IACR News
Here you can see all recent updates to the IACR webpage. These updates are also available:
15 December 2020
Ant Group
Candidates are expected to be developing cryptographic libraries and/or conduct related researches with a growing team of researchers and engineers. Candidates are likely to be working in one of the following directions:
- homomorphic encryptions
- multiparty computations
- zero-knowledge proofs
Bonus points:
- experience in developing cryptographic libraries
- top tier publications in cryptography or security
- experience with Rust
- Beijing
- Hangzhou
Closing date for applications:
Contact: Zhenfei Zhang
Max Plank Institutes in Computer Science, Germany
The Max Planck Institutes for Informatics (Saarbruecken), Software Systems (Saarbruecken and Kaiserslautern), and Security and Privacy (Bochum) offer research internships in all areas of Computer Science. An internship at a Max Planck Institute is a way to pursue world-class research in computer science! Our internships are also an excellent way to explore research or new research areas for the first time.
Internships are open to exceptional Bachelors, Masters, and Doctoral students worldwide, as well as exceptional individuals from industry interested in gaining academic research experience in computer science. Intern positions are limited and admissions are very competitive
We welcome interns all year round, but most interns prefer the summer months. Every intern works directly with an assigned faculty mentor at one of the participating institutes. Internship projects are based on the intern’s academic interests, maturity and prior experience.
All interns receive a monthly stipend, free (shared) housing, and travel to- and from- the institute hosting the internship. A typical internship lasts 12 to 14 weeks, but longer internships are possible.
Application Deadlines for Summer Internships:
- Early Deadline: 31 December (for internships starting in May or June)
- Late Deadline: 31 January (for internships starting in July or August)
More information can be obtained at https://www.cis.mpg.de/internships
We understand that travel restrictions due to the ongoing COVID-19 pandemic may prevent interns from traveling to host institutes right now. In such a case, the intern and the mentor may agree mutually to complete the internship remotely. The intern will still be paid the monthly stipend.
Closing date for applications:
Contact: Catalin Hritcu
More information: https://www.cis.mpg.de/internships
14 December 2020
Prasanna Ravi, Shivam Bhasin, Sujoy Sinha Roy, Anupam Chattopadhyay
Thomas Pornin
- Element encoding is canonical, and verified upon decoding. For a 2n-bit group (with n-bit security), encoding size is 2n + 1 bits, i.e. as good as compressed points on classic prime order curves.
- Unified and complete formulas allow secure and efficient computations in the group.
- Efficiency is on par with twisted Edwards curves, and in some respects slightly better; e.g. half of double-odd curves have formulas for computing point doublings with only six multiplications (down to 1M+5S per doubling on some curves).
We describe here various formulas and discuss implementations. We also define two specific parameter choices for curves with 128-bit security, called do255e and do255s. Our own implementations on 64-bit x86 (Coffee Lake) and low-end ARM Cortex M0+ achieve generic point multiplication in 76696 and 2.19 million cycles, respectively, with curve do255e.
Javad Doliskani
13 December 2020
Daniel Escudero, Anders Dalskov
Siyao Guo, Pritish Kamath, Alon Rosen, Katerina Sotiraki
We study the possibility of designing non-interactive LWE-based protocols with polynomial LWE-modulus. To this end,
We identify and formalize simple non-interactive and polynomial LWE-modulus variants of existing protocols, where Alice and Bob simultaneously exchange one or more (ring) LWE samples with polynomial LWE-modulus and then run individual key reconciliation functions to obtain the shared key.
We point out central barriers and show that such non-interactive key-exchange protocols are impossible if:
1) the reconciliation functions first compute the inner product of the received LWE sample with their private LWE secret. This impossibility is information theoretic.
2) one of the reconciliation functions does not depend on the error of the transmitted LWE sample. This impossibility assumes hardness of LWE.
We give further evidence that progress in either direction, of giving an LWE-based NIKE protocol or proving impossibility of one will lead to progress on some other well-studied questions in cryptography.
Overall, our results show possibilities and challenges in designing simple (ring) LWE-based non-interactive key exchange protocols.
