International Association
for Cryptologic Research

The existence of some structure in a code can lead to the decrease of security of the whole system built on it. Often subcodes are used to ``disguise'' the code as a ``general-looking'' one. However, the security of subcodes, whose Hadamard square is equal to the square of the base code, is reduced to the security of this code, i.e. this condition is undesirable. The paper finds the limiting conditions on the number of vectors of degree $ r $ removing of which retains this weakness for Reed--Muller subcodes and, accordingly, conditions for it to vanish. For $ r = 2 $ the exact structure of all resistant subcodes was found. For an arbitrary code $ RM(r, m) $, the desired number was estimated from both sides. Finally, the ratio of subcodes, whose Hadamard square is not equal to the square of the original code, was proven to tend to zero if additional conditions on the codimension of the subcode and the parameter $ r $ are imposed and $ m \rightarrow \infty $. Thus, the implementation of checks proposed in the paper helps to immediately filter out some insecure subcodes.

Cryptographic implementations deployed in real world devices often aim at (provable) security against the powerful class of side-channel attacks while keeping reasonable performances. Last year at Asiacrypt, a new formal verification tool named tightPROVE was put forward to exactly determine whether a masked implementation is secure in the well-deployed probing security model for any given security order t. Also recently, a compiler named Usuba was proposed to automatically generate bitsliced implementations of cryptographic primitives. This paper goes one step further in the security and performances achievements with a new automatic tool named Tornado. In a nutshell, from the high-level description of a cryptographic primitive, Tornado produces a functionally equivalent bitsliced masked implementation at any desired order proven secure in the probing model, but additionally in the so-called register probing model which much better fits the reality of software implementations. This framework is obtained by the integration of Usuba with tightPROVE+, which extends tightPROVE with the ability to verify the security of implementations in the register probing model and to fix them with inserting refresh gadgets at carefully chosen locations accordingly. We demonstrate Tornado on the lightweight cryptographic primitives selected to the second round of the NIST competition and which somehow claimed to be masking friendly. It advantageously displays performances of the resulting masked implementations for several masking orders and proves their security in the register probing model.

EUROCRYPT 2020 is the 39th Annual International Conference on the Theory and Applications of Cryptographic Techniques and one of the three general conferences of the International Association for Cryptologic Research (IACR).

Due to the current novel coronavirus outbreak, EUROCRYPT 2020 has been converted into an all-digital event, which will be taking place online during 11-15 May 2020.

Registration. The registration site (https://eurocrypt.iacr.org/2020/registration.php) for EUROCRYPT 2020 virtual attendance is now open. There will be no cost for virtual attendance itself but you have to register. If you have not already paid your IACR membership fee (USD 50 for regular members or USD 25 for student members) by attending a previous IACR event in 2020, you will need to pay that fee as part of registering for EUROCRYPT 2020.

Program. The program for EUROCRYPT 2020 is already available online (https://eurocrypt.iacr.org/2020/program.php). Sessions will be conducted as panel discussions in which authors give a very brief overview (5 minutes) of their papers, and then take live questions from the panel moderators and audience. There will also be links to papers and videos of longer talks by authors on their papers.

More details about virtual participation can be found here: https://eurocrypt.iacr.org/2020/participation.php

Event date: 20 June to 21 June 2020
Submission deadline: 28 May 2020

Event date: 5 May 2020

Status is building a communications tool with extreme security, coercion resistance and privacy in mind. As a protocol engineer in the Vac team, you will help us research and develop new and existing technologies in secure messaging.

Closing date for applications:

Contact: Ceri Power CA29 FB53 97E3 0232 106A  2DE6 9F07 1B10 A0D1 12EB

More information: https://grnh.se/c967211f1us

One funded PhD position (International/EU/UK) in hardware security with attractive travel grant for attending conferences.

Closing date: 8th May

We expect the PhD candidate to have a strong background in programming, digital circuit design, hardware/software implementation of algorithms, etc.

For more information on 'Why PhD with us?' see my website. https://www.cs.bham.ac.uk/~sinharos/

The PhD will be working with Dr. Sujoy Sinha Roy and will be based at the Security and Privacy group of the University of Birmingham's School of Computer Science. The National Cyber Security Centre (NCSC) and the Engineering and Physical Sciences Research Council (EPSRC) jointly recognise the research group as an Academic Centre of Excellence in Cyber Security Research (ACE-CSR).

