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Special Topics on Privacy and Public Auditability — Event 7

Featured topics: Timelock Encryption, Witness Encryption, Deniable Encryption.

Structure: Welcome/introduction; two invited talks; break; one invited talk and a panel conversation.

Date and time: January 16th, 2025, 12:00–16:00 EST (UTC -5). (Subject to modifications)

Location: Virtual event (video conference).

Attendance: Open and free to the public, upon registration.

Format: Webinar (presenters can share video and audio; attendees can use text for questions and comments).

STPPA7 Schedule:

Times displayed in EST = UTC-5 (EST = Eastern Standard Time; UTC = Coordinated Universal Time)

Abbreviated bios of the invited speakers:

(Based on text provided by the speakers/panelists, with possible adaptations/abbreviations for conciseness and consistency; see possible links for extended bios)

  • Sanjam Garg is an Associate Professor at the University of California, Berkeley. His research interests are in cryptography and its applications to security and privacy. He obtained his Ph.D. from the University of California, Los Angeles in 2013 and his undergraduate degree from the Indian Institute of Technology, Delhi in 2008. Prof. Garg is the recipient of various honors such as the ACM Doctoral Dissertation Award, the Sloan Research Fellowship and the IIT Delhi Graduates of the Last Decade Award. Prof. Garg's research has been recognized with a test of time award at FOCS 2023, and best paper awards at EUROCRYPT 2013, CRYPTO 2017 and EUROCRYPT 2018.
  • Kelsey Melissaris is a postdoctoral researcher in Aarhus University’s Cryptography and Security Group. Her postdoctoral research is focused on digital signatures and threshold cryptography. Kelsey received her Ph.D. from the City University of New York in 2022 and wrote her thesis on authenticated key exchange.
  • Rafail Ostrovsky is the Chair in Knowledge Sciences at UCLA Samueli School of Engineering. He is a Distinguished Professor of Computer Science and Mathematics at UCLA, and is serving on the editorial boards of Journal of ACM, Algorithmica Journal, and Journal of Cryptology. He is a Fellow of the NAI, AAAS, ACM, IEEE, and IACR, and foreign member of Academia Europaea. He has 350+ refereed publications and 15 issued USPTO patents. He chaired the IEEE TC on Mathematical Foundations of Computing (2015–2018), chaired the FOCS 2011 PC, and served on 40+ international conference PC's. He earned multiple honors, including the Henry Taub Prize (1993), the RSA prize (2018), and two distinguished awards from IEEE Computer Society (2017, 2022).
  • Yolan Romailler is an applied cryptographer at Randamu delving into (and dwelling on) cryptography, secure coding, and other fun things. He has previously spoken at Black Hat USA, Real World Crypto and DEF CON on topics including automation in cryptography research, functional encryption, distributed randomness, and more! He notably introduced the first practical fault attack against the EdDSA signature scheme. Nowadays he's working on threshold cryptography, including Verifiable Random Functions (VRFs), Verifiable Delay Functions (VDFs), distributed key generation, and timelock encryption.

Organization: The STPPA series is hosted by the NIST Privacy-Enhancing Cryptography (PEC) project. The PEC team (Luís Brandão, Angela Robinson, René Peralta) and all speakers (mentioned above) participated in the panel conversation. Angela Robinson introduced two talks/speakers. The STPPA7 event was organized by Luís Brandão, who also opened the event and introduced one talk/speaker. The virtual event (webinar) received around 215 registrations, of which around 115 attended at least 30 minutes, and around 90 attended more than 90 minutes.

About STPPA: In the "Special Topics on Privacy and Public Auditability" series, the NIST privacy-enhancing cryptography (PEC) project hosts talks on various interconnected topics related to privacy and public auditability. A main goal of the STPPA series is to gather reference material about "PEC tools", which may facilitate future reflections on aspects of standardization and of development of recommendations/guidelines about advanced cryptography, namely for uses related to privacy and public auditability. Each event intends to convey basic technical background, incite curiosity, suggest research questions and discuss applications, with an emphasis on the role of cryptographic tools. 

Code of conduct: Attending an STPPA event requires abiding to the Code of Conduct for NIST Conferences.

