International Association
for Cryptologic Research

Non-malleable codes for the split-state model allow to encode a message into two parts, such that arbitrary independent tampering on each part, and subsequent decoding of the corresponding modified codeword, yields either the same as the original message, or a completely unrelated value. Continuously non-malleable codes further allow to tolerate an unbounded (polynomial) number of tampering attempts, until a decoding error happens. The drawback is that, after an error happens, the system must self-destruct and stop working, otherwise generic attacks become possible.

In this paper we propose a solution to this limitation, by leveraging a split-state refreshing procedure. Namely, whenever a decoding error happens, the two parts of an encoding can be locally refreshed (i.e.,\ without any interaction), which allows to avoid the self-destruct mechanism in some applications. Additionally, the refreshing procedure can be exploited in order to obtain security against continual leakage attacks. We give an abstract framework for building refreshable continuously non-malleable codes in the common reference string model, and provide a concrete instantiation based on the external Diffie-Hellman assumption.

Finally, we explore applications in which our notion turns out to be essential. The first application is a signature scheme tolerating an arbitrary polynomial number of split-state tampering attempts, without requiring a self-destruct capability, and in a model where refreshing of the memory happens only after an invalid output is produced. This circumvents an impossibility result from a recent work by Fuijisaki and Xagawa (Asiacrypt 2016). The second application is a compiler for tamper-resilient read-only RAM programs. In comparison to other tamper-resilient RAM compilers, ours has several advantages, among which the fact that, in some cases, it does not rely on the self-destruct feature.

In this paper, we propose a new type of non-recursive Mastrovito multiplier for $GF(2^m)$ using a $n$-term Karatsuba algorithm (KA), where $GF(2^m)$ is defined by an irreducible trinomial, $x^m+x^k+1, m=nk$. We show that such a type of trinomial combined with the $n$-term KA can fully exploit the spatial correlation of entries in related Mastrovito product matrices and lead to a low complexity architecture. The optimal parameter $n$ is further studied. As the main contribution of this study, the lower bound of the space complexity of our proposal is about $O(\frac{m^2}{2}+m^{3/2})$. Meanwhile, the time complexity matches the best Karatsuba multiplier known to date. To the best of our knowledge, it is the first time that Karatsuba-based multiplier has reached such a space complexity bound while maintaining relatively low time delay.

We analyze security properties of a two-party key-agreement protocol recently proposed by I. Anshel, D. Atkins, D. Goldfeld, and P. Gunnels, called Kayawood protocol. At the core of the protocol is an action (called E-multiplication) of a braid group on some finite set. The protocol assigns a secret element of a braid group to each party (private key). To disguise those elements, the protocol uses a so-called cloaking method that multiplies private keys on the left and on the right by specially designed elements (stabilizers for E-multiplication).

We present a heuristic algorithm that allows a passive eavesdropper to recover Alice's private key by removing cloaking elements. Our attack has 100% success rate on randomly generated instances of the protocol for the originally proposed parameter values and for recent proposals that suggest to insert many cloaking elements at random positions of the private key. Our implementation of the attack is available on GitHub.

We consider recent constructions of $1$-out-of-$N$ OT-extension from Kolesnikov and Kumaresan (CRYPTO 2013) and from Orrú et al. (CT-RSA 2017), based on binary error-correcting codes. We generalize their constructions such that $q$-ary codes can be used for any prime power $q$. This allows to reduce the number of base $1$-out-of-$2$ OT's that are needed to instantiate the construction for any value of $N$, at the cost of increasing the complexity of the remaining part of the protocol. We analyze these trade-offs in some concrete cases.

OpenStack is the prevalent open-source, non-proprietary package for managing cloud services and data centers. It is highly complex and consists of multiple inter-related components which are developed by separate, loosely coordinated groups. We initiate an effort to provide a rigorous and holistic security analysis of OpenStack. Our analysis has the following key features:

-It is user-centric: It stresses the security guarantees given to users of the system, in terms of privacy, correctness, and timeliness of the services.

-It provides defense in depth: It considers the security of OpenStack even when some of the components are compromised. This departs from the traditional design approach of OpenStack, which assumes that all services are fully trusted.

-It is modular: It formulates security properties for individual components and uses them to assert security properties of the overall system.