If you are interested in the PhD position, please contact Dr. Sujoy Sinha Roy with a CV. For more information, please visit https://www.cs.bham.ac.uk/~sinharos/

Closing date for applications:

Contact: Dr. Sujoy Sinha Roy

BED: BOTNET ECONOMIC DISRUPTION VIA DARK WEB MARKETPLACE INFILTRATION Every year, cyber-attacks result in costs of hundreds of billions of dollars worldwide. One of the core facilitators of attacks are botnets, which are networks of infected computing devices. This PhD project will investigate a novel interdisciplinary approach for defending against botnets. BED will utilize research from the fields of network security, business economics and law, along with specialized research in botnet monitoring. The goal of BED is to: -identify and infiltrate botnet marketplaces with an emphasis on the dark web, -model the business economy of botnets, -Analyze the influence of botnet-specific parameters to the economy model -propose a botnet economy disruption plan. The PhD candidate will join the growing AAU cyber-security network in Copenhagen and work together with an interdisciplinary group of experts. The candidate will be able to collaborate with leading security experts worldwide and present their findings in top conferences all over the world. Supervisors: Jens Myrup Pedersen, Emmanouil Vasilomanolakis and Morten Falch Workplace: Campus Copenhagen

Closing date for applications:

Contact: Emmanouil Vasilomanolakis

More information: https://www.stillinger.aau.dk/vis-stilling/?vacancy=1098638

The Department of Computer Science at the University of Surrey is looking for a new permanent faculty member at lecturer level. I would appreciate your assistance in bringing this to the attention of outstanding candidates who may be interested in moving to Surrey.

We seek to appoint a lecturer in one or more of the following areas: machine learning, cloud computing, programming-languages principles, and the intersection of security and AI, which are already areas of research within the Department. We are also interested in candidates who have experience in data science, edge networks, social computing and DevOps security, in order to expand our research in new directions.

The Department is renowned for its security and artificial intelligence research, with publications in leading venues in artificial intelligence (TNNLS, TEVC, CBY, TSP, Machine Learning, Neural Computation, Bioinformatics, IJCAI, AAMAS), programming languages (FASE, PODC), security (CCS, S&P, Esorics, Euro S&P, CSF, TDSC, TIFS ), cryptography (Crypto, Eurocrypt), cloud computing and networking (InfoCOM, Trans. Networking), and web & social computing (WWW, ICWSM, and Web Science)

Notably,

we are active within professional organisations, working groups and technical committees of several standardisation bodies, such the IEEE Computational Intelligence Society, ISO, IETF, LoRa Alliance, IEEE Standards WG, ETSI, W3C, and leading the IET WG on e-voting

we host major international conferences such as ESORICS, ACNS, WCCI and GECCO,

we are leading European collaborative research on TPMs

our research on Bio-inspired Swarm Robotics research has been reported by the BBC https://www.bbc.co.uk/programmes/p022brpj and TechXplore https://techxplore.com/news/2020-04-bio-inspired-algorithms-collaborative-behaviors-robot.html

we have worked with the UK Parliament on understanding digital citizen engagement

we have developed methodologies for Enabling Serverless Deployment of Large-Scale AI Workloads

We encourage ambitious post-docs and early career lecturers to apply.

Closing date for applications:

Contact: Professor Helen Treharne, Head of Department, (h.treharne@surrey.ac.uk)

More information: https://jobs.surrey.ac.uk/vacancy.aspx?ref=020820

Contact tracing is one of the most important interventions to mitigate the spread of COVID-19/SARS-CoV-2. Smartphone-facilitated digital contact tracing may help to increase tracing capabilities as well as extend the coverage to those contacts one does not know in person. The emerging consensus is that a decentralized approach with local Bluetooth Low Energy (BLE) communication to detect contagion-relevant proximity, together with cryptographic protections, is necessary to guarantee the privacy of the users of such a system.

However, current decentralized protocols, including DP3T and the protocol by Canetti, Trachtenberg and Varia, do not sufficiently protect infected users from having their status revealed to their contacts, which may raise fear of stigmatization.

By taking a dual approach, we propose a new and practical solution with stronger privacy guarantees even against active adversaries. In particular, we solve the aforementioned problem with additional pseudorandom warning identities that are associated to the broadcasted public identity, but this association is only known to a non-colluding dedicated server, which does not learn to whom the public identity belongs. Then, only these anonymous warning identities are published.

Moreover, our solution allows warned contacts to prove that they have been in contact with infected users, an important feature in times of restricted testing capacities. Among other additional security measures, we detail how the use of secret sharing can prevent the unnecessary and potentially panic-inducing warning of contacts that have only been around the infected person for a very brief time period.

