International Association for Cryptologic Research

# IACR News Central

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2015-05-29
09:17 [Pub][ePrint]

Time-lock puzzles, introduced by May, Rivest, Shamir and Wagner, is a mechanism for sending messages to the future\'\'. A sender

can quickly generate a puzzle with a solution $s$ that remains hidden until a moderately large amount of time $t$ has elapsed. The solution $s$ should be hidden from any adversary that runs in time significantly less than $t$, including resourceful parallel adversaries with polynomially many processors.

While the notion of time-lock puzzles has been around for 22 years, there has only been a *single* candidate proposed. Fifteen years ago, Rivest, Shamir and Wagner suggested a beautiful candidate time-lock puzzle based on the assumption that exponentiation modulo an RSA integer is an inherently sequential\'\' computation.

We show that various flavors of {\\em randomized encodings} give rise to time-lock puzzles of varying strengths, whose security can be shown assuming *the existence* of non-parallelizing languages, which are languages that require circuits of depth at least $t$ to decide, in the worst-case. The existence of such languages is necessary for the existence of time-lock puzzles.

We instantiate the construction with different randomized

encodings from the literature, where increasingly better efficiency is obtained based on increasingly stronger cryptographic assumptions, ranging from one-way functions to indistinguishability obfuscation. We also observe that time-lock puzzles imply one-way functions, and thus the reliance on some cryptographic assumption is necessary.

Finally, generalizing the above, we construct other types of puzzles such as *proofs of work* from randomized encodings and a

suitable worst-case hardness assumption (that is necessary for such puzzles to exist).

09:17 [Pub][ePrint]

At CRYPTO 2012, Knellwolf and Khovratovich presented a differential formulation of advanced meet-in-the-middle techniques for preimage attacks on hash functions. They demonstrated the usefulness of their approach by significantly improving the previously best known attacks on SHA-1 from CRYPTO~2009, increasing the number of attacked rounds from a 48-round one-block pseudo-preimage without padding and a 48-round two-block preimage without padding to a 57-round one-block preimage without padding and a 57-round two-block preimage with padding, out of 80 rounds for the full function.

In this work, we exploit further the differential view of meet-in-the-middle techniques and generalize it to higher-order differentials. Despite being an important technique dating from the mid-90\'s, this is the first time higher-order differentials have been applied to meet-in-the-middle preimages. We show that doing so may lead to significant improvements to preimage attacks on hash functions with a simple linear message expansion. We extend the number of attacked rounds on SHA-1 to give a 62-round one-block preimage without padding, a 56-round one-block preimage with padding, and a

62-round two-block preimage with padding. We also apply our framework to the more recent SHA-3 finalist BLAKE and its newer variant BLAKE2, and give an attack for a 2.75-round preimage with padding, and a 7.5-round pseudo-preimage on the compression function.

09:17 [Pub][ePrint]

The ASASA construction is a new design scheme introduced at ASIACRYPT 2014 by Biruykov, Bouillaguet and Khovratovich. Its versatility was illustrated by building two public-key encryption schemes, a secret-key scheme, as well as super S-box subcomponents of a white-box scheme. However one of the two public-key cryptosystems was recently broken at CRYPTO 2015 by Gilbert, Plût and Treger.

As our main contribution, we propose a new algebraic key-recovery attack able to break at once the secret-key scheme as well as the remaining public-key scheme, in time complexity 2^63 and 2^39 respectively (the security parameter is 128 bits in both cases).

Furthermore, we present a second attack of independent interest on the same public-key scheme, which heuristically reduces the problem of breaking the scheme to an LPN instance with tractable parameters. This allows key recovery in time complexity 2^56.

Finally, as a side result, we outline a very efficient heuristic attack on the white-box scheme, which breaks instances claiming 64 bits of security under one minute on a desktop computer.

06:10 [Event][New]

Submission: 15 April 2016
From December 1 to December 2
Location: Kuala Lumpur, Malaysia

2015-05-28
21:17 [Pub][ePrint]

In this paper we detail techniques that can be used to analyze and attack an AES implementation on an FPGA from the primary (i.e., external) side of a switched-mode power supply. Our attack only requires measurements of the duty cycle of the power supply, and then increases the signal-to-noise ratio (SNR) though averaging, deconvolution and wavelet based detrending. The result is an exploitable source of leakage that allows a secret key to be determined from low-frequency power measurements. The techniques and procedures provide a general approach to performing differential power analysis (DPA) from a single point of information for any single hypothesized intermediate value, suggesting their potential for improving other types of side-channel analysis as well.

