Foundations of Cryptography

<!DOCTYPE html><html lang="en"><base href='https://foc.ethz.ch/'><meta charset='utf-8'> <meta name='viewport' content='width=device-width, initial-scale=1, user-scalable=no'> <meta name='mobile-web-app-capable' content='yes'> <meta name='apple-web-app-capable' content='yes'> <meta name='theme-color' content='#1F407A'>  <link rel='icon' href='./images/logos/logo.svg' type='image/svg+xml'> <link rel="manifest" href="./manifest.json"> <script src='./install-sw.js' async type='module'></script> <script src='./foc-elements/foc-card-section.js' async type='module'></script> <script src='./foc-elements/foc-card.js' async type='module'></script> <script src='./foc-elements/foc-list.js' async type='module'></script> <script src='./foc-elements/foc-publication-list.js' async type='module'></script> <script src='./foc-elements/foc-li.js' async type='module'></script> <script src='./foc-elements/foc-map.js' async type='module'></script> <link rel='stylesheet' type='text/css' href='./template.css'> <style> .timeline.animate:not(.rendering):not(.rendered) { display: none; } </style> <title>Foundations of Cryptography</title> <header> <a id="eth-logo" href="//ethz.ch"> <img src="//ethz.ch/etc/designs/ethz/img/header/ethz_logo_white.svg" alt="ETH Zürich" loading="lazy"> </a> <a class="foc-logo" href="//foc.ethz.ch"> <span> Foundations of Cryptography </span> <picture> <source srcset="./images/logos/logo-hor-wh.svg" media="(max-width: 680px)"> <img src="./images/logos/logo-wh.svg" alt="Foundations of Cryptography"> </picture> </a> </header> <nav> <a href='#news'>News</a> <a href='#group-picture'>People</a> <a href='#research'>Research</a> <a href='#teaching'>Teaching</a> </nav> <section id='news'> <h1>News</h1> <foc-list class='timeline'> <li is='foc-li' data-publication-src='./people/karenklein.json' data-publication-title='Tighter provable security for TreeKEM' data-publish-date='2025-03-18' data-image-src=''> Karen Azari and Andreas Ellison got a paper accepted at ACNS 2025. Congratulations! </li> <li is='foc-li' data-publication-src='./people/romanlangrehr.json' data-publication-title='Non-Interactive Key Exchange: New Notions, New Constructions, and Forward Security' data-publish-date='2025-02-06' data-image-src=''> Dennis Hofheinz and Roman Langrehr got a paper accepted at PKC 2025. Congratulations! </li> <li is='foc-li' data-publication-src='./people/karenklein.json' data-publication-title='Securely Instantiating Half Gates Garbling in the Standard Model' data-publish-date='2025-02-05' data-image-src=''> Karen Azari and Dennis Hofheinz got a paper accepted at PKC 2025. Congratulations! </li> <li is='foc-li' data-publication-src='./people/mariandietz.json' data-publication-title='How to Compress Garbled Circuit Input Labels, Efficiently' data-publish-date='2025-02-03' data-image-src=''> Marian Dietz got a paper accepted at EUROCRYPT 2025. Congratulations! </li> <li is='foc-li' data-publication-src='./people/romanlangrehr.json' data-publication-title='Malleable SNARKs and Their Applications' data-publish-date='2025-02-03' data-image-src=''> Dennis Hofheinz and Roman Langrehr got a paper accepted at EUROCRYPT 2025. Congratulations! </li> <li is='foc-li' data-publication-src='./people/karenklein.json' data-publication-title='On the Adaptive Security of Free-XOR-based Garbling Schemes in the Plain Model' data-publish-date='2025-02-01' data-image-src=''> Karen Azari got a paper accepted at EUROCRYPT 2025. Congratulations! </li> <li is='foc-li' data-publication-src='./people/ceciliaboschini.json' data-publication-title='Ringtail: Practical Two-Round