Xiaolu Hou, Jakub Breier, Shivam Bhasin
In this paper, we target a specific bit permutation vulnerability in the block cipher GIFT that allows the attacker to mount a key recovery attack. We present a novel SCA methodology called DCSCA - Differential Ciphertext SCA, which follows principles of differential fault analysis, but instead of the usage of faults, it utilizes SCA and statistical distribution of intermediate values. We simulate the attack on a publicly available bitslice implementation of GIFT, showing the practicality of the attack. We further show the application of the attack on GIFT-based AEAD schemes (GIFT-COFB, ESTATE, HYENA, and SUNDAE-GIFT) proposed for the NIST LWC competition. DCSCA can recover the master key with $2^{13.39}$ AEAD sessions, assuming 32 encryptions per session.
Arian Arabnouri, Reza Ebrahimi Atani, Shiva Azizzadeh
Julian Brost, Christoph Egger, Russell W. F. Lai, Fritz Schmid, Dominique Schröder, Markus Zoppelt
While PHE significantly strengthens data security, it introduces a single point of failure because key-derivation always requires access to the crypto service. In this work, we address this issue and simultaneously increase security by introducing threshold password-hardened encryption. Our formalization of this primitive revealed shortcomings of the original PHE definition that we also address in this work. Following the spirit of prior works, we give a simple and efficient construction using lightweight tools only. We also implement our construction and evaluate its efficiency. Our experiments confirm the practical efficiency of our scheme and show that it is more efficient than common memory-hard functions, such as scrypt. From a practical perspective this means that threshold PHE can be used as an alternative to scrypt for password protection and key-derivation, offering better security in terms of offline brute force attacks.
Sherman S. M. Chow, Katharina Fech, Russell W. F. Lai, Giulio Malavolta
MCORAM not only provides an alternative solution to private anonymous data access (Eurocrypt 2019) but also serves as a promising building block for equipping oblivious file systems with access control and extending other advanced cryptosystems to the multi-client setting.
Despite being a powerful object, the current state-of-the-art is unsatisfactory: The only existing scheme requires $O(\sqrt n)$ communication and client computation for a database of size $n$. Whether it is possible to reduce these complexities to $\mathsf{polylog}(n)$, thereby matching the upper bounds for ORAM, is an open problem, i.e., can we enjoy access control and client-obliviousness under the same bounds?
Our first result answers the above question affirmatively by giving a construction from fully homomorphic encryption (FHE). Our main technical innovation is a new technique for cross-key trial evaluation of ciphertexts.
We also consider the same question in the setting with $N$ non-colluding servers, out of which at most $t$ of them can be corrupt. We build multi-server MCORAM from distributed point functions (DPF), and propose new constructions of DPF via a virtualization technique with bootstrapping, assuming the existence of homomorphic secret sharing and pseudorandom generators in NC0, which are not known to imply FHE.
Viktoria Ronge, Christoph Egger, Russell W. F. Lai, Dominique Schröder, Hoover H. F. Yin
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, in the sense that 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.
Yongwoo Lee, Joonwoo Lee, Young-Sik Kim, HyungChul Kang, Jong-Seon No
Valerio Cini, Sebastian Ramacher, Daniel Slamanig, Christoph Striecks
In this work, we study the setting of generically transforming PKE schemes with potentially large, i.e., non-negligible, correctness error to ones having negligible correctness error. While there have been previous treatments in an asymptotic setting by Dwork, Naor, and Reingold (EUROCRYPT 2004), our goal is to come up with practically efficient compilers in a concrete setting and apply them in two different contexts. Firstly, we show how to generically transform weakly secure deterministic or randomized PKEs into CCA-secure KEMs in the (Q)ROM using variants of HHK. This applies to essentially all candidates to the NIST PQC based on lattices and codes with non-negligible error for which we provide an extensive analysis. We thereby show that it improves some of the code-based candidates. Secondly, we study puncturable KEMs in terms of the Bloom Filter KEM (BFKEM) proposed by Derler et al. (EUROCRYPT 2018) which inherently have a non-negligible correctness error. BFKEMs are a building block to construct fully forward-secret zero round-trip time (0-RTT) key-exchange protocols. In particular, we show the first approach towards post-quantum secure BFKEMs generically from lattices and codes by applying our techniques to identity-based encryption (IBE) schemes with (non-)negligible correctness error.
