New Second Preimage Attacks on Dithered Hash Functions with Low Memory Complexity

Dithered hash functions were proposed by Rivest as a method to mitigate second preimage attacks on Merkle-Damgard hash functions. Despite that, second preimage attacks against dithered hash functions were proposed by Andreeva et al. One issue with these second preimage attacks is their huge memory requirement in the precomputation and the online phases. In this paper, we present new second preimage attacks on the dithered Merkle-Damgard construction. These attacks consume significantly less memory in the online phase (with a negligible increase in the online time complexity) than previous attacks. For example, in the case of MD5 with the Keranen sequence, we reduce the memory complexity from about 2^51 blocks to about 2^26.7 blocks (about 545 MB). We also present an essentially memoryless variant of Andreeva et al. attack. In case of MD5-Keranen or SHA1-Keranen, the offline and online memory complexity is 2^15.2 message blocks (about 188–235 KB), at the expense of increasing the offline time complexity

On the Design of Secure and Fast Double Block Length Hash Functions

In this work the security of the rate-1 double block length hash functions, which based on a block cipher with a block length of n-bit and a key length of 2n-bit, is reconsidered. Counter-examples and new attacks are presented on this general class of double block length hash functions with rate 1, which disclose uncovered flaws in the necessary conditions given by Satoh et al. and Hirose. Preimage and second preimage attacks are presented on Hirose's two examples which were left as an open problem. Therefore, although all the rate-1 hash functions in this general class are failed to be optimally (second) preimage resistant, the necessary conditions are refined for ensuring this general class of the rate-1 hash functions to be optimally secure against the collision attack. In particular, two typical examples, which designed under the refined conditions, are proven to be indifferentiable from the random oracle in the ideal cipher model. The security results are extended to a new class of double block length hash functions with rate 1, where one block cipher used in the compression function has the key length is equal to the block length, while the other is doubled

New Attacks on the Concatenation and XOR Hash Combiners

We study the security of the concatenation combiner $H_1(M) \| H_2(M)$ for two independent iterated hash functions with $n$-bit outputs that are built using the Merkle-Damgård construction. In 2004 Joux showed that the concatenation combiner of hash functions with an $n$-bit internal state does not offer better collision and preimage resistance compared to a single strong $n$-bit hash function. On the other hand, the problem of devising second preimage attacks faster than $2^n$ against this combiner has remained open since 2005 when Kelsey and Schneier showed that a single Merkle-Damgård hash function does not offer optimal second preimage resistance for long messages. In this paper, we develop new algorithms for cryptanalysis of hash combiners and use them to devise the first second preimage attack on the concatenation combiner. The attack finds second preimages faster than $2^n$ for messages longer than $2^{2n/7}$ and has optimal complexity of $2^{3n/4}$. This shows that the concatenation of two Merkle-Damgård hash functions is not as strong a single ideal hash function. Our methods are also applicable to other well-studied combiners, and we use them to devise a new preimage attack with complexity of $2^{2n/3}$ on the XOR combiner $H_1(M) \oplus H_2(M)$ of two Merkle-Damgård hash functions. This improves upon the attack by Leurent and Wang (presented at Eurocrypt 2015) whose complexity is $2^{5n/6}$ (but unlike our attack is also applicable to HAIFA hash functions). Our algorithms exploit properties of random mappings generated by fixing the message block input to the compression functions of $H_1$ and $H_2$. Such random mappings have been widely used in cryptanalysis, but we exploit them in new ways to attack hash function combiners

On the Security of Iterated Hashing based on Forgery-resistant Compression Functions

In this paper we re-examine the security notions suggested for hash functions, with an emphasis on the delicate notion of second preimage resistance. We start by showing that, in the random oracle model, both Merkle-Damgaard and HAIFA achieve second preimage resistance beyond the birthday bound, and actually up to the level of known generic attacks, hence demonstrating the optimality of HAIFA in this respect. We then try to distill a more elementary requirement out of the compression function to get some insight on the properties it should have to guarantee the second preimage resistance of its iteration. We show that if the (keyed) compression function is a secure FIL-MAC then the Merkle-Damgaard mode of iteration (or HAIFA) still maintains the same level of second preimage resistance. We conclude by showing that this ``new\u27\u27 assumption (or security notion) implies the recently introduced Preimage-Awareness while ensuring all other classical security notions for hash functions

A New Proposal Against the Main of Generic Attacks

This paper presents a effcient proposal for iterating hash functions to prevent the main of generic attacks such as Multicollisions Attack,Second Preimage Attack and Herding Attack.Based on this proposal,it’s possible that a secure hash function can be built with iterating compression functions . The proposal mainly contains a method called ” Shifting Whole Message”,it regroups the cascaded messages to be new blocks and makes the known results of the pre-computed blocks noneffective

Cryptanalysis of Reduced-Round Whirlwind (Full Version)

The \texttt{Whirlwind} hash function, which outputs a 512-bit digest, was designed by Barreto $et\ al.$ and published by \textit{Design, Codes and Cryptography} in 2010. In this paper, we provide a thorough cryptanalysis on \texttt{Whirlwind}. Firstly, we focus on security properties at the hash function level by presenting (second) preimage, collision and distinguishing attacks on reduced-round \texttt{Whirlwind}. In order to launch the preimage attack, we have to slightly tweak the original Meet-in-the-Middle preimage attack framework on \texttt{AES}-like compression functions by partially fixing the values of the state. Based on this slightly tweaked framework, we are able to construct several new and interesting preimage attacks on reduced-round \texttt{Whirlpool} and \texttt{AES} hashing modes as well. Secondly, we investigate security properties of the reduced-round components of \texttt{Whirlwind}, including semi-free-start and free-start (near) collision attacks on the compression function, and a limited-birthday distinguisher on the inner permutation. As far as we know, our results are currently the best cryptanalysis on \texttt{Whirlwind}

Security proofs for the MD6 hash function mode of operation

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2008.Includes bibliographical references (p. 79-82).In recent years there have been a series of serious and alarming cryptanalytic attacks on several commonly-used hash functions, such as MD4, MD5, SHA-0, and SHA1 [13, 38]. These culminated with the celebrated work of Wang, Yin, and Yu from 2005, which demonstrated relatively efficient methods for finding collisions in the SHA-1 hash function [37]. Although there are several cryptographic hash functions - such as the SHA-2 family [28] - that have not yet succumbed to such attacks, the U.S. National Institute of Standards and Technology (NIST) put out a call in 2007 for candidate proposals for a new cryptographic hash function family, to be dubbed SHA-3 [29]. Hash functions are algorithms for converting an arbitrarily large input into a fixed-length message digest. They are typically composed of a compression function or block cipher that operate on fixed-length pieces of the input and a mode of operation that governs how apply the compression function or block cipher repeatedly on these pieces in order to allow for arbitrary-length inputs. Cryptographic hash functions are furthermore required to have several important and stringent security properties including (but not limited to) first-preimage resistance, second-preimage resistance, collision resistance, and for keyed hash functions, pseudorandomness. This work presents proofs of security for the mode of operation of the MD6 cryptographic hash function [32] - a candidate for the SHA-3 competition - which differs greatly from the modes of operation of many commonly-used hash functions today (MD4, MD5, as well as the SHA family of hash functions.) In particular, we demonstrate provably that the mode of operation used in MD6 preserves some cryptographic properties of the compression function - that is, assuming some ideal conditions about the compression function used, the overall MD6 hash function is secure as well.by Christopher Yale Crutchfield.S.M