Threshold Signatures from Learning with Errors' data-publish-date='2024-10-08' data-image-src=''> Cecilia Boschini got a paper accepted at the IEEE Symposium on Security and Privacy 2025. Congratulations! </li> <li is='foc-li' data-publication-src='./people/karenklein.json' data-publication-title='DeCAF: Decentralizable Continuous Group Key Agreement with Fast Healing' data-publish-date='2024-10-07' data-image-src=''> Karen Klein got a paper accepted at SCN 2024. Congratulations! </li> <li is='foc-li' data-publication-src='./people/romanlangrehr.json' data-publication-title='On the Black-Box Complexity of Private-Key Inner-Product Functional Encryption' data-publish-date='2024-10-07' data-image-src=''> Roman Langrehr got a paper accepted at TCC 2024. Congratulations! </li> <li is='foc-li' data-title='Visitor' data-publish-date='2024-10-07' data-image-src=''> Milan Gonzalez-Thauvin is visiting from 07.09.2024-07.02.2025 Welcome Milan! </li> <li is='foc-li' data-publication-src='./people/michaelklooss.json' data-publication-title='Practical Blind Signatures in Pairing-Free Groups' data-publish-date='2024-10-07' data-image-src=''> Michael Klooss and Michael Reichle got a paper accepted at ASIACRYPT 2024. Congratulations! </li> <li is='foc-li' data-publication-src='./people/michaelklooss.json' data-publication-title='RoK, Paper, SISsors – Toolkit for Lattice-based Succinct Arguments' data-publish-date='2024-10-07' data-image-src=''> Michael Klooss got a paper accepted at ASIACRYPT 2024. Congratulations! </li> <li is='foc-li' data-publication-src='./people/nicholasbrandt.json' data-publication-title='Lower Bounds for Levin–Kolmogorov Complexity' data-publish-date='2024-10-03' data-image-src=''> Nicholas Brandt got a paper accepted at TCC 2024. Congratulations! </li> <li is='foc-li' data-publication-src='./people/michaelreichle.json' data-publication-title='Adaptively Secure 5 Round Threshold Signatures from MLWE/MSIS and DL with Rewinding' data-publish-date='2024-05-07' data-image-src=''> Michael Reichle got a paper accepted at CRYPTO 2024. Congratulations! </li> <li is='foc-li' data-publication-src='./people/ceciliaboschini.json' data-publication-title='That’s not my signature! Fail-stop signatures for a post-quantum world' data-publish-date='2024-05-07' data-image-src=''> Cecilia Boschini got a paper accepted at CRYPTO 2024. Congratulations! </li> <li is='foc-li' data-publication-src='./people/juliakastner.json' data-publication-title='Pairing-Free Blind Signatures from Standard Assumptions in the ROM' data-publish-date='2024-05-07' data-image-src=''> Julia Kastner and Michael Reichle got a paper accepted at CRYPTO 2024. Congratulations! </li> <li is='foc-li' data-publication-src='./people/michaelreichle.json' data-publication-title='Breaking Parallel ROS: Implication for Isogeny and Lattice-based Blind Signatures' data-publish-date='2024-01-15' data-image-src=''> Michael Reichle got a paper accepted at PKC 2024. Congratulations! </li> <li is='foc-li' data-publication-src='./people/romanlangrehr.json' data-publication-title='On Structure-Preserving Cryptography and Lattices' data-publish-date='2023-12-22' data-image-src=''> Dennis Hofheinz, Kristina Hostáková, Roman Langrehr, and Bogdan Ursu got a paper accepted at PKC 2024. Congratulations! </li> <li is='foc-li' data-publication-src='./people/juliakastner.json' data-publication-title='Compact Lossy Trapdoor Functions and Selective Opening Security From LWE' data-publish-date='2023-12-22' data-image-src=''> Dennis Hofheinz, Kristina Hostáková, Julia Kastner, Karen Klein, and Akin Ünal got a paper accepted at