International Association
for Cryptologic Research

The increasing penetration of Online Social Networks (OSNs) prompts the need for effectively accessing and utilizing social networking information. In numerous applications, users need to make trust and/or access control decisions involving other (possibly stranger) users, and one important factor is often the existence of common social relationships. This motivates the need for secure and privacy-preserving techniques allowing users to assess whether or not they have mutual friends.

This paper introduces the Common Friends service, a framework for finding common friends which protects privacy of non-mutual friends and guarantees authenticity of friendships. First, we present a generic construction that reduces to secure computation of set intersection, while ensuring authenticity of announced friends via bearer capabilities. Then, we propose an efficient instantiation, based on Bloom filters, that only incurs a constant number of public-key operations and appreciably low communication overhead. Our software is designed so that developers can easily integrate Common Friends into their applications, e.g., to enforce access control based on users\' social proximity in a privacy-preserving manner. Finally, we showcase our techniques in the context of an existing application for sharing (tethered) Internet access, whereby users decide to share access depending on the existence of common friends. A comprehensive experimental evaluation attests to the practicality of proposed techniques.

We present a password-authenticated group key exchange protocol where each user has his/her own password. Advantage of such protocol is in short passwords, which can be easily memorized. On the other hand these protocols face the low password entropy. In the first part we define security model based on models of Abdalla, Fouque and Pointcheval and Bellare, Pointcheval, Rogaway. We construct MLHL (Multi-LHL) protocol, which is based on LHL protocol proposed by Lee, Hwang and Lee. However, LHL protocol is flawed as pointed by Abdalla, Bresson, Chevassut and Choo, Raymond. We prove that our protocol is secure authenticated key exchange protocol with forward secrecy property and that the protocol is resistant against attacks on LHL protocol.

Proof-of-retrievability schemes have been a topic of considerable recent interest. In these schemes, a client gives a file M to a server with the understanding that the server will securely store M. A suitable challenge-response protocol is invoked by the client in order for the client to gain confidence that M is indeed being correctly stored by the server. The definition of proof-of-retrievability schemes is based on the notion of an extractor that can recover the file once the challenge-response protocol is executed a sufficient number of times.

In this paper, we propose a new type of scheme that we term a proof-of-data-observability scheme. Our definition tries to capture the stronger requirement that the server must have

an actual copy of M in its memory space while it executes the challenge-response protocol.

We give some examples of schemes that satisfy this new security definition. As well, we analyze the efficiency and security of the protocols we present, and we prove some necessary conditions for the existence of these kinds of protocols.

One of the most challenging aspects in computer-supported voting is to combine the apparently conflicting requirements of privacy and verifiability. On the one hand, privacy requires that a vote cannot be traced back from the result to a voter, while on the other hand,

verifiability states that a voter can trace the effect of her vote on the result. This can be addressed using various privacy-enabling cryptographic primitives which also offer verifiability.

As more and more refined voting systems were proposed, understanding of first privacy and later verifiability in voting increased, and notions of privacy as well as notions of verifiability in voting became increasingly more refined. This has culminated in a variety of verifiable systems that use cryptographic primitives to ensure specific kinds of privacy. However, the corresponding privacy and verifiability claims are not often verified independently. When they are investigated, claims have been invalidated sufficiently often to warrant a cautious approach to them.

The multitude of notions, primitives and proposed solutions that claim to achieve both privacy and verifiability form an interesting but complex landscape. The purpose of this paper is to

survey this landscape by providing an overview of the methods, developments and current trends regarding privacy and verifiability in voting systems.

A fully homomorphic encryption (FHE) scheme is envisioned as being a key cryptographic tool in building a secure and reliable cloud computing environment, as it allows arbitrarily evaluation of a ciphertext without revealing the plaintext. However, existing FHE implementations remain impractical due to their very high time and resource costs. Of the proposed schemes that can perform FHE to date, a scheme known as FHE over the integers has the ad-vantage of comparatively simpler theory, as well as the employment of a much shorter public key making its implementation somewhat more practical than other competing schemes.

