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).

2014-03-04
22:17 [Pub][ePrint]

RC4 is the most widely used stream cipher around. A lot of modifications of RC4 cipher can be seen in open literature. Most of them enhance the secrecy of the cipher and the security levels have been analyzed theoretically by using mathematics. In this paper, a new effective RC4 cipher is proposed and the security analysis has been done using Shannon\'s Secrecy theories where numerical values are obtained to depict the secrecy. The proposed cipher is a combination of Improved RC4 cipher proposed by Jian Xie et al and modified RC4 cipher proposed by T.D.B Weerasinghe, which were published prior to this work. Combination is done in such a way that the concept used in the modified RC4 algorithm is used in the Improved RC4 cipher by Jian Xie et al. Importantly, an immense improvement of performance and secrecy are obtained by this combination. Hence this particular modification of RC4 cipher can be used in software applications where there is a need to improve the throughput as well as secrecy.

22:17 [Pub][ePrint]

Physically unclonable functions (PUFs) exploit the unavoidable manufacturing variations of an integrated circuit (IC). Their input-output behavior serves as a unique IC \'fingerprint\'. Therefore, they have been envisioned as an IC authentication mechanism, in particular for the subclass of so-called strong PUFs. The protocol proposals are typically accompanied with two PUF promises: lightweight and an increased resistance against physical attacks. In this work, we review eight prominent proposals in chronological order: from the original strong PUF proposal to the more complicated converse and slender PUF proposals. The novelty of our work is threefold. First, we employ a unied notation and framework for ease of understanding. Second, we initiate direct comparison between protocols, which has been neglected in each of the proposals. Third, we reveal numerous security and practicality issues. To such an extent, that we can not support the use of any proposal in its current form. All proposals aim to compensate the lack of cryptographic properties of the strong PUF. However, proper compensation seems to oppose the lightweight objective.

22:17 [Pub][ePrint]

Non-malleable codes are a natural relaxation of error correcting/detecting codes that have useful applications in the context of tamper resilient cryptography. Informally, a code is non-malleable if an adversary trying to tamper with an encoding of a given message can only leave it unchanged or modify it to the encoding of a completely unrelated value. This paper introduces an extension of the

standard non-malleability security notion - so-called continuous non-malleability - where we allow the adversary to tamper continuously with an encoding. This is in contrast to the standard notion of

non-malleable codes where the adversary only is allowed to tamper a single time with an encoding. We show how to construct continuous non-malleable codes in the common split-state model where an encoding consist of two parts and the tampering can be arbitrary but has to be independent with both parts. Our main contributions are outlined below:

1. We propose a new uniqueness requirement of split-state codes which states that it is computationally hard to find two codewords C = (X0;X1) and C0 = (X0;X1\') such that both codewords are valid, but X0 is the same in both C and C0. A simple attack shows that uniqueness

is necessary to achieve continuous non-malleability in the split-state model. Moreover, we illustrate that none of the existing constructions satisfies our uniqueness property and hence is not secure in the continuous setting.

2. We construct a split-state code satisfying continuous non-malleability. Our scheme is based

on the inner product function, collision-resistant hashing and non-interactive zero-knowledge

proofs of knowledge and requires an untamperable common reference string.

3. We apply continuous non-malleable codes to protect arbitrary cryptographic primitives against tampering attacks. Previous applications of non-malleable codes in this setting required to

perfectly erase the entire memory after each execution and and required the adversary to be restricted in memory. We show that continuous non-malleable codes avoid these restrictions.

10:17 [Pub][ePrint]

In this paper, we investigate the encryption quality of the robust chaotic block cipher (RCBC) algorithm; which is based on chaotic map. In addition to visual inspection of images encryption testing, five analytical metrics are developed for analyzing the encryption quality. These metrics are used to evaluate several encrypted images factors include: maximum deviation, irregular deviation, information entropy, correlation coefficients, and avalanche effect. Comparison of the encryption quality for RCBC, RC6 and RC5 implantations to digital images are performed. In the experimental results, we have made our tests using color images Lena, Cman, and Peppers, each of size 512x512 pixels, as the original images (plain-images). Results show better quality of the RCBC.

10:17 [Pub][ePrint]

The j-lanes tree hashing is a tree mode that splits an input message to j slices, computes j independent digests of each slice, and outputs the hash value of their concatenation. The j-pointers tree hashing is a similar tree mode that receives, as input, j pointers to j messages (or slices of a single message), computes their digests and outputs the hash value of their concatenation. Such modes have parallelization capabilities on a hashing process that is serial by nature. As a result, they have performance advantage on modern processor architectures. This paper provides precise specifications for these hashing modes, proposes a setup for appropriate IV\'s definition, and demonstrates their performance on the latest processors. Our hope is that it would be useful for standardization of these modes.