PKC 2024. Congratulations! </li> <li is='foc-li' data-publication-src='./people/romanlangrehr.json' data-publication-title='On the Multi-User Security of LWE-based NIKE' data-publish-date='2023-09-13' data-image-src=''> Roman Langrehr got a paper accepted at TCC 2023. Congratulations! </li> <li is='foc-li' data-title='Paper accepted' data-publication-src='./people/kristinahostakova.json' data-publication-title='Generalized Fuzzy Password-Authenticated Key Exchange from Error Correcting Codes' data-publish-date='2023-09-06' data-image-src=''> Sebastian Faller and Kristina Hostáková got a paper accepted at ASIACRYPT 2023. Congratulations! </li> <li is='foc-li' data-title='Paper accepted' data-publication-src='./people/juliakastner.json' data-publication-title='Concurrent Security of Anonymous Credentials Light, Revisited' data-publish-date='2023-09-04' data-image-src=''> Julia Kastner got a paper accepted at ACM CCS 2023. Congratulations! </li> <li is='foc-li' data-title='Visitor' data-publish-date='2023-08-1' data-image-src=''> Michael Klooß is visiting from 7.08.-11.08. Welcome Michael! </li> <li is='foc-li' data-title='Visitor' data-publish-date='2023-07-1' data-image-src=''> Thomas Attema is visiting from 10.07.-11.08. Welcome Thomas! </li> <li is='foc-li' data-title='Visitors' data-publish-date='2023-05-30' data-image-src=''> Adam O'Neill and Ojaswi Acharya are visiting from 30.05.-3.06. Welcome Adam and Ojaswi! </li> <li is='foc-li' data-title='🏆 VIS Teaching Awards' data-publish-date='2023-05-25' data-image-src=''> The Information Security lecture (co-held with the Information Security Group) was awarded the VIS Teaching Award for Best Interaction. Congratulations! </li> <li is='foc-li' data-title='Paper accepted' data-publication-src='./people/sebastianfaller.json' data-publication-title='Security Analysis of the WhatsApp End-to-End Encrypted Backup Protocol' data-publish-date='2023-05-08' data-image-src=''> Sebastian Faller got a paper accepted at CRYPTO 2023. Congratulations! </li> <li is='foc-li' data-title='Paper accepted' data-publication-src='./people/juliakastner.json' data-publication-title='The Power of Undirected Rewindings for Adaptive Security' data-publish-date='2023-05-08' data-image-src=''> Dennis Hofheinz, Julia Kastner, and Karen Klein got a paper accepted at CRYPTO 2023. Congratulations! </li> <li is='foc-li' data-title='🏆 Early Career Best Paper Award' data-image-src='./images/news/ec23awardCropped.png' data-publish-date='2023-05-03'> Akin Ünal won the Early Career Best Paper Award at EUROCRYPT 2023 with his paper "Worst-Case Subexponential Attacks on PRGs of Constant Degree or Constant Locality". Congratulations Akin! </li> <li is='foc-li' data-title='🎓 Bogdan Ursu graduated' data-image-src='' data-publish-date='2023-03-29'> Bogdan Ursu graduated with his thesis titled "New Constructions of Round-Efficient Zero-Knowledge Proofs". Congratulations Bogdan! </li> <li is='foc-li' data-title='Paper accepted' data-publication-src='./people/dennishofheinz.json' data-publication-title='Almost Tightly-Secure Re-Randomizable and Replayable CCA-secure Public Key Encryption' data-publish-date='2023-02-12' data-image-src=''> Dennis Hofheinz got a paper accepted at PKC 2023. Congratulations! </li> <li is='foc-li' data-title='Paper accepted' data-publication-src='./people/suvradipchakraborty.json' data-publication-title='Deniable Authentication when Signing Keys Leak' data-publish-date='2023-02-02' data-image-src=''> Dennis Hofheinz and Suvradip Chakraborty got a paper accepted at EUROCRYPT 2023. Congratulations! </li> <li is='foc-li' data-title='Paper