To the author\'s knowledge, this paper presents the first hardware implemen-tations of encryption primitives for FHE over the integers using FPGA technol-ogy. First of all, a super-size hardware multiplier architecture utilising the Inte-ger-FFT multiplication algorithm is proposed, and a super-size hardware Barrett modular reduction module is designed incorporating the proposed multiplier. Next, two encryption primitives that are used in two schemes of FHE over the integers are designed employing the proposed super-size multiplier and modular reduction modules. Finally, the proposed designs are implemented and verified on the Xilinx Virtex-7 FPGA platform. Experimental results show that the speed improvement factors of up to 44.72 and 54.42 are available for the two FHE encryption schemes implemented in FPGA when compared to the corresponding software implementations. Meanwhile, the performance analysis shows that further improvement is speed of these FHE encryption primitives may still be possible.

We’re planning to make a hire at Security Innovation to support our NTRU crypto research program, including providing support for the codebase of our NTRU implementations once we make it available under GPL.

Responsibilities will include:

· Work on NTRU crypto research, including efficient signature schemes

· Helping to better understand lattice reduction algorithms, potentially including:

o A complete or partial reimplementation of algorithms developed by Nguyen and Chen to properly understand their claims

o Research into use of the structure of NTRU / ideal lattices to obtain improvements over generic lattice reduction algorithms

o Exploring the relationship between expected-shortest and actual-shortest vector in a lattice and how it affects reduction times

· Support cryptographic queries that come in to NTRU as a result of the GPL move, including participating in discussions on forums such as crypto.stackexchange and others

· Support the codebase of the GPL implementation of NTRU, including:

o General optimizations for the C implementation on 32- and 64-bit processors such as including multiple coefficients in a single word

o Architecture-specific optimizations such as exploring what advantage can be taken of SIMD, etc

o Potentially writing and/or managing a Java implementation

· Support standardization activity

o In particular, manage the passing of one or more NTRU-related TLS ciphersuite drafts through IETF.

Associate Professor - Mathematical Science

Full-time, Continuing (i.e., permanent) position

Annual Salary: $121,048 to $133,357 + 17% superannuation

Information Security forms one of the research strengths of the School. The Master of Applied Science in Information Security and Assurance is one of the programs in the school with more than 50 coursework students.

Please see the following link for further information about the research group

http://www.rmit.edu.au/browse;ID=3kk0nfsjwuuc

and the following for further information about Master\\\'s program in Information Security and Assurance

http://www.rmit.edu.au/programs/mc159

Situated within the College of Science, Engineering and Health, the School of Mathematical and Geospatial Sciences draws together disciplines involving the collection of data, the analysis of data, data security, and the understanding and optimisation of systems through modelling and visualisation. The School has more than 60 academic staff and over 70 postgraduate research students.

Reporting to the Head of School, the Associate Professor - Mathematical Science will be expected to be an active researcher. This will include supervising research students; undertaking and publishing high quality research, and applying for research grants.

Naturally occurring and maliciously injected faults reduce the reliability of cryptographic hardware and may leak confidential information. We develop a concurrent error detection (CED) technique called Recomputing with Permuted Operands (REPO). We show that it is cost effective in Advanced Encryption Standard (AES) and a secure hash

function Grøstl. We provide experimental results and formal proofs to show that REPO detects all single-bit and single-byte faults. Experimental results show that REPO achieves close to 100% fault coverage for multiple byte faults. The hardware and throughput overheads are compared with those of previously reported CED techinques on two Xilinx Virtex FPGAs. The hardware overhead is 12.4-27.3%, and the throughput is 1.2-23Gbps, depending on the AES architecture, FPGA family, and detection latency. The performance overhead ranges from 10% to 100% depending on the security

level. Moreover, the proposed technique can be integrated into various block cipher modes of operation. We also discuss the limitation of REPO and its potential vulnerabilities.

Submission: 10 January 2014
Notification: 14 March 2014
From June 10 to June 13
Location: Lausanne, Switzerland
More Information: http://acns2014.epfl.ch/

The notion of time plays an important role in many practically deployed cryptographic protocols, ranging from One-Time-Password (OTP) tokens to the Kerberos protocol. However, time is difficult to model in a Turing machine environment.

We propose the first such model, where time is modelled as a global counter T . We argue that this model closely matches several implementations of time in computer environments. The usefulness of the model is shown by giving complexity-theoretic security proofs for OTP protocols, HMQV-like one-round AKE protocols, and a variant of the basic Kerberos building block.

