner of the genome in full control. We envision a scenario where data owners can exercise arbitrary and dynamic access policies, depending on the intended use of the analysis results and on the credentials of who is conducting the analysis. At the same time, data owners are not required to maintain a local copy of their entire genetic data and do not need to exhaust their computational resources in an expensive cryptographic protocol.
In this work, we present METIS, a system that assists the computation over encrypted data stored in the cloud while leaving the decision on admissible computations to the data owner. It is based on garbled circuits and supports any polynomially-computable function. A critical feature of our system is that the data owner is free from computational overload and her communication complexity is independent of the size of the input data and only linear in the size of the circuit’s output. We demonstrate the practicality of our approach with an implementation and an evaluation of several functions over real datasets.
@article{DBLP:journals/popets/DeuberEFMSTBD19,
author = {Dominic Deuber and
Christoph Egger and
Katharina Fech and
Giulio Malavolta and
Dominique Schr{\"{o}}der and
Sri Aravinda Krishnan Thyagarajan and
Florian Battke and
Claudia Durand},
title = {My Genome Belongs to Me: Controlling Third Party Computation on Genomic
Data},
journal = {Proc. Priv. Enhancing Technol.},
volume = {2019},
number = {1},
pages = {108--132},
year = {2019},
url = {https://doi.org/10.2478/popets-2019-0007},
doi = {10.2478/popets-2019-0007},
timestamp = {Tue, 01 Sep 2020 13:13:12 +0200},
biburl = {https://dblp.org/rec/journals/popets/DeuberEFMSTBD19.bib},
bibsource = {dblp computer science bibliography, https://dblp.org}
}
Passwords and access control remain the popular choice for protecting sensitive data stored online, despite their well-known vulnerability to brute-force attacks. A natural solution is to use encryption. Although standard practices of using encryption somewhat alleviate the problem, decryption is often needed for utility, and keeping the decryption key within reach is obviously dangerous. To address this seemingly unavoidable problem in data security, we propose password-hardened encryption (PHE). With the help of an external crypto server, a service provider can recover the user data encrypted by PHE only when an end user supplied a correct password. PHE inherits the security features of password-hardening (Usenix Security ’15), adding protection for the user data. In particular, the crypto server does not learn any information about any user data. More importantly, both the crypto server and the service provider can rotate their secret keys, a proactive security mechanism mandated by the Payment Card Industry Data Security Standard (PCI DSS). We build an extremely simple password-hardened encryption scheme. Compared with the state-of-the-art password-hardening scheme (Usenix Security ’17), our scheme only uses minimal number-theoretic operations and is, therefore, 30% - 50% more efficient. In fact, our extensive experimental evaluation demonstrates that our scheme can handle more than 525 encryption and (successful) decryption requests per second per core, which shows that it is lightweight and readily deployable in large-scale systems. Regarding security, our scheme also achieves a stronger soundness property, which puts less trust on the good behavior of the crypto server.
@inproceedings{DBLP:conf/uss/Lai0RCMS18,
author = {Russell W. F. Lai and
Christoph Egger and
Manuel Reinert and
Sherman S. M. Chow and
Matteo Maffei and
Dominique Schr{\"{o}}der},
editor = {William Enck and
Adrienne Porter Felt},
title = {Simple Password-Hardened Encryption Services},
booktitle = {27th {USENIX} Security Symposium, {USENIX} Security 2018, Baltimore,
MD, USA, August 15-17, 2018},
pages = {1405--1421},
publisher = {{USENIX} Association},
year = {2018},
url = {https://www.usenix.org/conference/usenixsecurity18/presentation/lai},
timestamp = {Mon, 01 Feb 2021 08:43:20 +0100},
biburl = {https://dblp.org/rec/conf/uss/Lai0RCMS18.bib},
bibsource = {dblp computer science bibliography, https://dblp.org}
}
Password remains the most widespread means of authentication, especially on the Internet. As such, it is the Achilles heel of many modern systems. Facebook pioneered using external cryptographic services to harden password-based authentication in a large scale. Everspaugh et al. (USENIX Security ’15) provided the first comprehensive treatment of such a service and proposed the PYTHIA PRF-Service as a cryptographically secure solution. Recently, Schneider et al. (ACM CCS ’16) proposed a more efficient solution which is secure in a weaker security model.
In this work, we show that the scheme of Schneider et al. is vulnerable to offline attacks just after a single validation query. Therefore, it defeats the purpose of using an external crypto service in the first place and it should not be used in practice. Our attacks do not contradict their security claims, but instead show that their definitions are simply too weak. We thus suggest stronger security definitions that cover these kinds of real-world attacks, and an even more efficient construction, PHOENIX, to achieve them. Our comprehensive evaluation confirms the practicability of PHOENIX: It can handle up to 50% more requests than the scheme of Schneider et al. and up to three times more than PYTHIA.