accepted' data-publication-src='./people/suvradipchakraborty.json' data-publication-title='Reverse Firewalls for Oblivious Transfer Extension and Applications to Zero-Knowledge' data-publish-date='2023-02-02' data-image-src=''> Suvradip Chakraborty got a paper accepted at EUROCRYPT 2023. Congratulations! </li> <li is='foc-li' data-title='Paper accepted' data-publication-src='./people/akinuenal.json' data-publication-title='Worst-Case Subexponential Attacks on PRGs of Constant Degree or Constant Locality' data-publish-date='2023-02-02' data-image-src=''> Akin Ünal got a paper accepted at EUROCRYPT 2023. Congratulations! </li> <li is='foc-li' data-publication-src='./people/nicholasbrandt.json' data-publication-title='On the Correlation Complexity of MPC with Cheater Identification' data-publish-date='2023-02-01' data-image-src=''> Nicholas Brandt got a paper accepted at Financial Crypto 2023. Congratulations! </li> <li is='foc-li' data-title='Visitor' data-publish-date='2022-11-25' data-image-src=''> Michael Reichle is visiting from 12.12.-15.12. Welcome Michael! </li> <li is='foc-li' data-title='Visitor' data-publish-date='2022-11-25' data-image-src=''> Erkan Tairi is visiting from 28.11.-2.12. Welcome Erkan! </li> <li is='foc-li' data-title='Visitor' data-publish-date='2022-09-21' data-image-src=''> Christoph Striecks is visiting from 19.9.-23.9. Welcome Christoph! </li> <li is='foc-li' data-publication-src='./people/karenklein.json' data-publication-title='SNACKs: Leveraging Proofs of Sequential Work for Blockchain Light Clients' data-publish-date='2022-09-14' data-image-src=''> Karen Klein got a paper accepted at ASIACRYPT 2022. Congratulations! </li> <li is='foc-li' data-title='Visitor' data-publish-date='2022-08-31' data-image-src=''> Thomas Attema is visiting from 12.9.-16.9. Welcome Thomas! </li> <li is='foc-li' data-title='Visitor' data-publish-date='2022-08-31' data-image-src=''> David Niehues is visiting from 5.9.-9.9. Welcome David! </li> <li is='foc-li' data-publication-src='./people/juliakastner.json' data-publication-title='The Abe-Okamoto Partially Blind Signature Scheme Revisited' data-publish-date='2022-08-31' data-image-src=''> Julia Kastner got a paper accepted at ASIACRYPT 2022. Congratulations! </li> <li is='foc-li' data-publication-src='./people/juliakastner.json' data-publication-title='The Price of Verifiability: Lower Bounds for Verifiable Random Functions' data-publish-date='2022-08-31' data-image-src=''> Nicholas Brandt, Dennis Hofheinz, Julia Kastner, and Akin Ünal got a paper accepted at TCC 2022. Congratulations! </li>  </foc-list> </section> <section id='group-picture' class='image-container'> <img srcset="./images/group-photo-480px.webp 480w, ./images/group-photo-1280px.webp 1280w, ./images/group-photo.webp 1709w" loading="lazy" alt="Photograph of the group in front of the CAB building" sizes="calc(60vw + 120px)"> </section> <section id='people' class='tiles'>  <div> <foc-card-section> <h2 slot='prefix'>Professor</h2> <foc-card data-src='./people/dennishofheinz.json'></foc-card> </foc-card-section> <foc-card-section> <h2 slot='prefix'>Administration</h2> <foc-card data-src='./people/claudiaguenthart.json'></foc-card> </foc-card-section> </div> <foc-card-section> <h2 slot='prefix'>PostDocs</h2> <foc-card data-src='./people/ceciliaboschini.json'></foc-card> <foc-card data-src='./people/kristinahostakova.json'></foc-card> <foc-card data-src='./people/karenklein.json'></foc-card> <foc-card data-src='./people/michaelklooss.json'></foc-card> <foc-card data-src='./people/michaelreichle.json'></foc-card> </foc-card-section> <foc-card-section> <h2 