In this paper, we present a new class of public key cryptosystems by modifying K(XII)SE(1)PKC[1], referred to as K(XIII)SE(1)PKC, and a particular class of K(XIII)SE(1)PKC, Kp(XIII)SE(1)PKC. We show that K(XIII)SE(1)PKC would improve both the coding rate and the security, compared with K(XII)SE(1)PKC. We also show that Kp(XIII)SE(1)PKC realizes the coding rate of exactly 1.0. In a sharp contrast with the conventional code based PKC (CB･PKC) that uses Goppa code, in K(XII)SE(1)PKC, K(XIII)SE(1)PKC and Kp(XIII)SE(1)PKC, we do not care for the security of the primitive polynominal that generates the Reed-Solomon code.

Timed-release encryption is a kind of encryption scheme that a

recipient can decrypt only after a specified amount of time T

(assuming that we have a moderately precise estimate of his computing

power). A revocable timed-release encryption is one where,

before the time T is over, the sender can \"give back\" the

timed-release encryption, provably loosing all access to the data. We

show that revocable timed-release encryption without trusted parties

is possible using quantum cryptography (while trivially impossible

classically).

Along the way, we develop two proof techniques in the quantum random

oracle model that we believe may have applications also for other

protocols.

Finally, we also develop another new primitive, unknown recipient

encryption, which allows us to send a message to an

unknown/unspecified recipient over an insecure network in such a way

that at most one recipient will get the message.

In this article we propose a new cryptanalysis method for double-branch hash functions that we apply on the standard RIPEMD-128, greatly improving over know results. Namely, we were able to build a very good differential path by placing one non-linear differential part in each computation branch of the RIPEMD-128 compression function, but not necessarily in the early steps. In order to handle the low differential probability induced by the non-linear part located in later steps, we propose a new method for using the freedom degrees, by attacking each branch separately and then merging them with free message blocks. Overall, we present the first collision attack on the full RIPEMD-128 compression function as well as the first distinguisher on the full RIPEMD-128 hash function. Experiments on reduced number of rounds were conducted, confirming our reasoning and complexity analysis. Our results show that 16 years old RIPEMD-128, one of the last unbroken primitives belonging to the MD-SHA family, might not be as secure as originally thought.

Template Attack is widely accepted to be one of the most powerful side-channel attacks, because it is assumed that one has full knowledge of targeted crypto devices and thus be well capable of characterizing the side-channel leakages. However, whether or not Template Attack exploits side-channel leakages to the fullest is still not clear. In this paper, we present a negative answer to this central question, by introducing a normalization process into original Template Attack. We present Normalized Template Attack, which has the normalization process. Furthermore, we prove that Normalized Template Attack is better that its original counterpart in terms of leakage exploitation rate. We evaluate the key-recovery efficiency of Normalized Template Attack and original Template Attack as well under identical scenarios, by performing attacks against both simulated and real power traces. Our experimental results show that our method is valid end effective. Remarkably enough, this normalization process is of extremely low computation cost. Therefore, we argue that the

normalization process should be integrated as a necessary part of profile attacks in order to better understand the practical threats of these attacks.

In this work, elliptic curve cryptography (ECC) is used to make an efficient implementation of a public-key cryptography algorithm on the ARM Cortex-M0+. The goal of this implementation is to make not only a fast, but also a very low-power software implementation. To aid in the elliptic curve parameter selection, the energy consumption of different instructions on the ARM Cortex-M0+ was measured and it was found that there is a variation of up to 22.5% between different instructions. The instruction set architecture (ISA) and energy measurements were used to make a simulation of both a binary curve and a prime curve implementation, and the former was found to have a slightly faster execution time with a lower power consumption. Binary curve arithmetic use instructions which requires less energy than prime curve arithmetic on the target platform. A new field multiplication algorithm is proposed, called Lopez-Dahab with fixed registers, which is an optimization of the Lopez-Dahab (LD) algorithm. The proposed algorithm has a performance improvement of 15\\% over the LD with rotating registers algorithm (which is the current fastest optimization of the LD algorithm). A software implementation that uses the proposed algorithm was made in C and assembly, and on average our implementation of a random point multiplication requires 34.16uJ, whereas our fixed point multiplication requires 20.63uJ. The energy consumption of our implementation beats all known software implementations on embedded platforms, of a point multiplication, on the same equivalent security level by a factor of 7.4.

