IACR News
Here you can see all recent updates to the IACR webpage. These updates are also available:
12 December 2023
Sulaiman Alhussaini, Craig Collett, Serge˘ı Sergeev
Céline Chevalier, Guirec Lebrun, Ange Martinelli
Most research on CGKAs has focused on how to improve these two security properties. However, post-compromise security and forward secrecy require the active participation of respectively all compromised users and all users within the group. Inactive users – who remain offline for long periods – do not update anymore their encryption keys and therefore represent a vulnerability for the entire group. This issue has already been identified in the MLS standard, but no solution, other than expelling these inactive users after some disconnection time, has been found.
We propose here a CGKA protocol based on TreeKEM and fully compatible with the MLS standard, that implements a “quarantine” mechanism for the inactive users in order to mitigate the risk induced by these users without removing them from the group. That mechanism indeed updates the inactive users’ encryption keys on their behalf and secures these keys with a secret sharing scheme. If some of the inactive users eventually reconnect, their quarantine stops and they are able to recover all the messages that were exchanged during their offline period. Our “Quarantined-TreeKEM” protocol thus offers a good trade-off between security and functionality, with a very limited – and sometimes negative – communication overhead.
François-Xavier Wicht, Zhipeng Wang, Duc V. Le, Christian Cachin
Cong Ling, Andrew Mendelsohn
11 December 2023
Technical University of Denmark, Dept. of Applied Mathematics and Computer Science, Copenagen Area
The goal of the project is to explore different routes towards providing a fully quantum-secure replacement for X3DH, the key exchange protocol used by Signal, WhatsApp and the likes. It is an excellent opportunity to be involved in advanced research on cryptographic systems secure against quantum computing.
For more information click the title of this job listing. If you are interested feel free to reach out to Christian Majenz (chmaj@dtu.dk).
Closing date for applications:
Contact: Christian Majenz, Associate Professor at DTU Compute, Cyber Security Engineering Section
More information: https://efzu.fa.em2.oraclecloud.com/hcmUI/CandidateExperience/en/sites/CX_1/job/2851/?utm_medium=jobshare
University of Kassel, Germany
The Information Security group is looking for a strong candidate to fill an open PhD position. The PhD will be supervised by Jiaxin Pan and will work on provable security, for instance, key exchange protocols and digital signature schemes. We will also work on the post-quantum security of them.
We hope that the PhD can publish at major venues, such as Crypto, Eurocrypt, Asiacrypt, PKC, etc., under the supervision. In the past, this has been successfully realized.
The position is paid according to EG13 TV-H (full-time). It is initially limited for 3 years with the possibility of extension for a further 2 years. The position comes with teaching load of 4 hours per week during the semester teaching period. This is usually manageable and can be done in the forms of tutorials, labs, seminars, or thesis co-supervision.
We encourage strong candidates with a Master degree and those who are close to finish to apply. Knowledge in post-quantum cryptography, digital signatures, or key exchange is highly desirable.
More information can be found in:
- https://stellen.uni-kassel.de/jobposting/9023eb9d3fd3366877c376079417eb1d088ded3c0 (English), or
- https://stellen.uni-kassel.de/jobposting/0870f187f0392f19987735519cbe2b5778a3eb910 (German)
Closing date for applications:
Contact: Jiaxin Pan: https://sites.google.com/view/jiaxinpan
More information: https://stellen.uni-kassel.de/jobposting/9023eb9d3fd3366877c376079417eb1d088ded3c0
University of Birmingham, UK
Closing date for applications:
Contact: Rishiraj Bhattacharyya (r.bhattacharyya@bham.ac.uk)
More information: https://edzz.fa.em3.oraclecloud.com/hcmUI/CandidateExperience/en/sites/CX_6001/job/3750/
Limitless Labs, Ukraine or Remote
This role is dedicated to applied research. In our initial phases, we are committed to understanding and leveraging the state-of-the-art, while in future phases, we will advance it. Primarily, the researcher will contribute to the design of new architectural solutions.