We base our modeling and security analysis in the universally composable (UC) security framework, which has been so far used mainly for analyzing security of cryptographic protocols. Indeed, demonstrating how the UC framework can be used to argue about security-sensitive systems which are mostly non-cryptographic in nature is another main contribution of this work.

Our analysis covers only a number of core components of OpenStack. Still, it uncovers some basic and important security trade-offs in the design. It also naturally paves the way to a more comprehensive analysis of OpenStack.

We study the problem of building a verifiable delay function (VDF). A VDF requires a specified number of sequential steps to evaluate, yet produces a unique output that can be efficiently and publicly verified. VDFs have many applications in decentralized systems, including public randomness beacons, leader election in consensus protocols, and proofs of replication. We formalize the requirements for VDFs and present new candidate constructions that are the first to achieve an exponential gap between evaluation and verification time.

In this paper we proposed an ultra-lightweight cipher GRANULE. It is based on Feistel network which encrypts 64 bits of data with 80/128 bits of key. GRANULE needs very less memory space as compared to existing lightweight ciphers .GRANULE needs 1288 GEs for 80 bit and 1577 GEs for 128 bit key size. It also shows good resistance against linear and differential cryptanalysis. GRANULE needs very small footprint area and provides robust secure design which thwart attacks like biclique attack, zero correlation attack, meet in the middle attack ,key schedule attack and key collision attack. GRANULE is having a strong S-box which is the key designing aspect in any cipher design. In this paper GRANULE is proposed with 32 rounds which are enough to provide resistance against all possible types of attacks. GRANULE consumes very less power as compared to other modern lightweight ciphers. We believe GRANULE cipher is the best suited cipher for providing robust security in applications like IoT.

Sensitive data is often outsourced to cloud servers, with the server performing computation on the data. Computational correctness must be efficiently verifiable by a third party while the input data remains confidential. This paper introduces CHQS, a homomorphic signature scheme from bilinear groups fulfilling these requirements. CHQS is the first such scheme to be both context hiding and publicly verifiable for arithmetic circuits of degree two. It also achieves amortized efficiency: after a precomputation, verification can be faster than the evaluation of the circuit itself.

The ransomware nightmare is taking over the internet impacting common users,small businesses and large ones. The interest and investment which are pushed into this market each month, tells us a few things about the evolution of both technical and social engineering and what to expect in the short-coming future from them. In this paper we analyze how ransomware programs developed in the last few years and how they were released in certain market segments throughout the deep web via RaaS, exploits or SPAM, while learning from their own mistakes to bring profit to the next level. We will also try to highlight some mistakes that were made, which allowed recovering the encrypted data, along with the ransomware authors preference for specific encryption types, how they got to distribute, the silent agreement between ransomwares, coin-miners and bot-nets and some edge cases of encryption, which may prove to be exploitable in the short-coming future.

This paper revisits the security conditions of masked hardware implementations. We describe a new, succinct, information-theoretic condition to ensure security in the presence of glitches. This single condition includes, but is not limited to, previous security notions such as those used in threshold implementations. As a consequence, we can prove the security of masked functions that work with non-uniform input sharings. Our notion naturally generalizes to higher orders. Furthermore, we can apply our condition in a tool that efficiently tests and validates the resistance of masked hardware circuits against DPA. Finally, we also treat the notion of (strong) non-interference from an information-theoretic point-of-view in order to unify the different security concepts and pave the way to the verification of composability in the presence of glitches.

Non-Malleable Codes (NMC) were introduced by Dziembowski, Pietrzak and Wichs in ICS 2010 as a relaxation of error correcting codes and error detecting codes. Faust, Mukherjee, Nielsen, and Venturi in TCC 2014 introduced an even stronger notion of non-malleable codes called continuous non-malleable codes where security is achieved against continuous tampering of a single codeword without re-encoding. We construct information theoretically secure CNMC resilient to bit permutations and overwrites, this is the first Continuous NMC constructed outside of the split-state model. In this work we also study relations between the CNMC and parallel CCA commitments. We show that the CNMC can be used to bootstrap a \sd\ parallel CCA bit commitment to a \sd\ parallel CCA string commitment, where \sd\ parallel CCA is a weak form of parallel CCA security. Then we can get rid of the \sd\ limitation obtaining a parallel CCA commitment, requiring only one-way functions.

