International Association
for Cryptologic Research

We are looking for a bright post-doctoral researcher focusing in theoretical cryptography and more precisely verifiable delegation of computation to work on a collaborative project on cloud-assisted computing.

The position is fully funded for 2 years and it would be extended under conditions for 2 more.

The post-doc will be hired at the department of Computer Science and Engineering at Chalmers and will be working under the supervision of Prof. Katerina Mitrokotsa.

The preferred starting date is in April 2019.

To apply send an email with subject: post-doc in cryptography and the following documents:

- CV, research statement, list of publications and names of at least two referees

Closing date for applications: 5 January 2019

Contact: Katerina Mitrokotsa

Associate Professor,

Chalmers University of Technology

Department of Computer Science and Engineering,

Gothenburg, Sweden

More information: http://www.cse.chalmers.se/~aikmitr/

Applications are invited for a post-doctoral fellow (PDF) and a doctoral (PhD) student in one or more of these areas: cryptographic engineering or applied cryptography as they relate to blockchain technologies, cryptocurrencies and digital payments. The successful candidates will be working in Professor Anwar Hasan’s research group in the Department of Electrical and Computer Engineering at the University of Waterloo.

PDF applicants with a recent PhD in Computer/Electrical Engineering or Computer Science and publications at premium venues are encouraged to send their CVs and cover letters via email to ahasan at uwaterloo.ca.

PhD student applicants with mathematical maturity and research experience in cryptographic engineering or applied cryptography, who meet the admission requirements for the PhD program in Electrical and Computer Engineering at the University of Waterloo, are encouraged to apply online following this link https://uwaterloo.ca/electrical-computer-engineering/future-graduate-students/programs

Closing date for applications: 11 January 2019

The Canadian Institute for Cybersecurity (CIC) is a comprehensive multidisciplinary training, research and development, and entrepreneurial unit that draws on the expertise of researchers in the social sciences, business, computer science, engineering, law and science.

Position Description:

We are currently looking for PhD and Post-doc researchers to fill various roles within our cyber security research and projects.

Required skills and experience:

- A computer science degree (Master for PhD candidates, PhD for Post-doc candidates) with expertise in network and information security, networking, and other relevant research area. (completed by the start of appointment)

- Strong communication and writing skills.

- Ability to do independent research, as well as to work collaboratively with other team members.

Helpful skills and experience:

- Application development using Java and Python

- Technical abilities in systems design, coding, testing, debugging, and maintenance.

- Demonstrated experience with the design and implementation of large networked and security systems.

Applications will be considered until the available positions are filled. To apply please include your curriculum vitae and the following:

- Research experience (projects, publications, etc.)

- Two representative publications (post-doc candidates)

- Proof of language proficiency (international applicants)

- Contact information (email, address, phone) of three references

Closing date for applications: 30 April 2019

Contact:

Arash Habibi Lashkari, PhD

Assistant Professor and Research Coordinator

Canadian Institute for Cybersecurity (CIC)

University of New Brunswick (UNB)

Fredericton, NB, Canada

A.habibi.l (at) unb.ca

More information: http://www.unb.ca/cic

We are looking for a postdoctoral researcher to work on isogeny-based cryptography.

Previous work in this field would be a plus but is not required. Generally, a strong background in algorithmic number theory, cryptographic protocols, cryptanalysis and/or applied cryptography is sought.

The position is for up to 30 months.

Informal inquiries are welcome.

Closing date for applications: 3 January 2019

Contact: Christophe Petit christophe.f.petit (at) gmail.com

More information: https://atsv7.wcn.co.uk/search_engine/jobs.cgi?SID=amNvZGU9MTc2OTA5NiZ2dF90ZW1wbGF0ZT03Njcmb3duZXI9NTAzMjUyMSZvd25lcnR5c

A PhD position is available to work on isogeny-based cryptography.

The ideal candidate will have a master in Mathematics, Computer Science or Electrical Engineering. Previous knowledge in cryptography and/or number theory is a plus.

Informal inquiries welcome.

Closing date for applications: 14 January 2019

Contact: Christophe Petit christophe.f.petit (at) gmail.com

More information: https://www.birmingham.ac.uk/postgraduate/courses/findaphd.aspx

The program for Real World Crypto 2019 is now published at https://rwc.iacr.org/2019/program.html.

RWC 2019 will be held January 9-11 in San Jose, California, USA.