slot='prefix'>PhD Students</h2> <foc-card data-src='./people/nicholasbrandt.json'></foc-card> <foc-card data-src='./people/mariandietz.json'></foc-card> <foc-card data-src='./people/xiaoqiduan.json'></foc-card> <foc-card data-src='./people/sebastianfaller.json'></foc-card> <foc-card data-src='./people/romanlangrehr.json'></foc-card> <foc-card data-src='./people/moetosuzuki.json'></foc-card> </foc-card-section> <foc-card-section> <h2 slot='prefix'>Alumni</h2> <foc-card data-src='./people/bogdanursu.json'></foc-card> <foc-card data-src='./people/suvradipchakraborty.json'></foc-card> <foc-card data-src='./people/khanhnguyen.json'></foc-card> <foc-card data-src='./people/akinuenal.json'></foc-card> <foc-card data-src='./people/juliakastner.json'></foc-card> </foc-card-section> </section> <section id='research'> <h1>Research</h1> <h3>Motivation.</h3> <p> Cryptography is a crucial tool for securing information systems. Cryptographic building blocks ensure the secrecy and integrity of information, and help to protect the privacy of users. Still, most actually deployed cryptographic schemes are not known to have any rigorously proven security guarantees. This has led to a number of far-reaching security issues in widely deployed software systems. </p> <h3>Goal.</h3> <p> Our goal is to provide practical cryptographic building blocks that come with rigorously proven security guarantees. These building blocks should be efficient enough for the use in large-scale modern information systems, and their security should be defined and formally analyzed in a mathematically rigorous manner. </p> <h3>Technical interests.</h3> <p> We are interested in the foundations of theoretical cryptography, and in general ways to derive constructions and security guarantees in a modular fashion. One research focus in our group concerns new cryptographic building blocks such as indistinguishability obfuscation, functional encryption, and fully homomorphic encryption. We are particularly interested in the design and analysis of cryptographic schemes in the public-key setting. This covers common tools like public-key encryption and digital signatures, specifically in realistic modern scenarios (such as settings with adaptive adversaries, and a huge number of users). </p> </section> <section id='teaching' class='tiles'> <h1>Teaching</h1> <foc-card-section> <foc-card> <div class='name'>Lecture: Digital Signatures</div> <p> This information concerns the “Digital Signatures” lecture in the Spring 2023 semester at ETH. The content for this course will be provided through Moodle. </p> </foc-card> <foc-card> <div class='name'>Lecture: Information Security</div> <p> This information concerns the “Information Security” lecture in the Spring 2023 semester at ETH. The content for this course will be provided through Moodle. </p> </foc-card> <foc-card> <div class='name'>Seminar: Current Topics in Cryptography</div> <p> Information about the course will be communicate to the subscribed participants via email. </p> </foc-card> </foc-card-section> <foc-card-section> <h2 slot='prefix'>Available Theses</h2> <div slot='prefix' style='margin: 20px 0'> For more details or questions in general please contact <a href='mailto:michael.reichle@inf.ethz.ch?subject=Thesis'>michael.reichle@inf.ethz.ch</a>. </div> <foc-card> <div class='name'>Improving the Security of Lattice-based Threshold Signatures(Master Thesis)</div> <p> A <i>t-out-of-N threshold signature</i> distributes a secret key among N parties, such that any group of at least t parties can jointly produce a valid siganture. Importantly, even