@inproceedings{DBLP:conf/uss/Lai0SC17,
author = {Russell W. F. Lai and
Christoph Egger and
Dominique Schr{\"{o}}der and
Sherman S. M. Chow},
editor = {Engin Kirda and
Thomas Ristenpart},
title = {Phoenix: Rebirth of a Cryptographic Password-Hardening Service},
booktitle = {26th {USENIX} Security Symposium, {USENIX} Security 2017, Vancouver,
BC, Canada, August 16-18, 2017},
pages = {899--916},
publisher = {{USENIX} Association},
year = {2017},
url = {https://www.usenix.org/conference/usenixsecurity17/technical-sessions/presentation/lai},
timestamp = {Mon, 01 Feb 2021 08:43:05 +0100},
biburl = {https://dblp.org/rec/conf/uss/Lai0SC17.bib},
bibsource = {dblp computer science bibliography, https://dblp.org}
}
@inproceedings{DBLP:conf/concur/HausmannSE16,
author = {Daniel Hausmann and
Lutz Schr{\"{o}}der and
Christoph Egger},
editor = {Jos{\'{e}}e Desharnais and
Radha Jagadeesan},
title = {Global Caching for the Alternation-free {\(\mu\)}-Calculus},
booktitle = {27th International Conference on Concurrency Theory, {CONCUR} 2016,
August 23-26, 2016, Qu{\'{e}}bec City, Canada},
series = {LIPIcs},
volume = {59},
pages = {34:1--34:15},
publisher = {Schloss Dagstuhl - Leibniz-Zentrum f{\"{u}}r Informatik},
year = {2016},
url = {https://doi.org/10.4230/LIPIcs.CONCUR.2016.34},
doi = {10.4230/LIPIcs.CONCUR.2016.34},
timestamp = {Sun, 25 Jul 2021 11:47:10 +0200},
biburl = {https://dblp.org/rec/conf/concur/HausmannSE16.bib},
bibsource = {dblp computer science bibliography, https://dblp.org}
}
@inproceedings{DBLP:conf/raid/EggerSKV13,
author = {Christoph Egger and
Johannes Schlumberger and
Christopher Kruegel and
Giovanni Vigna},
editor = {Salvatore J. Stolfo and
Angelos Stavrou and
Charles V. Wright},
title = {Practical Attacks against the {I2P} Network},
booktitle = {Research in Attacks, Intrusions, and Defenses - 16th International
Symposium, {RAID} 2013, Rodney Bay, St. Lucia, October 23-25, 2013.
Proceedings},
series = {Lecture Notes in Computer Science},
volume = {8145},
pages = {432--451},
publisher = {Springer},
year = {2013},
url = {https://doi.org/10.1007/978-3-642-41284-4\_22},
doi = {10.1007/978-3-642-41284-4\_22},
timestamp = {Tue, 14 May 2019 10:00:53 +0200},
biburl = {https://dblp.org/rec/conf/raid/EggerSKV13.bib},
bibsource = {dblp computer science bibliography, https://dblp.org}
}
System software, especially operating systems, tends to be highly configurable. Like every complex piece of software, a considerable amount of bugs in the implementation has to be expected. In order to improve the general code quality, tools for static analysis provide means to check for source code defects without having to run actual test cases on real hardware. Still, for proper type checking a specific configuration is required so that all header include paths are available and all types are properly resolved.
In order to find as many bugs as possible, usually a "full configuration" is used for the check. However, mainly because of alternative blocks in form of #else-blocks, a single configuration is insufficient to achieve full coverage. In this paper, we present a metric for configuration coverage (CC) and explain the challenges for (properly) calculating it. Furthermore, we present an efficient approach for determining a sufficiently small set of configurations that achieve (nearly) full coverage and evaluate it on a recent Linux kernel version.
@article{DBLP:journals/sigops/TartlerLDES11,
author = {Reinhard Tartler and
Daniel Lohmann and
Christian Dietrich and
Christoph Egger and
Julio Sincero},
title = {Configuration coverage in the analysis of large-scale system software},
journal = {{ACM} {SIGOPS} Oper. Syst. Rev.},
volume = {45},
number = {3},
pages = {10--14},
year = {2011},
url = {https://doi.org/10.1145/2094091.2094095},
doi = {10.1145/2094091.2094095},
timestamp = {Mon, 26 Oct 2020 08:24:58 +0100},
biburl = {https://dblp.org/rec/journals/sigops/TartlerLDES11.bib},
bibsource = {dblp computer science bibliography, https://dblp.org}
}
Thesis
Student Theses
- Julian Brost: "Threshold Password-Hardened Encryption" (FAU Master Thesis; with Dominique Schröder, Russell Lai)
- Kirthivaasan Puniamurthy: "A proof viewer for State-separating proofs" (Aalto Master Thesis; with Christopher Brzuska, Konrad Kohbrok, Sabine Oechsner)
Talks
FAUST Workshop Crypto Hacking
FAUST Workshop, GPN18, ICMP9
BGP und OSPF – wie das Internet funktioniert
frida – a Free Software Interactive Disassembler
DNSSEC
Debian -- jetzt auch ohne Linux