We prove beyond-birthday-bound security for the well-known types of generalized Feistel networks, including: (1) unbalanced Feistel networks, where the $n$-bit to $m$-bit round functions may have $n\ne m$; (2) alternating Feistel networks, where the round functions alternate between contracting and expanding; (3) type-1, type-2, and type-3 Feistel networks, where $n$-bit to $n$-bit round functions are used to encipher $kn$-bit strings for some $k\ge2$; and (4) numeric variants of any of the above, where one enciphers numbers in some given range rather than strings of some given size. Using a unified analytic framework we show that, in any of these settings, for any $\varepsilon>0$, with enough rounds, the subject scheme can tolerate CCA attacks of up to $q\sim N^{1-\varepsilon}$ adversarial queries, where $N$ is the size of the round functions' domain (the size of the larger domain for alternating Feistel). This is asymptotically optimal. Prior analyses for generalized Feistel networks established security to only $q\sim N^{0.5}$ adversarial queries.

In this paper we are proposing a new member in the SNOW family of stream ciphers, called SNOW-V. The motivation is to meet an industry demand of very high speed encryption in a virtualized environment, something that can be expected to be relevant in a future 5G mobile communication system. We are revising the SNOW 3G architecture to be competitive in such a pure software environment, making use of both existing acceleration instructions for the AES encryption round function as well as the ability of modern CPUs to handle large vectors of integers (e.g. the Advanced Vector Extensions AVX from Intel). We have kept the general design from SNOW 3G, in terms of linear feedback shift register (LFSR) and Finite State Machine (FSM), but both entities are updated to better align with vectorized implementations. The LFSR part is new and operates 8 times the speed of the FSM. We have furthermore increased the total state size by using 128-bit registers in the FSM, we use the full AES encryption round function in the FSM update, and, finally, the initialization phase includes a masking with key bits at its end. The result is an algorithm generally much faster than AES-256 and with expected security not worse than AES-256.

Braid groups are infinite non-abelian groups naturally arising from geometric braids that have been used in cryptography for the last two decades. In braid group cryptography public braids often contain secret braids as a factor and it is hoped that rewriting the product of braid words hides the individual factors. We provide experimental evidence that this is in general not the case and argue that under certain conditions parts of the Garside normal form of factors can be found in the Garside normal form of their product. This observation can be exploited to decompose products in braid groups of the form $ABC$ when only $B$ is known.

Our decomposition algorithm yields a universal forgery attack on WalnutDSA^TM, which is one of the 20 proposed signature schemes that are being considered by NIST for standardization of quantum-resistant public-key cryptographic algorithms. Our attack on WalnutDSA^TM can universally forge signatures within seconds for both the 128-bit and 256-bit security level, given one random message-signature pair. The attack worked on 99.8% and 100% of signatures for the 128-bit and 256-bit security levels in our experiments.

Furthermore, we show that the decomposition algorithm can be used to solve instances of the conjugacy search problem and decomposition search problem in braid groups. These problems are at the heart of other cryptographic schemes based on braid groups.

An attempt to derive signer-efficient digital signatures from aggregate signatures was made in a signature scheme referred to as Structure-free Compact Rapid Authentication (SCRA) (IEEE TIFS 2017). In this paper, we first mount a practical universal forgery attack against the NTRU instantiation of SCRA by observing only 8161 signatures. Second, we propose a new signature scheme (FAAS), which transforms any single-signer aggregate signature scheme into a signer-efficient scheme. We show two efficient instantiations of FAAS, namely, FAAS-NTRU and FAAS-RSA, both of which achieve high computational efficiency. Our experiments confirmed that FAAS schemes achieve up to 100x faster signature generation compared to their underlying schemes. Moreover, FAAS schemes eliminate some of the costly operations such as Gaussian sampling, rejection sampling, and exponentiation at the signature generation that are shown to be susceptible to side-channel attacks. This enables FAAS schemes to enhance the security and efficiency of their underlying schemes. Finally, we prove that FAAS schemes are secure (in random oracle model), and open-source both our attack and FAAS implementations for public testing purposes.

In a recent paper Faonio, Nielsen and Venturi (ICALP 2015) gave new constructions of leakage-resilient signature schemes. The signature schemes proposed remain unforgeable against an adversary leaking arbitrary information on the entire state of the signer, including the random coins of the signing algorithm. The main feature of their signature schemes is that they offer a graceful degradation of security in situations where standard existential unforgeability is impossible. The notion, put forward by Nielsen, Venturi, and Zottarel (PKC 2014), defines a slack parameter $\gamma$ which, roughly speaking, describes how gracefully the security degrades. Unfortunately, the standard-model signature scheme of Faonio,Nielsen and Venturi has a slack parameter that depends on the number of signatures queried by the adversary.

In this paper we show two new constructions in the standard model where the above limitation is avoided. Specifically, the first scheme achieves slack parameter $O(1/\lambda)$ where $\lambda$ is the security parameter and it is based on standard number theoretic assumptions, the second scheme achieves optimal slack parameter (i.e. $\gamma = 1$) and it is based on knowledge of the exponent assumptions. Our constructions are efficient and have leakage rate $1 - o(1)$, most notably our second construction has signature size of only 8 group elements which makes it the leakage-resilient signature scheme with the shortest signature size known to the best of our knowledge.