if up to t-1 parties are corrupted, an adversary still cannot forge signatures. Threshold signatures have practical applications, such as blockchain systems. Recently, NIST has launched a standardization effort <a href='https://doi.org/10.6028/NIST.IR.8214C.ipd'> [1]</a> for multi-party threshold protocols. <br> While there are efficient constructions with strong security guarantees in the classical (pre-quantum) settings, research on post-quantum (in particular, lattice-based) threshold signatures remains limited (see e.g. <a href='https://eprint.iacr.org/2024/184'>[2]</a>), and many existing constructions provide only weak security guarantees. <br> The aim of this project is to enhance the security guarantees of existing lattice-based threshold signatures. In particular, the project will focus on applying existing technique for distributed key generation and for adaptive security to existing lattice-based constructions to enhance their security guarantees. A student interested in this thesis should have a background in crytography (Information Security course, Digital Signature course, etc.) and basic knowledge of mathematics </p> <div class='references'> <ul> <li> <a href='https://doi.org/10.6028/NIST.IR.8214C.ipd'> [1] NIST first call for Multi-Party Threshold Schemes </a> <a href='https://eprint.iacr.org/2024/184'> [2] Threshold Raccoon: Practical Threshold Signatures from Standard Lattice Assumptions </a> </li> </ul> </div> <a class='mail' href='mailto:moeto.suzuki@inf.ethz.ch'>Moeto Suzuki</a> </foc-card>       </foc-card-section> </section> <section id='contact' class='tiles'> <foc-card> <div class='name'> <img src="./images/logos/logo.svg" alt="Foundations of Cryptography"> <span>Contact</span> </div> <a class="address" href="https://goo.gl/maps/MibPzU5TdU3iYU3B7"> <span> Universitaetstrasse 6 <br> CAB Building, H Floor <br> 8092 Zurich <br> Switzerland </span> </a> <a class='mail' href='mailto:claudia.guenthart@inf.ethz.ch'>claudia.guenthart@inf.ethz.ch</a> <a class='homepage' href='//foc.ethz.ch/'>foc.ethz.ch</a> </foc-card> </section> <footer> <div class='spacer'></div> <section class='contact tiles'> <h2> Contact </h2> <foc-card> <div class='foc-logo' class='name'> <picture> <img src="./images/logos/logo.svg" alt="Foundations of Cryptography"> </picture> <span> Foundations of Cryptography </span> </div> <a class="address" href="https://goo.gl/maps/MibPzU5TdU3iYU3B7"> <span> Universitaetstrasse 6 <br> CAB Building, H Floor <br> 8092 Zurich <br> Switzerland </span> </a> <a class='mail' href='mailto:claudia.guenthart@inf.ethz.ch'>claudia.guenthart@inf.ethz.ch</a> <a class='homepage' href='//foc.ethz.ch/'>foc.ethz.ch</a> </foc-card> </section> <foc-map data-src='https://www.google.com/maps/embed?pb=!1m14!1m8!1m3!1d983.1914598703298!2d8.547943600718801!3d47.378403662217615!3m2!1i1024!2i768!4f13.1!3m3!1m2!1s0x0%3A0x965279ae5b0d4afd!2sETH%20Department%20of%20Computer%20Science!5e0!3m2!1sen!2sch!4v1657097257268!5m2!1sen!2sch'></foc-map> <section class='band'> <h2>Affiliations</h2> <foc-list class='timeline'> <li> <a href='//ti.ethz.ch/'>Institute of Theoretical Computer Science</a> </li> <li> <a href='//inf.ethz.ch/'>Department of Computer Science</a> </li> <li> <a href='//ethz.ch/'>ETH Zürich</a> </li> </foc-list> </section> <div> <div> <a href='/imprint.html'>Imprint</a> </div> <a href='//ethz.ch/en/footer/disclaimer.html'>Disclaimer</a> <a href='//ethz.ch/en/footer/data-protection.html'>Data protection</a> <a href='//ethz.ch/'>© 2022 ETH Zürich</a> <div> </footer></html>

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Foundations of Cryptography