SHA-2

About: SHA-2 is a research topic. Over the lifetime, 2017 publications have been published within this topic receiving 56431 citations. The topic is also known as: SHA-2 & SHA2.

Keying Hash Functions for Message Authentication

Abstract: The use of cryptographic hash functions like MD5 or SHA-1 for message authentication has become a standard approach in many applications, particularly Internet security protocols. Though very easy to implement, these mechanisms are usually based on ad hoc techniques that lack a sound security analysis. We present new, simple, and practical constructions of message authentication schemes based on a cryptographic hash function. Our schemes, NMAC and HMAC, are proven to be secure as long as the underlying hash function has some reasonable cryptographic strengths. Moreover we show, in a quantitative way, that the schemes retain almost all the security of the underlying hash function. The performance of our schemes is essentially that of the underlying hash function. Moreover they use the hash function (or its compression function) as a black box, so that widely available library code or hardwair can be used to implement them in a simple way, and replaceability of the underlying hash function is easily supported.

Finding collisions in the full SHA-1

Abstract: In this paper, we present new collision search attacks on the hash function SHA-1. We show that collisions of SHA-1 can be found with complexity less than 269 hash operations. This is the first attack on the full 80-step SHA-1 with complexity less than the 280 theoretical bound.

How to break MD5 and other hash functions

Abstract: MD5 is one of the most widely used cryptographic hash functions nowadays. It was designed in 1992 as an improvement of MD4, and its security was widely studied since then by several authors. The best known result so far was a semi free-start collision, in which the initial value of the hash function is replaced by a non-standard value, which is the result of the attack. In this paper we present a new powerful attack on MD5 which allows us to find collisions efficiently. We used this attack to find collisions of MD5 in about 15 minutes up to an hour computation time. The attack is a differential attack, which unlike most differential attacks, does not use the exclusive-or as a measure of difference, but instead uses modular integer subtraction as the measure. We call this kind of differential a modular differential. An application of this attack to MD4 can find a collision in less than a fraction of a second. This attack is also applicable to other hash functions, such as RIPEMD and HAVAL.

A design principle for hash functions

Abstract: We show that if there exists a computationally collision free function f from m bits to t bits where m > t, then there exists a computationally collision free function h mapping messages of arbitrary polynomial lengths to t-bit strings.Let n be the length of the message, h can be constructed either such that it can be evaluated in time linear in n using 1 processor, or such that it takes time O(log(n)) using O(n) processors, counting evaluations of f as one step. Finally, for any constant k and large n, a speedup by a factor of k over the first construction is available using k processors.Apart from suggesting a generally sound design principle for hash functions, our results give a unified view of several apparently unrelated constructions of hash functions proposed earlier. It also suggests changes to other proposed constructions to make a proof of security potentially easier.We give three concrete examples of constructions, based on modular squaring, on Wolfram's pseudoranddom bit generator [Wo], and on the knapsack problem.

Universal one-way hash functions and their cryptographic applications

Abstract: We define a Universal One-Way Hash Function family, a new primitive which enables the compression of elements in the function domain. The main property of this primitive is that given an element x. We prove constructively that universal one-way hash functions exist if any 1-1 one-way functions exist.Among the various applications of the primitive is a One-Way based Secure Digital Signature Scheme, a system which is based on the existence of any 1-1 One-Way Functions and is secure against the most general attack known. Previously, all provably secure signature schemes were based on the stronger mathematical assumption that trapdoor one-way functions exist.