Proofs of liabilities are used for applications, function like banks or Bitcoin exchanges, to prove the sums of money in their dataset that they should owe. The Maxwell protocol, a cryptographic proof of liabilities scheme which relies on a data structure well known as the summation Merkle tree, utilizes a Merkle approach to prove liabilities in the decentralized setting, i.e., clients independently verify they are in the dataset with no trusted auditor. In this paper, we go into the Maxwell protocol and the summation Merkle tree. We formalize the Maxwell protocol and show it is not secure. We present an attack with which the proved liabilities using the Maxwell protocol are less than the actual value. This attack can have significant consequences: A Bitcoin exchange controlling a total of $n$ client accounts can present valid liabilities proofs including only one account balance in its dataset. We suggest two improvements to the Maxwell protocol and the summation Merkle tree, and present a formal proof for the improvement that is closest in spirit to the Maxwell protocol. Moreover, we show the DAM scheme, a micropayment scheme of Zerocash which adopts the Maxwell protocol as a tool to disincentivize double/multiple spending, is vulnerable to an multi-spending attack. We show the Provisions scheme, which adopts the Maxwell protocol to extend its privacy-preserving proof of liabilities scheme, is also infected by a similar attack.

In this work, we consider the natural goal of designing secret sharing schemes that ensure security against a powerful adaptive adversary who may learn some ``leaked'' information about all the shares. We say that a secret sharing scheme is $p$-party leakage-resilient, if the secret remains statistically hidden even after an adversary learns a bounded amount of leakage, where each bit of leakage can depend jointly on the shares of an adaptively chosen subset of $p$ parties. A lot of works have focused on designing secret sharing schemes that handle individual and (mostly) non-adaptive leakage for (some) threshold secret sharing schemes [DP07,DDV10,LL12,ADKO15,GK18,BDIR18].

We give an unconditional compiler that transforms any standard secret sharing scheme with arbitrary access structure into a $p$-party leakage-resilient one for $p$ logarithmic in the number of parties. This yields the first secret sharing schemes secure against adaptive and joint leakage for more than two parties.

As a natural extension, we initiate the study of leakage-resilient non-malleable secret sharing} and build such schemes for general access structures. We empower the computationally unbounded adversary to adaptively leak from the shares and then use the leakage to tamper with each of the shares arbitrarily and independently. Leveraging our $p$-party leakage-resilient schemes, we also construct such non-malleable secret sharing schemes: any such tampering either preserves the secret or completely `destroys' it. This improves upon the non-malleable secret sharing scheme of Goyal and Kumar (CRYPTO 2018) where no leakage was permitted. Leakage-resilient non-malleable codes can be seen as 2-out-of-2 schemes satisfying our guarantee and have already found several applications in cryptography [LL12,ADKO15,GKPRS18,GK18,CL18,OPVV18].

Our constructions rely on a clean connection we draw to communication complexity in the well-studied number-on-forehead (NOF) model and rely on functions that have strong communication-complexity lower bounds in the NOF model (in a black-box way). We get efficient $p$-party leakage-resilient schemes for $p$ upto $O(\log n)$ as our share sizes have exponential dependence on $p$. We observe that improving this dependence from $2^{O(p)}$ to $2^{o(p)}$ will lead to progress on longstanding open problems in complexity theory.

We construct a genus 2 curve inside the product of 2 elliptic curves. The formula for this construction has appeared in a previous paper. The current paper discusses how this formula arises naturally by using some theory of elliptic Kummer surfaces

Proxy re-encryption (PRE) enables delegation of decryption rights by entrusting a proxy server with special information, that allows it to transform a ciphertext under one public key into a ciphertext of the same message under a different public key. It is important to note that, the proxy which performs the re-encryption learns nothing about the message encrypted under either public keys. Due to its transformation property, proxy re-encryption schemes have practical applications in distributed storage, encrypted email forwarding, Digital Rights Management (DRM) and cloud storage. From its introduction, several proxy re-encryption schemes have been proposed in the literature, and a majority of them have been realized using bilinear pairing. In Africacrypt 2010, the first PKI-based collusion resistant CCA secure PRE scheme without pairing was proposed in the random oracle model. In this paper, we point out an important weakness in the scheme. We also present the first collusion-resistant pairing-free unidirectional proxy re-encryption scheme which meets CCA security under a variant of the computational Diffie-Hellman hardness assumption in the random oracle model.

