International Association for Cryptologic Research

# IACR News Central

You can also access the full news archive.

Further sources to find out about changes are CryptoDB, ePrint RSS, ePrint Web, Event calender (iCal).

2015-06-05
00:17 [Pub][ePrint]

In this paper we analyze the security of the compression function of SHA-1 against collision attacks, or equivalently free-start collisions on the hash function. While a lot of work has been dedicated to the analysis of SHA-1 in the past decade, this is the first time that free-start collisions have been considered for this function.

We exploit the additional freedom provided by this model by using a new start-from-the-middle approach in combination with improvements on the cryptanalysis tools that have been developed for SHA-1 in the recent years. This results in particular in better differential paths than the ones used for hash function collisions so far.

Overall, our attack requires about $2^{50}$ evaluations of the compression function in order to compute a one-block free-start collision for a 76-step reduced version, which is so far the highest number of steps reached for a collision on the SHA-1 compression function. We have developed an efficient GPU framework for the highly branching code typical of a cryptanalytic collision attack and used it in an optimized implementation of our attack on recent GTX-970 GPUs.

We report that a single cheap US$350 GTX-970 is sufficient to find the collision in less than 5 days. This showcases how recent mainstream GPUs seem to be a good platform for expensive and even highly-branching cryptanalysis computations. Finally, our work should be taken as a reminder that cryptanalysis on SHA-1 continues to improve. This is yet another proof that the industry should quickly move away from using this function. 00:17 [Pub][ePrint] We give generic constructions of several fundamental cryptographic primitives based on a new encryption primitive that combines circular security for bit encryption with the so-called reproducibility property (Bellare et al. PKC 2003). At the heart of our constructions is a novel technique which gives a way of de-randomizing reproducible public-key bit-encryption schemes and also a way of reducing one-wayness conditions of a constructed trapdoor-function family (TDF) to circular security of the base scheme. The main primitives that we build from our encryption primitive include k-wise one-way TDFs (Rosen and Segev TCC 2009), CCA2-secure encryption and deterministic encryption. Our results demonstrate a new set of applications of circularly- secure encryption beyond fully-homomorphic encryption and symbolic soundness. Finally, we show the plausibility of our assumptions by showing that the DDH-based circularly-secure scheme of Boneh et al. (Crypto 2008) and the subgroup indistinguishability based scheme of Brakerski and Goldwasser are both reproducible. 00:17 [Pub][ePrint] \\textit{Khudra} is a block cipher proposed in the SPACE\'2014 conference, whose main design goal is to achieve suitability for the increasingly popular Field Programmable Gate Array (FPGA) implementation. It is an 18-round lightweight cipher based on recursive Feistel structure, with a 64-bit block size and 80-bit key size. In this paper, we compute the minimum number of active$F$-functions in differential characteristics in the related-key setting, and give a more accurate measurement of the resistance of \\textit{Khudra} against related-key differential cryptanalysis. We construct a related-key boomerang quartet with probability$2^{-48}$for the 14-round \\textit{Khudra}, which is better than the highest probability related-key boomerang quartet of the 14-round \\textit{Khudra} of probability at most$2^{-72}$claimed by the designers. Then we propose a related-key rectangle attack on the 16-round \\textit{Khudra} without whitening key by constructing a related-key rectangle distinguisher for 12-round \\textit{Khudra} with a probability of$2^{-23.82}$. The attack has time complexity of$2^{78.68}$memory accesses and data complexity of$2^{57.82}\$ chosen plaintexts, and requires only four related keys. This is the best known attack on the round-reduced \\textit{Khudra}.

2015-06-03
22:58 [Job][New]

Applications are invited for a PhD position in the field of cryptography at the Universitat Pompeu Fabra in Barcelona, Spain.

The applicant will join the research group in Wireless Communications and will be co-supervised by Dr. Vanesa Daza and Dr. Carla Ràfols. The topic of research will be interactions between multiparty computation and zero-knowledge proofs.

The candidate should have completed his/her master´s degree by Oct. 2015 in computer science, mathematics or a related area.

The starting date will be around Oct. 2015 and the student will receive a PhD stipend from the Universitat Pompeu Fabra (http://www.upf.edu/dtic_doctorate/_pdf/dtic_upf_phd_calll_2015_16.pdf)

Applications should start with a a short motivation letter, include a full CV, a copy of grade transcript(s) of completed studies and (when possible) one name of reference.

To apply or request further information, please send an email to

cryptoPhDapplications (at) upf.edu. The review of applications will start on June 15th and continue until the position is filled.