Selected Presentations
January 16, 2025 Type
12:00 PM STPPA #7 Welcome and Introduction

Abstract. Welcome to STPPA#7: the 7th event of the Special Topics on Privacy and Public Auditability (STPPA)! This event explores the theme of "Special Types of Encryption", with talks on timelock encryption, witness encryption, deniable encryption and functional encryption. This brief talk opens the event, introduces the context of the hosting "Privacy Enhancing Cryptography" (PEC) project, welcomes the speakers, and presents the schedule.

Slide cover: STPPA7 intro

Presentation
12:15 PM Timelock Encryption: an Overview and Retrospective
Kelsey Melissaris - Aarhus University (Denmark)
Yolan Romailler - Randamu Inc (Switzerland and USA)

Abstract. This talk presents an overview of timelock encryption (TLE), a cryptographic primitive which secures messages until some point in the future specified during encryption. We review definitions, motivations, applications, and discuss trade offs between two popular timelocking techniques: puzzle-based and authority-based. We then present an authority-based TLE from the identity-based encryption (IBE) scheme of Boneh and Franklin, which is in turn constructed from BLS signatures. Our instantiation leverages threshold BLS to replace the trusted IBE authority with a network of parties, each of whom is potentially malicious. The accompanying implementation is built upon the League of Entropy, a threshold network that acts as our decentralized authority via its public randomness beacon service. The details of this TLE construction and implementation are provided. Finally, in retrospect, we discuss the practical challenges of this implementation and address relevant standardization efforts. We also briefly mention our ongoing work to efficiently boost the applicability of this TLE scheme.

Joint work with Nicolas Gailly (Lagrange Labs)

Suggested readings: ia.cr/2023/189

Slide cover: STPPA7 timelock encryption

Presentation
1:00 PM Witness Encryption: Theory and Practice
Sanjam Garg - University of California, Berkeley (USA)

Abstract. In this talk, I will introduce the notion of Witness Encryption and discuss known general constructions. Next, I will discuss efficient special-purpose witness encryption schemes and their applications.

Joint work with Chongwon Cho, Nico Döttling, Sanjam Garg, Craig Gentry, Divya Gupta, Mohammad Hajiabadi, Yuval Ishai, Giulio Malavolta,Peihan Miao, Tamer Mour, Rafail Ostrovsky, Antigoni Polychroniadou, Amit Sahai, Akshayaram Srinivasan, and Brent Waters

Suggested readings: ia.cr/2013/258

Slide cover: STPPA7 witness encryption

Presentation
2:30 PM The Multiple Faces of Deniability
Rafail Ostrovsky - UCLA (USA)

Abstract. I will survey multiple aspects of deniability and related cryptographic notions, including the original deniable encryption paper of Canetti, Dwork, Naor, and Ostrovsky from 1996 and some of the follow-up works on deniable encryption. I will also discuss several related cryptographic notions and how they differ from deniable encryptions. These notions include equivocal encryption and equivocal commitment and their applications in cryptography. Specifically, I will describe applications to non-malleability and adaptive garbling. Finally, I will discuss a related concept of covert multi-party computation and how to construct it.

Suggested readings. DOI:10.1007/BFb0052229

Slide cover: STPPA7 deniable encryption

Presentation
3:15 PM STPPA7 Panel

Abstract. This will be an informal panel conversation, with the STPPA7 speakers of the talks on timelock encryption, witness encryption, deniable encryption and functional encryption. The panel will reflect on the possible uses of these special types of encryption, and advanced cryptography in general, with a particular emphasis on goals of privacy and public auditability. The reflection will extend to considerations about opportunities, challenges, and visions for the future.

slide: STPPA panel questions

Presentation

Event Details

Starts: January 16, 2025 - 12:00 PM EST
Ends: January 16, 2025 - 04:00 PM EST

Format: Virtual Type: Webinar

Attendance Type: Open to public
Audience Type: Industry,Government,Academia,Other

Parent Project

See: Privacy-Enhancing Cryptography

Related Topics

Security and Privacy: cryptography

Created November 01, 2024, Updated January 23, 2025