Physically Unclonable Functions (PUFs) are emerging as hardware security primitives. They are mainly used to generate secret keys which are inherently unique for every manufactured sample of a chip. Ring Oscillator (RO) PUFs are among the most widely researched PUFs. In this work, we claim various RO PUF constructions to be vulnerable against manipulation of their public helper data. Partial/full key-recovery is a threat for the following constructions, in chronological order. (1) Temperature-aware cooperative RO PUFs, proposed at HOST 2009. (2) The sequential pairing algorithm, proposed at HOST 2010. (3) Group-based RO PUFs, proposed at DATE 2013. (4) Or more general, all entropy distiller constructions proposed at DAC 2013.

In this article, we investigate the use of limited-birthday distinguishers to the context of hash functions. We first provide a proper understanding of the limited-birthday problem and demonstrate its soundness by using a new security notion Differential Target Collision Resistance (dTCR) that is related to the classical Target Collision Resistance (TCR) notion. We then solve an open problem and close the existing security gap by proving that the best known generic attack proposed at FSE 2010 for the limited-birthday problem is indeed the best possible method.

Moreover, we show that almost all known collision attacks are in fact more than just a collision finding algorithm, since the difference mask for the message input is usually fixed. A direct and surprising corollary is that these collision attacks are interesting for cryptanalysis even when their complexity goes beyond the $2^{n/2}$ birthday bound and up to the $2^{n}$ preimage bound, and can be used to derive distinguishers using the limited-birthday problem. Interestingly, cryptanalysts can now search for collision attacks beyond the $2^{n/2}$ birthday bound.

Finally, we describe a generic algorithm that turns a semi-free-start collision attack on a compression function (even if its complexity is beyond the birthday bound) into a distinguisher on the whole hash function when its internal state is not too wide. To the best of our knowledge, this is the first result that exploits classical semi-free-start collisions on the compression function to exhibit a weakness on the whole hash function. As an application of our findings, we provide distinguishers on reduced or full version of several hash functions, such as RIPEMD-128, SHA-256, Whirlpool, etc.

Ring signatures allow a signer to anonymously sign a message on behalf of a set of arbitrarily chosen signers called a ``ring\'\'.

Blind signatures, on the other hand, allow a user to obtain a signature on a message while maintaining the privacy of the message.

Blind ring signatures combine properties of both primitives and hence provide a strong notion of anonymity where the privacy of both the identity of the signer and the message is preserved.

Blind ring signatures find applications in various systems; including multi-authority e-voting and distributed e-cash systems.

In this paper we provide the first provably secure blind ring signature construction that does not rely on random oracles, which solves an open problem raised by Herranz and Laguillaumie at ISC 2006. We present different instantiations all of which are round-optimal (i.e.\\ have a two-move signing protocol), yield sub-linear size signatures, and meet strong security requirements.

In order to realize our constructions efficiently, we construct a sub-linear size set membership proof which works in the different bilinear group settings, which may be of independent interest.

As a secondary contribution, we show how to generically combine our set membership proof with any secure signature scheme meeting some conditions to obtain ring signatures whose security does not rely on random oracles. All our constructions work over the efficient prime-order bilinear group setting and yield signatures of sub-linear size. In addition, our constructions meet strong security requirements: namely, anonymity holds under full key exposure and unforgeability holds against insider-corruption.

Finally, we provide some example instantiations of the generic construction.

Naturally occurring and maliciously injected faults reduce the reliability of Advanced Encryption Standard (AES) and may leak confidential information. We developed an invariance-based concurrent error detection (CED) scheme which is independent of the implementation of AES encryption/decryption. Additionally, we improve the security of our scheme with Randomized CED Round Insertion and adaptive checking. Experimental results show that the invariance-based CED scheme detects all single-bit, all single-byte fault, and 99.99999997% of burst faults. The area and delay overheads of this scheme are compared with those of previously reported CED schemes on two Xilinx Virtex FPGAs. The hardware overhead is in the 13.2-27.3% range and the throughput is between 1.8-42.2Gbps depending on the AES architecture, FPGA family, and the detection latency. One can im-

plement our scheme in many ways; designers can trade off performance, reliability, and security according to the available resources.

The Department of Electrical and Electronic Engineering at Ariel University (Israel) invites applications for a tenure-track Lecturer or Senior Lecturer (Assistant Professor) post to begin in 2014. Positions are full-time, tenure-track, with eligible benefits. The candidate will lead a new Cyber Security Program in association with the Center for Homeland Security at Ariel University.