Proof-of-Stake (PoS) protocols have been actively researched for the past few years. PoS finds direct applicability in permissionless blockchain platforms and emerges as one of the strongest candidates to replace the largely inefficient Proof of Work mechanism that is currently plugged in the majority of existing permissionless blockchain systems. Although a number of PoS variants have been proposed, these protocols suffer from a number of security shortcomings. Namely, most existing PoS variants are either subject to the nothing at stake, the long range, or the stake grinding attacks which considerably degrade security in the blockchain. These shortcomings do not result from a lack of foresight when designing these protocols, but are inherently due to the ease of manipulating "stake" when compared to other more established variants, such as "work". In this paper, we address these problems and propose a secure Proof of Stake protocol, PoTS, that leverages Trusted Execution Environments (TEEs), such as Intel SGX, to ensure that each miner can generate at most one block per "height" for strictly increasing heights—thus thwarting the problem of nothing at stake and a large class of long-range attacks. In combination with TEEs, PoTS additionally uses cryptographic techniques to also prevent grinding attacks and protect against posterior corruption. We show that our protocol is secure, in the sense of well-established cryptographic notions for blockchain protocols, down to realistic hardware assumptions on TEE and well-established cryptographic assumptions. Finally, we evaluate the performance of our proposal by means of implementation. Our evaluation results show that PoTS offers a strong tradeoff between security of performance of the underlying PoS protocol.

So far, the topic of merged mining has mainly been considered in a security context, covering issues such as mining power centralization or crosschain attack scenarios. In this work we show that key information for determining blockchain metrics such as the fork rate can be recovered through data extracted from merge mined cryptocurrencies. Specifically, we reconstruct a long-ranging view of forks and stale blocks in Bitcoin from its merge mined child chains, and compare our results to previous findings that were derived from live measurements. Thereby, we show that live monitoring alone is not sufficient to capture a large majority of these events, as we are able to identify a non-negligible portion of stale blocks that were previously unaccounted for. Their authenticity is ensured by cryptographic evidence regarding both, their position in the respective blockchain, as well as the Proof-of-Work difficulty.

Furthermore, by applying this new technique to Litecoin and its child cryptocur rencies, we are able to provide the first extensive view and lower bound on the stale block and fork rate in the Litecoin network. Finally, we outline that a recovery of other important metrics and blockchain characteristics through merged mining may also be possible.

This paper proposes two closely related asymmetric key (or a public key) schemes for key exchange whose security is based on the notion of ideal secrecy. In the first scheme, the private key consists of two singular matrices, a polar code matrix and a random permutation matrix all over the binary field. The sender transmits addition of two messages over a public channel using the public key of the receiver. The receiver can decrypt individual messages using the private key. An adversary, without the knowledge of the private key, can only compute multiple equiprobable solutions in a space of sufficiently large size related to the dimension of the kernel of the singular matrices. This achieves security in the sense of ideal secrecy. The next scheme extends over general matrices. The two schemes are cryptanalyzed against various attacks.

We present Ouroboros Crypsinous, the first privacy-preserving proof-of-stake (PoS) blockchain protocol. To model its security we give a thorough treatment of private ledgers in the universal composition (UC) setting that might be of independent interest. To prove our protocol secure against adaptive attacks, which are particularly critical in the PoS setting, we introduce a new coin evolution technique that relies on a SNARKs mechanism and key-private forward secure encryption. The latter primitive---and the associated construction---can be of independent interest. We stress that existing approaches to private blockchains, such as the proof-of-work-based Zerocash are analyzed only against static corruptions.

Cloud storage enables its users to store confidential information as encrypted files in the cloud. A cloud user (say Alice) can share her encrypted files with another user (say Bob) by availing proxy re-encryption services of the cloud. Proxy Re-Encryption (PRE) is a cryptographic primitive that allows transformation of ciphertexts from Alice to Bob via a semi-trusted proxy, who should not learn anything about the shared message. Typically, the re-encryption rights are enabled only for a bounded, fixed time and malicious parties may want to decrypt or learn messages encrypted for Alice, even beyond that time. The basic security notion of PRE assumes the proxy (cloud) is semi-trusted, which is seemingly insufficient in practical applications. The proxy may want to collude with Bob to obtain the private keys of Alice for later use. Such an attack is called collusion attack, allowing colluders to illegally access all encrypted information of Alice in the cloud. Hence, achieving collusion resistance is indispensable to real-world scenarios. Realizing collusion-resistant PRE has been an interesting problem in the ID-based setting. To this end, several attempts have been made to construct a collusion-resistant IB-PRE scheme and we discuss their properties and weaknesses in this paper. We also present a new collusion-resistant IB-PRE scheme that meets the adaptive CCA security under the decisional bilinear Diffie-Hellman hardness assumption and its variant in the random oracle model.