2015-06-02
20:30 [Event][New]

Submission: 17 December 2015
From April 13 to April 15
Location: Fes, Morocco

09:17 [Pub][ePrint]

Digital signature is a fundamental primitive with numerous applications. Following the development of pairing-based cryptography, several taking advantage of this setting have been proposed. Among them, the Camenisch-Lysyanskaya (CL) signature scheme is one of the most flexible and has been used as a building block for many other protocols. Unfortunately, this scheme suffers from a linear size in the number of messages to be signed which limits its use in many situations.

In this paper, we propose a new signature scheme with the same features as CL-signatures but without the linear-size drawback: our signature consists of only two elements, whatever the message length, and our algorithms are more efficient. This construction takes advantage of using type 3 pairings, that are already widely used for security and efficiency reasons.

We prove the security of our scheme without random oracles but in the generic group model. Finally, we show that protocols using CL-signatures can easily be instantiated with ours, leading to much more efficient constructions.

09:17 [Pub][ePrint]

We propose new generic key recovery attacks on Feistel-type block ciphers. The

proposed attack is based on the all subkeys recovery approach presented in SAC 2012, which

determines all subkeys instead of the master key. This enables us to construct a key recovery

attack without taking into account a key scheduling function. With our advanced techniques,

we apply several key recovery attacks to Feistel-type block ciphers. For instance, we show

8-, 9- and 11-round key recovery attacks on n-bit Feistel ciphers with 2n-bit key employing

random keyed F-functions, random F-functions, and SP-type F-functions, respectively.

Moreover, thanks to the meet-in-the-middle approach, our attack leads to low-data complexity.

To demonstrate the usefulness of our approach, we show a key recovery attack on the

8-round reduced CAST-128, which is the best attack with respect to the number of attacked

rounds. Since our approach derives the lower bounds on the numbers of rounds to be secure

under the single secret key setting, it can be considered that we unveil the limitation of

designing an efficient block cipher by a Feistel scheme such as a low-latency cipher.

09:17 [Pub][ePrint]

Profiled side-channel attacks are understood to be powerful when applicable: in the best case when an adversary can comprehensively characterise the leakage, the resulting model leads to attacks requiring a minimal number of leakage traces for success. Such complete\' leakage models are designed to capture the scale, location and shape of the profiling traces, so that any deviation between these and the attack traces potentially produces a mismatch which renders the model unfit for purpose. This severely limits the applicability of profiled attacks in practice and so poses an interesting research challenge: how can we design profiled distinguishers that can tolerate (some) differences between profiling and attack traces?

This submission is the first to tackle the problem head on: we propose distinguishers (utilising unsupervised machine learning methods, but also a down-to-earth\' method combining mean traces and PCA) and evaluate their behaviour across an extensive set of distortions that we apply to representative trace data. Our results show that the profiled distinguishers are effective and robust to distortions to a surprising extent.

06:17 [Pub][ePrint]

Securely sharing the same secret key among multiple parties

is the main concern in symmetric cryptography that is the workhorse

of modern cryptography due to its simplicity and fast speed. Typically asymmetric cryptography is used to set up a shared secret between parties, after which the switch to symmetric cryptography can be made. In this paper, we introduce a novel key exchange protocol based on physical hardware implementation to establish a shared secret between parties rather than relying on mathematical implementation of asymmetric cryptography. In particular, the key exchange is dependent on a new security concept named as virtual proof of reality or simply virtual proof (VP) that enables proof of a physical statement over untrusted digital communication channels between two parties (a prover and a verifier) residing in two separate local systems. We firstly exploit the VP to secure key exchange and further prove it by using experimental data. The key transferred in this protocol is only seen by the prover and hidden from not only the adversary but also the verifier. While only the verifier can successfully discover it.

05:07 [Job][New]

The Computer Science department at the University of Auckland seeks 2 Ph.D. Students to join the cloud security team led by Dr. Giovanni Russello.

This research will take place in a new MBIE-funded Cyber Security STRATUS (Security Technologies Returning Accountability, Transparency and User-centric Services to the Cloud) project and will be in collaboration with University of Waikato, UniTech, the Cloud Security Alliance, and several New Zealand-based industrial partners (https://stratus.org.nz). The aim is to research novel yet practical cloud security tools to be adopted by the industry partners.

The research conducted by the University of Auckland’s team will focus on applied cryptography for retrieval and processing of encrypted data in outsourced and untrusted environments. This involves a substantial program of research to develop, implement and apply to industrial case studies.

Applicants are required to have completed (or be close to completing) a Master degree (or equivalent) with outstanding grades in Computer Science, Mathematics, or closely related areas. Additional knowledge in related disciplines such as, e.g., complexity theory or IT security is welcome.

The candidate should be able not only to design but also implement working prototypes of the crypto scheme developed during the research period.

The STRATUS project will provide a stipend of 25,000 NZD p.a. and cover the costs of the tuition fee for 3 years.