15:20 [Job][New]

The Security Lab at Swedish Institute of Computer Science (SICS) in Lund and Stockholm is looking for talent post doc researchers in computer and network security. The positions are for 18 months with a monthly salary of 35.000 SEK and the positions can be filled in either Lund or Stockholm. Starting dates are flexible but not later than October 1, 2015. The suitable candidates will work in our EU H2020 financed research projects devoted to 5G security with focus on identity and key management, SDN security as well as in security for Platform as a Service (PaaS) systems (See also the following project page: https://sites.google.com/site/paaswordeu/)

The security Lab at SICS was established in 2009. Since then it has grown from 1 to 12 people. The research is directed toward secure systems design in close co-operation with above leading Swedish companies in the IT and telecommunications businesses as well as Swedish universities such as Royal Institute of Technology in Stockholm and Lund University. The group is active in the areas of embedded systems security, cloud security, access control and communications security. The security lab at SICS consists for the moment of 6 senior researchers (PhD), 3 PhD students and 3 junior researchers with MSc degrees in computer science.

Applicants interested in the positions should provide the following information in pdf format with the application:

- Application letter

- CV

- Publications list

- 3-5 selected full text publications

15:19 [Event][New]

Submission: 15 April 2016
From December 1 to December 2
Location: Kuala Lumpur, Malaysia

03:03 [Event][New]

Submission: 15 April 2016
From December 1 to December 2
Location: Kuala Lumpur, Malaysia

2015-05-27
22:31 [Job][Update]

CloudFlare is looking for a cryptography intern!

CloudFlare is expanding its global footprint. In order to keep our network secure we are investing in technologies to improve the security of our key management infrastructure. We are looking for an ambitious intern to help kickstart one of our cryptographic projects.

Requirements:

• Experience in the theory and implementation of standard cryptographic primitives (AES, RSA, ECC)

• Extensive development experience in C and/or Go

• A deep understanding of reverse engineering techniques

• An unquenchable thirst for understanding and mitigating cryptographic attack vectors

• Outside-the-box thinking and self-starter attitude

Bonus requirements:

• Experience with the cryptol programming language

• Experience with LLVM or other compiler technology

• Knowledge of the theory and implementation of white-box cryptography

Internship length: 4-6 months.

Sound like somewhere you’d thrive? If so, then we’d love to hear from you. Send us your resume and a short paragraph introducing yourself. Please include a brief description of how you solved a customer problem or enhanced a customer\\\'s understanding of a technical service.

CloudFlare is a security company. All prospective employees will be subject to an extensive background check.

CloudFlare is an equal opportunity employer and does not discriminate against any employee or applicant on the basis of age, color, disability, gender, national origin, race, religion, sexual orientation, veteran status, or any classification protected by federal, state, or local law.

• 21:17 [Pub][ePrint]

The security of pairing-based crypto-systems relies on the difficulty to compute discrete logarithms in finite fields GF(p^n) where n is a small integer larger than 1. The state-of-art algorithm is the number field sieve (NFS) together with its many variants. When p has a special form (SNFS), as in many pairings constructions, NFS has a faster variant due to Joux and Pierrot. We present a new NFS variant for SNFS computations, which is better for some cryptographically relevant cases, according to a precise comparison of norm sizes. The new algorithm is an adaptation of Schirokauer\'s variant of NFS based on tower extensions, for which we give a middlebrow presentation.

21:17 [Pub][ePrint]

The prevailing approach for building masked algorithms that can resist higher-order differential power analysis is to develop gadgets, that is, masked gates used as atomic blocks, that securely implement basic operations from the original algorithm, and then to compose these gadgets, introducing refresh operations at strategic places to guarantee that the complete circuit is protected. These compositional principles are embedded in so-called masking transformations, which are used as heuristics to achieve secure composition. Unfortunately, these transformations are seldom proved secure rigorously, and in fact, sometimes yield algorithms that are not secure against higher-order attacks. In this paper, we define a notion of strong simulatability that naturally supports compositional principles. Although this notion is stronger than the notion of simulatability (or perfect simulation) from previous works, we show that it is satisfied by several gadgets from the literature, including the mask refreshing gadget from Duc, Dziembowski and Faust (Eurocrypt 2014), the secure multiplication gadget from Rivain and Prouff (CHES 2010) and the secure multiplication gadget between dependent inputs from Coron et al. (FSE 2013). Then, we exploit a tight connection between strong simulatability and probabilistic information flow policies to define a (fine-grained, incremental) type system that checks (strong) simulatability of algorithms. We use the type system to validate a novel and automated transformation that outputs masked algorithms at arbitrary orders. Finally, we measure the performance of masked algorithms of AES, Keccak-f, Simon, and Speck generated by our transformation. The results are encouraging: for AES, masking at order 5, 20, and 100 respectively incur slowdowns of 100x, 750x, and x1500 w.r.t. the unmasked implementation given as input to our tool.