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09:17 [Pub][ePrint] New Generic Attacks Against Hash-based MACs, by Gaëtan Leurent and Thomas Peyrin and Lei Wang

  In this paper we study the security of hash-based MAC algorithms (such as HMAC and NMAC) above the birthday bound. Up to the birthday bound, HMAC and NMAC are proven to be secure under reasonable assumptions on the hash function. On the other hand, if an $n$-bit MAC is built from a hash function with a $l$-bit state ($l \\ge n$), there is a well-known existential forgery attack with complexity $2^{l/2}$. However, the remaining security after $2^{l/2}$ computations is not well understood. In particular it is widely assumed that if the underlying hash function is sound, then a generic universal forgery attack should still require $2^{n}$ computations and some distinguishing (e.g. distinguishing-H but not distinguishing-R) and state-recovery attacks should still require $2^{l}$ (or $2^k$ if $k < l$) computations.

In this work, we show that above the birthday bound, hash-based MACs offer significantly less security than previously believed. Our main result is a generic distinguishing-H and state-recovery attack against hash-based MACs with a complexity of only $\\tilde O(2^{l/2})$. In addition, we show a key-recovery attack with complexity $\\tilde O(2^{3l/4})$ against HMAC used with a hash functions with an internal checksum, such as GOST. This surprising result shows that the use of a checksum might actually weaken a hash function when used in a MAC. We stress that our attacks are generic, and they are in fact more efficient than some previous attacks proposed on MACs instantiated with concrete hash functions.

We use techniques similar to the cycle-detection technique proposed by Peyrin et al. at Asiacrypt 2012 to attack HMAC in the related-key model. However, our attacks works in the single-key model for both HMAC and NMAC, and without restriction on the key size.

09:17 [Pub][ePrint] Towards Symmetric Functional Encryption for Regular Languages with Predicate Privacy, by Fu-Kuo Tseng and Rong-Jaye Chen and Bao-Shuh Paul Lin

  We present a symmetric-key predicate-only functional encryption system, SP-FE, which supports functionality for regular languages describe by deterministic finite automata. In SP-FE, a data owner can encrypt a string of symbols as encrypted symbols for matching. Later, the data owner can generate predicate tokens of the transitions in a deterministic finite automaton. The server with these tokens can decrypt a sequence of encrypted symbols correctly and transfer from one state to another accordingly. If the final state belongs to the set of accept states, the server takes assigned operations or returns the corresponding encrypted data. We have proven SP-FE preserves both plaintext privacy and predicate privacy through security analysis and security games. To achieve predicate privacy, we put bounds on the length of a string and the number of states of a DFA. Due to these restrictions, SP-FE can capture only finite languages. Finally, we present the performance analysis of SP-FE and mention possible future work.

06:17 [Forum] [2014 Reports] 2014/377 by Orr

  This looks like a paper of "how to tranform secret key algorithm into public key one using obfuscation". Take AES-X, and obfuscate. From: 2014-02-06 05:46:14 (UTC)

15:17 [Pub][ePrint] Jacobian Coordinates on Genus 2 Curves, by Huseyin Hisil and Craig Costello

  This paper presents a new projective coordinate system and new explicit algorithms which together boost the speed of arithmetic in the divisor class group of genus 2 curves. The proposed formulas generalise the use of Jacobian coordinates on elliptic curves, and their application improves the speed of performing cryptographic scalar multiplications in Jacobians of genus 2 curves over prime fields by an approximate factor of 1.25x. For example, on a single core of an Intel Core i7-3770M (Ivy Bridge), we show that replacing the previous best formulas with our new set improves the cost of generic scalar multiplications from 243,000 to 195,000 cycles, and drops the cost of specialised GLV-style scalar multiplications from 166,000 to 129,000 cycles.

