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SUMMARY:On inverting the VMPC one-way function - Kamil Kulesza\, Universit
 y of Cambridge
DTSTART:20060509T151500Z
DTEND:20060509T161500Z
UID:TALK4950@talks.cam.ac.uk
CONTACT:Stephen Lewis
DESCRIPTION:Informally speaking\, one-way functions are functions for whic
 h it is "easy" to compute their values from their arguments but it is "com
 putationally infeasible" to reverse them i.e. to find their arguments know
 ing their values. A rigorous definition of the terms "easy" and "computati
 onally infeasible" is necessary but would detract from the simple idea tha
 t is being conveyed. Existence of one-way functions is only conjectured an
 d closely connected with Cook's hypothesis. Roughly speaking\, if P is not
  equal NP such functions should exist. Apart from their theoretical import
 ance\, one-way functions are fundamental for complexity based cryptography
 . The problem is being attacked in many ways and there are several instanc
 es which are perceived to be good candidates\, for instance factorisation 
 or discrete logarithm. There are also practical reasons to search for new 
 candidates. We investigate the possibilities of inverting the VMPC one-way
  function\, which was proposed at Fast Software Encryption 2004. (VMPC sta
 nds for Variably Modified Permutation Composition). First\, we describe th
 e function using the language of permutation theory. Next\, easily inverti
 ble instances of VMPC are derived. We also show that no VMPC function is o
 ne-to-one. Implications of these results for cryptographic applications of
  VMPC conclude the presentation.
LOCATION:Lecture Theatre 2\, Computer Laboratory\, William Gates Building
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