Multiple protocols implementing exciting cryptographic functionalities using blockchains such as time-lock encryption, one-time programs and fair multi-party computation assume the existence of a cryptographic primitive called extractable witness encryption. Unfortunately, there are no known efficient constructions (or even constructions based on any well studied assumptions) of extractable witness encryption. In this work, we propose a protocol that uses a blockchain itself to provide a functionality that is effectively the same as extractable witness encryption. By making small adjustments to the blockchain code, it is possible to easily implement applications that rely on extractable witness encryption and existed only as theoretical designs until now. There is also potential for new applications. As a key building block, our protocol uses a new and highly efficient batched dynamic proactive secret sharing scheme which may be of independent interest. We provide a proof-of-concept implementation of the extractable witness encryption construction and the underlying dynamic proactive secret sharing protocol.

We propose a new encoding algorithm for the simultaneous differential multidimensional scalar point multiplication algorithm $d$-MUL. Previous encoding algorithms are known to have major drawbacks in their efficient and secure implementation. Some of these drawbacks have been avoided in a recent paper in 2018 at a cost of losing the general functionality of the point multiplication algorithm. In this paper, we address these issues. Our new encoding algorithm takes the binary representations of scalars as input, and constructs a compact binary sequence and a permutation, which explicitly determines a regular sequence of group operations to be performed in $d$-MUL. Our algorithm simply slides windows of size two over the scalars and it is very efficient. As a result, while preserving the full generality of $d$-MUL, we successfully eliminate the recursive integer matrix computations in the originally proposed encoding algorithms. We also expect that our new encoding algorithm will make it easier to implement $d$-MUL in constant time. Our results can be seen as the efficient and full generalization of the one dimensional Montgomery ladder to arbitrary dimension.

The emergence of e-commerce has changed the way people trade. However, merchants are charged high fees for their use of the platform and for payment services. These costs are passed on to customers in the form of higher prices. Blockchain technology can provide lower transaction fees with high security and privacy level but is incapable of delivering the number of transactions per second demanded by real e-commerce. Establishing a layer above the blockchain to manage transactions which we called Blockchain Layer2 technology, has the potential to solve these issues. In this article, we focus on the effect that layer2 technology can provide in reducing fee costs and improving transaction volumes. We introduce the problems that the e-commerce industry is facing currently and how blockchain layer2 technology can help to address these issues. We list and describe the main layer2 mechanisms based on the Bitcoin and Ethereum blockchains. We discuss issues that arise when applying layer 2 technology to e-commerce. We analyse the costs associated with difference e-commerce payment network topologies and investigate the funds-capacity needed to support high levels of value transfer.

ECDSA is a widely adopted digital signature standard. A number of threshold protocols for ECDSA have been developed that let a set of parties jointly generate the secret signing key and compute signatures, without ever revealing the signing key. Threshold protocols for ECDSA have seen recent interest, in particular due to the need for additional security in cryptocurrency wallets where leakage of the signing key is equivalent to an immediate loss of money.

We propose a threshold ECDSA protocol secure against an active adversary in the honest majority model with abort. Our protocol is efficient in terms of both computation and bandwidth usage, and it allows the parties to pre-process parts of the signature, such that once the message to sign becomes known, they can compute a secret sharing of the signature very efficiently, using only local operations. We also show how to obtain fairness in the online phase at the cost of some additional work in the pre-processing, i.e., such that the protocol either aborts during the pre-processing phase, in which case nothing is revealed, or the signature is guaranteed to be delivered to all honest parties.

When designing a classical substitution-permutation network (SPN) permutation, every non-trivial choice of the S-box and of the affine layer provides security after a finite number of rounds. However, this is not necessarily the case for partial SPN (P-SPN) ciphers: Since the nonlinear part does not cover the full state, there may exist highly non-trivial choices of linear layers which, for example, do not provide security against statistical attacks.

Quite surprisingly, this direction has hardly been considered in the literature. For example, LowMC uses different linear layers in each round in order to avoid the problem, but this solution is quite expensive, both computationally and memory-wise. Zorro, another construction with an incomplete nonlinear layer, simply reuses the AES matrix, but this introduces weaknesses.

Working from an attacker's perspective and focusing on P-SPN ciphers, in this paper we present conditions which allow to set up attacks based on infinitely long invariant subspace trails -- even when using highly non-trivial linear layers. We also analyze the case in which the trail is not invariant, yet still an infinite number of rounds can be covered. In this paper, we consider two scenarios, namely active and inactive S-boxes. For the first case, we also provide a tool which is able to determine whether a given linear layer matrix is vulnerable against attacks based on our observations.

Finally, we point out that besides P-SPN ciphers, our results may also have a crucial impact on the HADES design strategy recently presented at Eurocrypt 2020, which mixes rounds with full S-box layers and rounds with partial S-box layers in order to guarantee security and achieve good performance in the target applications.