Responsibilities
- Design, specify and verify distributed systems by leveraging formal and experimental techniques.
- Build proof of concepts and prepare executable specifications for the development team.
- Regularly going through papers, bringing new ideas and staying up-to-date.
- Conducting theoretical and practical analysis of the performance of distributed systems.
- Collaborating with both internal and external contributors.
Closing date for applications:
Contact: Ira | Head of People @ Limitless Labs
More information: https://apply.workable.com/limitless-labs-network/j/EF6246F619/
Mingxun Zhou, Elaine Shi, Giulia Fanti
To address this challenge, we propose an efficient protocol called Shuffle-ZKP, which enables users within an unlinkable messaging system to collectively prove their compliance. Our protocol leverages a distributed and private set equality check protocol along with generic Non-Interactive Zero-Knowledge (NIZK) proof systems. We also provide an additional attributing protocol to identify misbehaving users. We theoretically analyze the protocol's correctness and privacy properties; we then implement and test it across multiple use cases. Our empirical results show that in use cases involving thousands of users, each user is able to generate a compliance proof within 0.2-10.6 seconds, depending on the use case, while the additional communication overhead remains under 3KB. Furthermore, the protocol is computationally efficient on the server side; the verification algorithm requires a few seconds to handle thousands of users in all of our use cases.
Tom Azoulay, Uri Carl, Ori Rottenstreich
Ori Mazor, Ori Rottenstreich
Sajin Sasy, Adithya Vadapalli, Ian Goldberg
Colin Putman, Keith M. Martin
Clément Hoffmann, Pierrick Méaux, François-Xavier Standaert
Yilei Chen, Jiatu Li
In this paper, we demonstrate, under plausible cryptographic assumptions, that both the range avoidance problem and the remote point problem cannot be efficiently solved by nondeterministic search algorithms, even when the input circuits are as simple as constant-depth circuits. This extends a hardness result established by Ilango, Li, and Williams (STOC '23) against deterministic algorithms employing witness encryption for $\textsf{NP}$, where the inputs to $\textsf{Avoid}$ are general Boolean circuits.
Our primary technical contribution is a novel construction of witness encryption inspired by public-key encryption for certain promise language in $\textsf{NP}$ that is unlikely to be $\textsf{NP}$-complete. We introduce a generic approach to transform a public-key encryption scheme with particular properties into a witness encryption scheme for a promise language related to the initial public-key encryption scheme. Based on this translation and variants of standard lattice-based or coding-based PKE schemes, we obtain, under plausible assumption, a provably secure witness encryption scheme for some promise language in $\textsf{NP}\setminus \textsf{coNP}_{/\textsf{poly}}$. Additionally, we show that our constructions of witness encryption are plausibly secure against nondeterministic adversaries under a generalized notion of security in the spirit of Rudich's super-bits (RANDOM '97), which is crucial for demonstrating the hardness of $\textsf{Avoid}$ and $\textsf{RPP}$ against nondeterministic algorithms.
Qi Pang, Jinhao Zhu, Helen Möllering, Wenting Zheng, Thomas Schneider
Daniel J. Bernstein
This paper shows that 1 contradicts 2 and that 1 contradicts 3: the existing heuristics imply that hybrid primal key-recovery attacks are exponentially faster than standard non-hybrid primal key-recovery attacks against the LPR PKE with any constant error width. This is the first report since 2015 of an exponential speedup in heuristic non-quantum primal attacks against non-ternary LPR.
Quantitatively, for dimension n, modulus n^{Q_0+o(1)}, and error width w, a surprisingly simple hybrid attack reduces heuristic costs from 2^{(ρ+o(1))n} to 2^{(ρ-ρ H_0+o(1))n}, where z_0=2Q_0/(Q_0+1/2)^2, ρ=z_0 log_4(3/2), and H_0=1/(1+(lg w)/0.057981z_0). This raises the questions of (1) what heuristic exponent is achieved by more sophisticated hybrid attacks and (2) what impact hybrid attacks have upon concrete cryptosystems whose security analyses have ignored hybrid attacks, such as Kyber-512.