Data Protection and Security

I

Secret Key Cryptography

I.II

Hash Functions

Recent Attacks on Hash Functions

Today, more than 90% of hash function applications use either MD5 or SHA-1, which has 128-bits and 160-bits of hash outputs respectively. Since last year, no real security vulnerability has been discovered in them hence they were considered to be secure (the birthday attack for MD5 requires 2⁶⁴ operations which barely passes the threshold considering today’s computational power). This situation has been changed by the discovery of new attacks by Chinese cryptanalysts in 2004. These attacks reduce significantly the amount of work required to find collisions (2³⁹ operations for MD5 and 2⁶⁹ operations for SHA-1 as of May 2005).

Regarding pre-image attacks and second pre-image attacks, no flaw has been found yet. Nevertheless, some starts thinking to have a new hash function standard, possibly after a process similar to the successful one used to choose AES.