15:17 [Pub][ePrint] Chaskey: An Efficient MAC Algorithm for 32-bit Microcontrollers, by Nicky Mouha and Bart Mennink and Anthony Van Herrewege and Dai Watanabe and Bart Preneel and Ingrid Verbauwhede

  We propose Chaskey: a very efficient Message Authentication Code (MAC) algorithm for 32-bit microcontrollers. It is intended for applications that require 128-bit security, yet cannot implement standard MAC algorithms because of stringent requirements on speed, energy consumption, or code size. Chaskey is a permutation-based MAC algorithm that uses the Addition-Rotation-XOR (ARX) design methodology. We formally prove that Chaskey is secure in the standard model, based on the security of an underlying Even-Mansour block cipher. Chaskey is designed to perform well on a wide range of 32-bit microcontrollers. Our benchmarks show that on the ARM Cortex-M3/M4, our Chaskey implementation reaches a speed of 7.0 cycles/byte, compared to 89.4 cycles/byte for AES-128-CMAC. For the ARM Cortex-M0, our benchmark results give 16.9 cycles/byte and 136.5 cycles/byte for Chaskey and AES-128-CMAC respectively.

15:17 [Pub][ePrint] New candidates for multivariate trapdoor functions, by Jaiberth Porras, John B. Baena, Jintai Ding

  We present a new method for building pairs of HFE polynomials of high degree, such that the map constructed with such a pair is easy to invert. The inversion is accomplished using a low degree polynomial of Hamming weight three, which is derived from a special reduction via Hamming weight three polynomials produced by these two HFE polynomials. This allows us to build new candidates for multivariate trapdoor functions in which we use the pair of HFE polynomials to fabricate the core map. We performed the security analysis for the case where the base field is $GF(2)$ and showed that these new trapdoor functions have high degrees of regularity, and therefore they are secure against the direct algebraic attack. We also give theoretical arguments to show that these new trapdoor functions over $GF(2)$ are secure against the MinRank attack as well.

15:17 [Pub][ePrint] Finding collisions for MD4 hash algorithm using hybrid algorithm, by Marko Carić

  The modification of message that meets the sufficient conditions for

collision is found in the last step of differential attack proposed

by Wang et all. (2005) on MD4 hash algorithm. Here we show how this

attack phase, finding a collision starting from the list of

sufficient conditions for the collision, can be implemented using a

combination of two algorithms - evolutionary algorithm and hill

climbing. Hybridization of evolutionary algorithm and hill climbing

is a well-known technique for improving solutions, but it isn\'t

applied to this domain (at least by information that author has


15:17 [Pub][ePrint] Accelerating NTRU based Homomorphic Encryption using GPUs, by Wei Dai and Yark{\\i}n Dor\\\"{o}z and Berk Sunar

  In this work we introduce a large polynomial arithmetic library optimized for Nvidia GPUs to support fully homomorphic encryption schemes. To realize the large polynomial arithmetic library we convert the polynomial with large coefficients using the Chinese Remainder Theorem into many polynomials with small coefficients, and then carry out modular multiplications in the residue space using a custom developed discrete Fourier transform library. We further extend the library to support the homomorphic evaluation operations, i.e. addition, multiplication, and relinearization, in an NTRU based somewhat homomorphic encryption library. Finally, we put the library to use to evaluate homomorphic evaluation of two block ciphers: Prince and AES, which show 2.57 times and 7.6 times speedup, respectively, over an Intel Xeon software implementation.

15:17 [Pub][ePrint] Black-Box Non-Black-Box Zero Knowledge, by Vipul Goyal and Rafail Ostrovsky and Alessandra Scafuro and Ivan Visconti

  Motivated by theoretical and practical interest, the challenging task of designing crypto- graphic protocols having only black-box access to primitives has generated various breakthroughs in the last decade. Despite such positive results, even though nowadays we know black-box constructions for secure two-party and multi-party computation even in constant rounds, there still are in Cryptography several constructions that critically require non-black-box use of primitives in order to securely realize some fundamental tasks. As such, the study of the gap between black-box and non-black-box constructions still includes major open questions.