Randomness testing of binary sequences generated by any keystream generator is of paramount importance to both designer and attacker. Here we consider a word-oriented keystream generator known as multiple-recursive matrix generator, which was introduced by Niederreiter (1993). Using NIST statistical test suite as well as DieHarder statistical package, we analyze randomness properties of binary sequences generated by multiple-recursive matrix generator and show that these sequences are not really adequate for any cryptographic applications. We also propose nonlinearly filtered multiple-recursive matrix generator based a special nonlinear function and establish that sequences generated by such a nonlinearly filtered multiple-recursive matrix generator provide good randomness results. Moreover, we compare our randomness test results with some of the recent lightweight stream ciphers like Lizard, Fruit, and Plantlet.

We initiate a study of the security of cryptographic primitives in the presence of efficient tampering attacks to the randomness of honest parties. More precisely, we consider p-tampering attackers that may \emph{efficiently} tamper with each bit of the honest parties' random tape with probability p, but have to do so in an ``online'' fashion. Our main result is a strong negative result: We show that any secure encryption scheme, bit commitment scheme, or zero-knowledge protocol can be ``broken'' with probability $p$ by a $p$-tampering attacker. The core of this result is a new Fourier analytic technique for biasing the output of bounded-value functions, which may be of independent interest.

We also show that this result cannot be extended to primitives such as signature schemes and identification protocols: assuming the existence of one-way functions, such primitives can be made resilient to (\nicefrac{1}{\poly(n)})-tampering attacks where $n$ is the security~parameter.

Weeve is a global network of IoT devices autonomously buying and selling device data. Powered by next-generation cryptography, cryptoeconomics, incentive mechanisms, and secured by the blockchain, Weeve is the basis for the Economy of Things – generating high-quality data stream networks. Weeve’s goal is to empower the commercialization of IoT through sharing data in a new era of data economies. We look for applicants with keen interest in at least one of the following topics:

Smart Contracting and Blockchain applications (e.g. Ethereum, Hyperledger, Cardano),

Blockchain-enabled mechanism design and applications (e.g. graded token-curated registries),

Radically new voting schemes beyond “the richer get richer” (e.g. quadratic voting, token-curated voting),

Scalable consensus protocols ,

Cryptographic algorithms (e.g. NIZKs, SNARGs, STARKs) & privacy-enhancing/GDPR-friendly protocols (e.g. MPC,)

System Security (e.g. ARM Trustzone, Intel SGX)

We solicit applications at various entry levels, from junior to senior, covering the complete spectrum from full-time research to development. We also appreciate and support research internships of PhDs and PostDocs. We offer a competitive salary, an academic environment, and access to Berlin’s vibrant blockchain ecosystem. Weeve leaves much freedom for pursuing one’s own ideas and supports this with condensing research ideas into a PhD and disseminating those to the blockchain community (meetups, conferences, etc.).

Closing date for applications: 31 July 2018

Contact: For technical inquiries, please contact Prof. Dr. Sebastian Gajek: (sebastian.gajek (at) weeve.network)

For recruitment queries, contact NBT Tech Recruiter: Ayca (ayca.kuzuimamlar (at) nbt.ag).

More information: https://weeve.network

The CRYPTO Research Group of LMV (Laboratoire de Mathématiques de Versailles), part of Versailles-St-Quentin-en-Yvelines University (UVSQ), invites applications for a postdoctoral researcher position in the area of Post-Quantum Cryptography.

The position is available immediately for one year, and is renewable, based on mutual interest and availability of funding. The starting date can be arranged as convenient.

The candidates are expected to:

- have completed their PhD degree in cryptography;

- have adequate cryptography research experience demonstrated through a strong publication record.

Applications should be sent via email and should include a CV, a list of publications, a short research proposal, and contact information for one or two persons who are willing to give references.

