Re: Reverse Hash Function

*To*: mathgroup at smc.vnet.net*Subject*: [mg52909] Re: Reverse Hash Function*From*: David Bailey <dave at Remove_Thisdbailey.co.uk>*Date*: Thu, 16 Dec 2004 03:41:17 -0500 (EST)*References*: <cpp1u5$b01$1@smc.vnet.net>*Sender*: owner-wri-mathgroup at wolfram.com

Linda Pan wrote: > Dear experts, > > I met a problem, and I don't have experience to solve it. Thus, please give > me a help. > > > > My question is: > > > > I have a hash function: h(). > > I have a plain text: A > > > > So I can get a hash value B = h(A) > > > > Suppose that I have a reverse hash function: h'() > > > > Then I can get a fade plain text A'= h'(B), probably A' is not equal to A, > but it doesn't matter! > > > > I want to ask: Is it possible to build a reverse hash function h'() so that > h(h'(B)) is equal to B? > > > > I do appreciate if you could answer me or send me a hint. > > > > Merry Christmas! > > > > P. L. > > > Hi, Think of the number of bits in your original text and in the resultant hash value. Normally a lot of information is lost in a hash function - so you can't reverse the process. Algorithms that use hash functions always make provision for the possibility that several things hash to the same number. David Bailey dbaileyconsultancy.co.uk