A one-way hashing algorithm is a deterministic algorithm that compresses an arbitrary long message into a value of specified length. The output value represents the fingerprint or digest of the message. A cryptographically useful property of a one-way hashing algorithm is that it is infeasible to find two distinct messages that have the same fingerprint. This paper proposes a one-way hashing algorithm called HAVAL. HAVAL compresses a message of arbitrary length into a fingerprint of 128, 160, 192, 224 or 256 bits. In addition, HAVAL has a parameter that controls the number of passes a message block (of 1024 bits) is processed. A message block can be processed in 3, 4 or 5 passes. By combining output length with pass, we can provide fifteen (15) choices for practical applications where different levels of security are required. The algorithm is very efficient and particularly suited for 32-bit computers which predominate the current workstation market. Experiments show that HAVAL is 60%...

In recent years, methods based on lattice reduction have been used repeatedly for the cryptanalytic attack of various systems. Even if they do not rest on highly sophisticated theories, these methods may look a bit intricate to the practically oriented cryptographers, both from the mathematical and the algorithmic point of view. The aim of the present paper is to explain what can be achieved by lattice reduction algorithms, even without understanding of the actual mechanisms involved. Two examples are given, one of them being the attack devised by the second named author against Knuth's truncated linear congruential generator, which has been announced a few years ago and appears here for the first time in journal version.

Abstract We point out that the seemingly strong pseudorandom oracle preserving (PRO-Pr) propertyof hash function domain-extension transforms defined and implemented by Coron et. al. [12] can actually weaken our guarantees on the hash function, in particular producing a hash functionthat fails to be even collision-resistant (CR) even though the compression function to which the transform is applied is CR. Not only is this true in general, but we show that all the transformspresented in [12] have this weakness. We suggest that the appropriate goal of a domain extension transform for the next generation of hash functions is to be multi-property preserving, namelythat one should have a single transform that is simultaneously at least collision-resistance preserving, pseudorandom function preserving and PRO-Pr. We present an efficient new transformthat is proven to be multi-property preserving in this sense.

Abstract. In this paper we present a new scheme for constructing universal one-way hash functions that hash arbitrarily long messages out of universal one-way hash functions that hash fixed-length messages. The new construction is extremely simple and is also very efficient, yielding shorter keys than previously proposed composition constructions. 1

We propose randomized hashing as a mode of operation for cryptographic hash functions intended for use with standard digital signatures and without necessitating of any changes in the internals of the underlying hash function (e.g., the SHA family) or in the signature algorithms (e.g., RSA or DSA). The goal is to free practical digital signature schemes from their current reliance on strong collision resistance by basing the security of these schemes on significantly weaker properties of the underlying hash function, thus providing a safety net in case the (current or future) hash functions in use turn out to be less resilient to collision search than initially thought. We design a specific mode of operation that takes into account engineering considerations (such as simplicity, efficiency and compatibility with existing implementations) as well as analytical soundness. Specifically, the scheme entails unmodified use of the hash function with randomization applied only to the message before it is input to the hash function. We formally show the sufficiency of an assumption significantlu weaker than collision-resistance for proving the security of the scheme.

bart.preneel(AT)esat.kuleuven.be

Introduction Two parties communicating across an insecure channel need a method by which any attempt to modify the information sent by one to the other, or fake its origin, is detected. Most commonly such a mechanism is based on a shared key between the parties, and in this setting is usually called a MAC, or Message Authentication Code. (Other terms include Integrity Check Value or Cryptographic Checksum). The sender appends to the data D an authentication tag computed as a function of the data and the shared key. At reception, the receiver recomputes the authentication tag on the received message using the shared key, and accepts the data as valid only if this value matches the tag attached to the received message. The most common approach is to construct MACs from block ciphers like DES. Of such constructions Department of Computer Science & Engineering, Mail Code 0114, University of California at San Diego, 9500 Gilman Driv

This paper initiates a study of accountable certificate management methods, necessary to support long-term authenticity of digital documents. Our main contribution is a model for accountable certificate management, where clients receive attestations confirming inclusion/removal of their certificates from the database of valid certificates. We explain why accountability depends on the inability of the third parties to create contradictory attestations. After that we define an undeniable attester as a primitive that provides efficient attestation creation, publishing and verification, so that it is intractable to create contradictory attestations. We introduce authenticated search trees and build an efficient undeniable attester upon them. The proposed system is the first accountable long-term certificate management system. Moreover, authenticated search trees can be used in many security-critical applications instead of the (sorted) hash trees to reduce trust in the authorities, without decrease in efficiency. Therefore, the undeniable attester promises looks like a very useful cryptographic primitive with a wide range of applications.

Abstract. This paper reconsiders the established Merkle-Damg˚ard design principle for iterated hash functions. The internal state size w of an iterated n-bit hash function is treated as a security parameter of its own right. In a formal model, we show that increasing w quantifiably improves security against certain attacks, even if the compression function fails to be collision resistant. We propose the wide-pipe hash, internally using a w-bit compression function, and the double-pipe hash, with w = 2n and an n-bit compression function used twice in parallel.

Cryptographic primitives are usually based on a network with some gates. In [SV94], it is claimed that all gates should be multipermutations. In this paper, we investigate a few combinatorial properties of multipermutations. We argue that gates which fail to be multipermutations can open the way to unsuspected attacks. We illustrate this statement with two examples. Firstly, we show how to construct collisions to MD4 restricted to its first two rounds. This allows to forge digests close to each other using the full compression function of MD4. Secondly, we show that some generalizations of SAFER are subject to attack faster than exhaustive search in 6:1% cases. This attack can be implemented if we decrease the number of rounds from 6 to 4. In [SV94], multipermutations are introduced as formalization of perfect diffusion. The aim of this paper is to show that the concept of multipermutation is a basic tool in the design of dedicated cryptographic functions, as functions that do not rea...