Recursive proof composition has been shown to lead to powerful primitives such as incrementally-verifiable computation (IVC) and proof-carrying data (PCD). All existing approaches to recursive composition take a succinct non-interactive argument of knowledge (SNARK) and use it to prove a statement about its own verifier. This technique requires that the verifier run in time sublinear in the size of the statement it is checking, a strong requirement that restricts the class of SNARKs from which PCD can be built. This in turn restricts the efficiency and security properties of the resulting scheme.

Bowe, Grigg, and Hopwood (ePrint 2019/1021) outlined how a modified recursive composition may be applied to a particular SNARK construction which does not have a sublinear-time verifier. However, they omit details about this method and do not prove that it satisfies any security property. Nonetheless, schemes based on this idea have already been implemented in software.

In this work we present a collection of results that establish the theoretical foundations for a significant generalization of the above approach. We define an accumulation scheme for a non-interactive argument, and show that this suffices to construct PCD, even if the argument itself does not have a sublinear-time verifier. Moreover we give constructions of accumulation schemes for SNARKs, which yield PCD schemes with novel efficiency and security features.

The surge of interest in decentralization-enabling technologies sparked by the recent success of Bitcoin and other blockchains has led to several new challenges in cryptography and protocol design. One such challenge concerns the widely used digital signature scheme -- ECDSA -- that has in particular been chosen to secure transactions in Bitcoin and several other blockchain systems. To empower decentralized interoperability between such blockchains one would like to implement distributed custody over Bitcoin accounts, which technically can be realized via a threshold ECDSA protocol. Even though several threshold ECDSA protocols already exist, as we argue, due to lack of robustness in signature generation, they are not well suited for deployment scenarios with large committees of parties, out of which a significant fraction might be malicious or prone to DDoS attacks. We propose a new threshold ECDSA protocol that improves upon the state-of-the-art solutions by enabling robustness and fault attributability during signature generation. In addition to that, we improve the signing time and bandwidth of previous solutions by moving expensive operations that are oblivious to the signed message to a separate setup phase.

Collusion-free (CF) and collusion-preserving (CP) protocols offer alternatives to standard multi-party computation (MPC) in settings where subliminal communication is undesirable, e.g., in decentralizing mediators in mediated games. However, all existing solutions make too strong and uninstantiable assumptions on the setups, such as physical presence of the parties, access to physical envelopes and opaque ballot boxes, or extreme isolation, where the only means of communication is a star-topology network among the parties with a special resource, the mediator, at its center---and the mediator needs to be aware of the function to be computed. The above state of affairs remained a limitation of such protocols, which was even reinforced by impossibility results. Thus, for years, it has been unclear if and how the above setup assumptions could be relaxed towards more realistic application scenarios.

In this work we provide the first solution to collusion preserving computation which uses weaker and more common assumptions than the above, i.e., an authenticated broadcast functionality and access to honestly generated trusted hardware tokens. We prove that our protocol is collusion-preserving secure (in short, CP secure) as long as no parties abort. In the case of an aborting adversary our protocol loses CP security, but still achieves standard security---against monolithic adversaries---and additionally identifies a corrupted party.

Leveraging the above identifiability property, we augment our protocol with a collateral and compensation mechanism which ensures that it is not profitable to abort, thereby obtaining CP security against incentive driven adversaries. To define (and prove) this latter result, we combine the Rational Protocol Design (RPD) methodology by Garay et al. [FOCS 2013] with the CP framework of Alwen et al. [CRYPTO 2012] to derive a definition of security in the presence of incentive-driven local adversaries which can be of independent interest.

Similar to existing protocols in the CP/CF literature, our protocols preserve, as a fallback, the traditional security properties---i.e., security against monolithic adversaries---even when the setup (i.e., the hardware tokens) is compromised or corrupted.

ElGamal public key encryption scheme has been designed in the 80’s. It is one of the first partial homomorphic encryption and one of the first IND-CPA probabilistic public key encryption scheme. A linear version has been recently proposed by Boneh et al. In this paper, we present a linear encryption based on a generalized version of ElGamal encryption scheme. We prove that our scheme is IND-CPA secure under the linear assumption. We design a also generalized ElGamal scheme from the generalized linear. We also run an evaluation of performances of our scheme. We show that the decryption algorithm is faster than the existing versions.

Abstract: Rotation operator is frequently used in several stream ciphers, including HC-128, Rabbit, and Salsa20, the final candidates for eSTREAM. This is because ‘Rotation operator (ROT)’ is simple but has very good dispersibility. In this paper, we propose a ‘disperse rotation operator (DRT)’, which has the same structure as ROT but has better dispersibility. In addition, the use of DRT instead of ROT has shown that the quality of the output stream of all three stream ciphers is significantly improved. On the other hand, the use of DRT instead of ROT in HC-128 stream cipher prevents the expansion of differentiated attacks based on LSB.