Closing date for applications: 30 June 2018

Contact: Contact: Prof. Louis Goubin, Louis.Goubin (at) uvsq.fr

More information: http://lmv.math.cnrs.fr/equipes/crypto/

SFN is a lightweight block cipher designed to be compact in hardware environment and also efficient in software platforms. Compared to the conventional block ciphers that are either Feistel or Substitution-Permutation (SP) network based, SFN has a different encryption method which uses both SP network structure and Feistel network structure to encrypt. SFN supports key lengths of 96 bits and its block length is 64 bits. In this paper, we propose an attack on full SFN by using the related key distinguisher. With this attack, we are able to recover the keys with a time complexity of 2^{60.58} encryptions. The data and memory complexity of the attacks are negligible. In addition, in the single key mode, we present a meet in the middle attack against the full rounds block cipher for which the time complexity is 2^{80} SFN calculations and the memory complexity is 2^{87} bytes. The date complexity of this attack is only a single known plaintext and its corresponding ciphertext.

In this paper we study the security of a proposal for Post-Quantum Cryptography from both a number theoretic and cryptographic perspective. Charles-Goren-Lauter in 2006 proposed two hash functions based on the hardness of finding paths in Ramanujan graphs. One is based on Lubotzky--Phillips--Sarnak (LPS) graphs and the other one is based on Supersingular Isogeny Graphs. A 2008 paper by Petit-Lauter-Quisquater breaks the hash function based on LPS graphs. On the Supersingular Isogeny Graphs proposal, recent work has continued to build cryptographic applications on the hardness of finding isogenies between supersingular elliptic curves. A 2011 paper by De Feo-Jao-Pl\^ut proposed a cryptographic system based on Supersingular Isogeny Diffie--Hellman as well as a set of five hard problems. In this paper we show that the security of the SIDH proposal relies on the hardness of the SIG path-finding problem introduced in [CGL06]. In addition, similarities between the number theoretic ingredients in the LPS and Pizer constructions suggest that the hardness of the path-finding problem in the two graphs may be linked. By viewing both graphs from a number theoretic perspective, we identify the similarities and differences between the Pizer and LPS graphs.

XS-circuits describe block ciphers that utilize 2 operations: X) bitwise modulo 2 addition of binary words and S) substitution of words using key-dependent S-boxes with possibly complicated internal structure. We propose a model of XS-circuits which, despite the simplicity, covers a rather wide range of block ciphers. In our model, several instances of a simple round circuit, which contains only one S~operation, are linked together and form a compound circuit called a cascade. S operations of a cascade are interpreted as independent round oracles. We deal with diffusion characteristics of cascades. These characteristics are related to the cryptographic strength of corresponding block ciphers. We obtain results on invertibility, transitivity and 2-transitivity of mappings induced by round circuits and their cascades. We provide estimates on the first and second activation times where the i-th activation time is the minimum number of rounds which guarantees that at least i round oracles get different queries while processing two different cascade's inputs. The activation times are related to differential cryptanalysis. We introduce the similarity and duality relations between round circuits. Cascades of related circuits have the same or dual diffusion characteristics. We find canonical representatives of classes of similar circuits and show that the duality between circuits is related to duality between differential and linear attacks against corresponding block ciphers. We discuss families of circuits with growing number of inputs. Such families can be used to build wide-block ciphers.

4-bit crypto S-boxes play a significant role in encryption and decryption of many cipher algorithms from last 4 decades. Generation and cryptanalysis of generated 4-bit crypto S-boxes is one of the major concerns of modern cryptography till now. In this paper 48, 4-bit crypto S-boxes are generated with addition of all possible additive constants to the each element of crypto S-box of corresponding multiplicative inverses of all elemental polynomials (EPs) under the concerned irreducible polynomials (IPs) over Galois field GF(2^4). Cryptanalysis of 48 generated 4-bit crypto S-boxes is done with all relevant cryptanalysis algorithms of 4-bit crypto S-boxes. The result shows the better security of generated 4-bit crypto S-boxes.

We propose a new computational problem over the noncommutative group, called the twin conjugacy search problem. This problem is related to the conjugacy search problem and can be used for almost all of the same cryptographic constructions that are based on the conjugacy search problem. However, our new problem is at least hard as the conjugacy search problem. Moreover, the twin conjugacy search problem have many applications. One of the most important applications, we propose a trapdoor test which can replace the function of the decision oracle. We also show other applications of the problem, including: a non-interactive key exchange protocol and a key exchange protocol, a new encryption scheme which is secure against chosen ciphertext attack, with a very simple and tight security proof and short ciphertexts, under a weak assumption, in the random oracle model.