Ariel Hamlin, Mayank Varia
In this work, we construct the first DORAM schemes in the 2-server, semi-honest setting that simultaneously achieve sublinear server computation and constant rounds of communication.
We provide two constant-round constructions, one based on square root ORAM that has $O(\sqrt{N}\log N)$ local computation and another based on secure computation of a doubly efficient PIR that achieves local computation of $O(N^\epsilon)$ for any $\epsilon > 0$ but that allows the servers to distinguish between reads and writes. As a building block in the latter construction, we provide secure computation protocols for evaluation and interpolation of multivariate polynomials based on the Fast Fourier Transform, which may be of independent interest.
Marco Holz, Benjamin Judkewitz, Helen Möllering, Benny Pinkas, Thomas Schneider
Howard M. Heys
Rachit Rawat, Mahabir Prasad Jhanwar
The existing SSO systems built on distributed token generation techniques, including the PASTA framework, do not admit password-update functionality. In this work, we address this issue by proposing a password-update functionality into the PASTA framework. We call the modified framework PAS-TA-U.
As a concrete application, we instantiate PAS-TA-U to implement in Python a distributed SSH key manager for enterprise networks (ESKM) that also admits a password-update functionality for its clients. Our experiments show that the overhead of protecting secrets and credentials against breaches in our system compared to a traditional single server setup is low (average 119 ms in a 10-out-of-10 server setting on Internet with 80 ms round trip latency).
Deepraj Pandey, Nandini Agrawal, Mahabir Prasad Jhanwar
We present CovidBloc, a contact tracing system that implements the COVID 19 exposure database on Hyperledger Fabric Blockchain Network. Like most decentralized contact tracing application, the participants of the CovidBloc are: (1) a mobile application running on a bluetooth-equipped smartphone, (2) a web dashboard for health officials, and (3) a backend server acting as a repository for data being collected. We have implemented all components of CovidBloc to make it a fully functional contact tracing application. It is hosted at https://anonymous.4open.science/r/c6caad6d-62a4-463c-8301-472e421b931f/.
The mobile application for CovidBloc is developed for Android. The exposure notification system in our mobile application is implemented as per the recently released draft documentation by Google and Apple. The exposure notification API from Google and Apple is only available to a limited number of teams per country.
The backend server is an important component of any automated contact tracing system which acts as a repository for exposure data to be pushed by smartphones upon authorization by the health staff. Since adding or removing information on the server has privacy consequences, it is required that the server should not be trusted. The backend server for CovidBloc is implemented on Hyperledger Fabric Blockchain network.
Anubhab Baksi, Shivam Bhasin, Jakub Breier, Anupam Chattopadhyay, Vinay B. Y. Kumar
As cryptography is one of the cornerstones of secure communication among devices, the pertinence of fault attacks is becoming increasingly apparent in a setting where a device can be easily accessed in a physical manner. In particular, two recently proposed fault attacks, Statistical Ineffective Fault Attack (SIFA) and the Fault Template Attack (FTA) are shown to be formidable due to their capability to bypass the common duplication based countermeasures. Duplication based countermeasures, deployed to counter the Differential Fault Attack (DFA), work by duplicating the execution of the cipher followed by a comparison to sense the presence of any effective fault, followed by an appropriate recovery procedure. While a handful of countermeasures are proposed against SIFA, no such countermeasure is known to thwart FTA to date.
In this work, we propose a novel countermeasure based on duplication, which can protect against both SIFA and FTA. The proposal is also lightweight with only a marginally additional cost over simple duplication based countermeasures. Our countermeasure further protects against all known variants of DFA, including Selmke, Heyszl, Sigls attack from FDTC 2016. It does not inherently leak side-channel information and is easily adaptable for any symmetric key primitive. The validation of our countermeasure has been done through gate-level fault simulation.