International Association for Cryptologic Research

# IACR News Central

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2015-07-05
18:17 [Pub][ePrint]

We extend the reach of functional encryption schemes that are provably secure under simple assumptions against unbounded collusion to include function-hiding inner product schemes. Our scheme is a private key functional encryption scheme, where ciphertexts correspond to vectors $\\vec{x}$, secret keys correspond to vectors $\\vec{y}$, and a decryptor learns $\\langle \\vec{x}, \\vec{y} \\rangle$. Our scheme employs asymmetric bilinear maps and relies only on the SXDH assumption to satisfy a natural indistinguishability-based security notion where arbitrarily many key and ciphertext vectors can be simultaneously changed as long as the key-ciphertext dot product relationships are all preserved.

18:17 [Pub][ePrint]

We propose a new unified point compression format for Edwards, Twisted Edwards and Montgomery curves over large-characteristic fields, which effectively divides the curve\'s cofactor by 4 at very little cost to performance. This allows cofactor-4 curves to efficiently implement prime-order groups.

18:17 [Pub][ePrint]

This paper presents a generic method for turning passively secure protocols into protocols secure against covert attacks, adding an offline preprocessing and a cheap post-execution verification phase. The execution phase, after which the computed result is already available to the parties, has only negligible overhead.

Our method uses shared verification based on precomputed multiplication triples. Such triples are often used to make the protocol execution itself faster, but in this work we make use of these triples especially for verification. The verification preserves the privacy guarantees of the original protocol, and it can be straightforwardly applied to protocols over finite rings, even if the same protocol performs its computation over several distinct rings at once.

18:17 [Pub][ePrint]

Emerging smart contract systems over decentralized cryp-

tocurrencies allow mutually distrustful parties to transact

safely with each other without trusting a third-party inter-

mediary. In the event of contractual breaches or aborts, the

decentralized blockchain ensures that other honest parties

obtain commesurate remuneration. Existing systems, how-

ever, lack transactional privacy. All transactions, including

flow of money between pseudonyms and amount trasacted,

are exposed in the clear on the blockchain.

We present Hawk, a decentralized smart contract system

that does not store financial transactions in the clear on

the blockchain, thus retaining transactional privacy from the

public\'s view. A Hawk programmer can write a private smart

contract in an intuitive manner without having to implement

cryptography, and our compiler automatically generates an

efficient cryptographic protocol where contractual parties in-

teract with the blockchain, using cryptographic primitives

such as succint zero-knowledge proofs.

To formally define and reason about the security of our

protocols, we are the first to formalize the blockchain model

of secure computation. The formal modeling is of indepen-

formal model when designing interesting applications atop

decentralized blockchains.

18:17 [Pub][ePrint]

This paper explores some attacks that someone with a Quantum Computer may be able to perform against NTRUEncrypt, and in particular NTRUEncrypt as implemented by the publicly available library from Security Innovation. We show four attacks that an attacker with a Quantum Computer might be able to perform against encryption performed by this library. Two of these attacks recover the private key from the public key with less effort than expected; in one case taking advantage of how the published library is implemented, and the other, an academic attack that works against four of the parameter sets defined for NTRUEncrypt. In addition, we also show two attacks that are able to recover plaintext from the ciphertext and public key with less than expected effort. This has potential implications on the use of NTRU within TOR, as suggested by Whyte and Schanck

18:17 [Pub][ePrint]

The original specification of EdDSA was suitable only for finite fields Fq with q mod 4 = 1. The main purpose of this document is to extend EdDSA to allow finite fields Fq with any odd q. This document also extends EdDSA to support prehashing, i.e., signing the hash of a message.