In this work we make progress towards filling the above gap. We consider the case of black- box constructions for computations requiring that even the size of the input of a player remains hidden. We show how to commit to a string of arbitrary size and to prove statements over the bits of the string. Both the commitment and the proof are succinct, hide the input size and use standard primitives in a black-box way. We achieve such a result by giving a black-box construction of an extendable Merkle tree that relies on a novel use of the \"MPC in the head\" paradigm of Ishai et al. [STOC 2007].

We show the power of our new techniques by giving the first black-box constant-round public-coin zero knowledge argument for NP.

To achieve this result we use the non-black-box simulation technique introduced by Barak [FOCS 2001], the PCP of Proximity introduced by Ben-Sasson et al. [STOC 2004], together with a black-box public-coin witness indistinguishable universal argument that we construct along the way.

Additionally we show the first black-box construction of a generalization of zero-knowledge sets introduced by Micali et al. [FOCS 2003]. The generalization that we propose is a strengthening that requires both the size of the set and the size of the elements of the set to remain private.

15:17 [Pub][ePrint] MuR-DPA: Top-down Levelled Multi-replica Merkle Hash Tree Based Secure Public Auditing for Dynamic Big Data Storage on Cloud, by Chang Liu, Rajiv Ranjan, Chi Yang, Xuyun Zhang, Lizhe Wang, Jinjun Chen

  Big data and its applications are attracting more and more research interests in recent years. As the new generation distributed computing platform, cloud computing is believed to be the most potent platform. With the data no longer under users\' direct control, data security in cloud computing is becoming one of the most obstacles of the proliferation of cloud. In order to improve service reliability and availability, storing multiple replicas along with original datasets is a common strategy for cloud service providers. Public data auditing schemes allow users to verify their outsourced data storage without having to retrieve the whole dataset. However, existing data auditing techniques suffers from efficiency and security problems. First, for dynamic datasets with multiple replicas, the communication overhead for update verification is very large, because verification for each update requires O(logn) communication complexity and update of all replicas. Second, to the best of our knowledge, there is no existing integrity verification schemes can provide public auditing and authentication of block indices at the same time. Without authentication of block indices, the server can build a valid proof based on data blocks other than the block client requested to verify. In order to address these problems, in this paper, we present a novel public auditing scheme named MuR-DPA. The new scheme incorporated a novel authenticated data structure based on the Merkle hash tree, which we name as MR-MHT. For support of full dynamic data updates, authentication of block indices and efficient verification of updates for multiple replicas at the same time, the level values of nodes in MR-MHT are generated in a top-down order, and all replica blocks for each data block are organized into a same replica sub-tree. Compared to existing integrity verification and public auditing schemes, theoretical analysis and experimental results show that the MuR-DPA scheme can not only incur much less communication overhead for both update and verification of datasets with multiple replicas, but also provide enhanced security against dishonest cloud service providers.

15:17 [Pub][ePrint] The Randomized Iterate Revisited - Almost Linear Seed Length PRGs from A Broader Class of One-way Functions, by Yu Yu and Dawu Gu and Xiangxue Li

  We revisit ``the randomized iterate\'\' technique that was originally used by Goldreich, Krawczyk, and Luby (SICOMP 1993) and refined by Haitner, Harnik and Reingold (CRYPTO 2006) in constructing pseudorandom generators (PRGs) from regular one-way functions (OWFs). We abstract out a technical lemma with connections to several recent work on cryptography with imperfect randomness, which provides an arguably simpler and more modular proof for the Haitner-Harnik-Reingold PRGs from regular OWFs.

We extend the approach to a more general construction of PRGs with seed length $O(n{\\log}n)$ from a broader class of OWFs. More specifically, consider an arbitrary one-way function $f$ whose range is divided into sets $\\Y_1$, $\\Y_2$, $\\ldots$, $\\Y_n$ where each $\\Y_i\\eqdef\\{y:2^{i-1}\\le|f^{-1}(y)|