09:19 [Event][New]

Submission: 27 May 2014
From December 7 to December 11
Location: Kaohsiung, Taiwan

09:18 [Event][New]

Submission: 27 May 2014
From December 7 to December 11
Location: Kaohsiung, Taiwan

01:17 [Pub][ePrint]

Verifiable computation (VC) enables thin clients to efficiently verify the computational results produced by a powerful server. Although VC was initially considered to be mainly of theoretical interest, over the last two years, impressive progress has been made on implementing VC. Specifically, we now have open-source implementations of VC systems that can handle all classes of computations expressed either as circuits or in the RAM model. However, despite this very encouraging progress, new enhancements in the design and implementation of VC protocols are required in order to achieve truly practical VC for real-world applications. In this work, we show that for functionalities that can be expressed efficiently in terms of set operations (e.g., a subset of SQL queries) VC can be enhanced to become drastically more practical: We present the design and prototype implementation of a novel VC scheme that achieves orders of magnitude speed-up in comparison with the state of the art. Specifically, we build and evaluate TRUESET, a system that can verifiably compute any polynomial-time function expressed as a circuit consisting of \"set gates\" such as union, intersection, difference and set cardinality. Moreover, TRUESET supports hybrid circuits consisting of both set gates and traditional arithmetic gates and, therefore, does not lose any of the expressiveness of the previous schemes (allowing, at the same time, the user to choose the most efficient way to represent different parts of a computation task). By expressing set computations as polynomial operations and introducing a novel Quadratic Polynomial Program technique, TRUESET achieves prover performance speed-up ranging from 30x to 150x and yields up to 97% evaluation key size reduction.

01:17 [Pub][ePrint]

We apply the Flush-Reload side-channel attack based on cache hits/misses to extract a small amount of data from OpenSSL ECDSA signature requests. We then apply a standard\'\' lattice technique to extract the private key, but unlike previous attacks we are able to make use of the side-channel information from almost all of the observed executions. This means we obtain private key recovery by observing a relatively small number of executions, and by expending a relatively small amount of post-processing via lattice reduction. We demonstrate our analysis via experiments using the curve secp256k1 used in the Bitcoin protocol. In particular we show that with as little as 200 signatures we are able to achieve a reasonable level of success in recovering the secret key for a 256-bit curve. This is significantly better than prior methods of applying lattice reduction techqniques to similar side channel information.

01:17 [Pub][ePrint]

Signcryption is a useful paradigm which simultaneously offers both the functions of encryption and signature in a single logic step. It would be interesting to make signcryption certificateless to ease the heavy burden of certificate management in traditional public key cryptography (PKC) and solve the key escrow problem in Identity-based public key cryptography (ID-PKC). Most certificateless signcryption (CL-SC) schemes are constructed in the random oracle model instead of the standard model. By exploiting Bellare and Shoup\'s one-time signature, Hwang et al.\'s certificateless encryption and Li et al.\'s identity-based signcryption, this paper proposes a new CL-SC scheme secure in the standard model. It is proven that our CL-SC scheme satisfies semantic security and unforgeability against the outside adversary and malicious-but-passive key generation center (KGC) assuming the hardness of bilinear decision Diffie-Hellman (BDDH) and computational Diffie-Hellman (CDH) problems. Our security proofs do not depend on random oracles.

01:17 [Pub][ePrint]

Amongst areas of cryptographic research, there has recently been a widening interest for code-based cryptosystems and their implementations. Besides the {\\it a priori} resistance to quantum computer attacks, they represent a real alternative to the currently used cryptographic schemes. In this paper we consider the implementation of the Stern authentication scheme and one recent variation of this scheme by Aguilar {\\it et al.}. These two schemes allow public authentication and public signature with public and private keys of only a few hundreds bits. The contributions of this paper are twofold: first, we describe how to implement a code-based signature in a constrained device through the Fiat-Shamir paradigm, in particular we show how to deal with long signatures. Second, we implement and explain new improvements for code-based zero-knowledge signature schemes. We describe implementations for these signature and authentication schemes, secured against side channel attacks, which drastically improve the previous implementation presented at Cardis 2008 by Cayrel {\\it et al.}. We obtain a factor 3 reduction of speed and a factor of about 2 for the length of the signature. We also provide an extensive comparison with RSA signatures.