09:17 [Forum]

It seems like a guessing. Do you have a formal prove of "... for each 8-bit word x of the state/input plaintext there is a mapping (although secret) to another word y of the ciphertext, independently from the adjacent words."? From: 2015-05-07 09:03:21 (UTC)

03:17 [Forum]

I have had a brief look into that "new cipher", and it seems to me that it is weak. The reason is that for each 8-bit word x of the state/input plaintext there is a mapping (although secret) to another word y of the ciphertext, independently from the adjacent words. This is true if we remove the very first and the very last arithmetic addition modulo 2^64, and it is true for the full version with a very high probability (probability of the carry bit). The mapping x->y of each word can be seen as an S-box for that individual mapping, and it is constant for the same key/iv setup. After roughly 256+ known pairs plaintext-ciphertext the mapping is then revealed (even without having to derive the secret key, although this might also be possible with a little more thinking). From: 2015-05-07 00:27:07 (UTC)

2015-07-03
18:42 [Job][New]

The University of Luxembourg is offering a Ph.D. student position in one of the topics:

• cryptofinance, cryptocurrencies
• anonymity and privacy
• cybersecurity

Applicants interested in symmetric cryptography, authenticated encryption will be also considered.

Profile:

• An M.Sc. in Computer Science or Applied Mathematics (some background in Economics/Finance is a plus)
• GPA > 85%
• Fluent written and verbal communication skills in English are mandatory.

We offer international research environment and competitive salary. The position is available from the 1-October 2015. Applications will be considered upon receipt, therefore applying before the deadline is encouraged.

16:34 [Job][New]

* The Chair for Security in Distributed Systems, computer science Hochschule Offenburg, Germany, offers a full-time PhD positions:

* The position involves research in the area of IT-security within the project PAL SAaaS \'Building Triangular Trust for Secure Cloud Auduting\' in cooperation with the University of Mannheim (Prof. Dr. Frederik Armknecht).

The successful candidate is expected to contribute to research in IT-Security and applied cryptography for Cloud Security.

Besides other cloud security related aspects topics of interest for the open positions are

- application of homomorphic cryptographic primitives for secure cloud storage,

- applying the above schemes to the auditing process for cloud services.

* The position is available from August on and is fully funded. The salary scale is TV-L E13.

The gross income depends on the candidate\'s experience level. At the lowest level it corresponds to approx. 40,000 EUR per year.

* Contracts are offered for three years.

* She or he is given the possiblity to carry out a Ph.D.

* The successful candidate should have a Master\'s degree in Computer Science, Mathematics, Information Security, or a related field.

Deep Knowledge in cryptography is not a must but an asset.

* The deadline for applications is July 20, 2015. However, late applications will be considered until the position is filled.

Please send your application with reference number to Prof. Dr. Dirk Westhoff (dirk DOT westhoff AT hs-offenburg DOT de).

09:17 [Pub][ePrint]

The traditional fault analysis techniques developed over the past decade rely on a fault

model, a rigid assumption about the nature of the fault. A practical challenge for all faults attacks is to identify a fault injection method that achieves the presumed fault model.

In this paper, we analyze a class of more recently proposed fault analysis techniques,

which adopt a biased fault model. Biased fault attacks enable

a more flexible fault model, and are therefore easier to adopt to practice.

The purpose of our analysis is to evaluate the relative efficiency of several recently proposed biased-fault attacks, including Fault Sensitivity Analysis (FSA), Non-Uniform Error Value Analysis (NUEVA), Non-Uniform Faulty Value Analysis (NUFVA), and Differential Fault Intensity Analysis (DFIA).

We compare the relative performance of each technique in a common framework, using a common circuit and using a common fault injection method. We show that, for an identical circuit and an identical fault injection method, the number of faults per attack greatly varies according with the analysis technique.

In particular, DFIA is more efficient than FSA, and FSA is more efficient than both NUEVA and NUFVA. In terms of number of fault injections until full key disclosure, for a typical case, FSA uses 8x more faults than DFIA, and NUEVA uses 33x more faults than DFIA. Hence, the post-processing technique selected in a biased-fault attack has a significant impact on the probability of a successful attack.