SHA-3 – The new hash standard

Die Hard

Article from ADMIN 13/2013

By Hanno Böck

NIST has chosen the Keccak algorithm as the new cryptographic hash standard but, in real life, many users are still waiting to move to its predecessor SHA-2.

Cryptographic hash functions are an important building block for secure communications on the internet. Many changes have occurred in recent years. MD5 and SHA-1, which have been in use for many years, turned out not to be as secure as originally thought. The Flame virus, which was discovered on many computers in the middle East in May last year, exploited an MD5 vulnerability to install itself via the Windows update service.

Following cryptographic breakthroughs, the National Institute for Standards and Technology (NIST) decided to launch a competition [1] for the development of a new hash standard. In October of 2012, the winner was chosen: the Keccak [2] algorithm, which was developed by a team of Belgian scientists. This is the second competition of this type: The symmetrical encryption algorithm AES, which is found in nearly every cryptographic application today, was chosen in 2003 in the course of a similar competition.

So, what do cryptographic hash functions do? To put it simply, they convert arbitrary input to fixed length output. The output is typically a hex number: for example, the MD5 hash of the word "Hello" is 8b1a9953c4611296a827abf8c47804d7. To be secure, a cryptographic hash function needs to fulfill two conditions:

Irreversible: It must be extremely difficult to find input that reproduces a given hash.
Collision resistant: It must be extremely difficult to find two inputs that generate the same output.

Cryptographic hash functions are used for many purposes, the most important being digital signatures. Signature methods such as RSA do not use the entire input, but only the hash of the input. But, hash functions are used in many other applications. For example, secure protocols such as SSL/TLS are complex constructs that use hash functions as building blocks for different

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