From: Berzerk <berzerk@xmission.xmission.com>
Date: Sat, 16 Jul 94 16:35:51 PDT
Subject: Re: Hashed hash
In-Reply-To: <Pine.3.89.9407161315.B9512-0100000@Tux.Music.ASU.Edu>
Message-ID: <Pine.3.89.9407161720.A18856-0100000@xmission>
MIME-Version: 1.0
Content-Type: text/plain




On Sat, 16 Jul 1994, Ben Goren wrote:
> So, my question: for any of the popular hash algorithms H(m), is it known if 
> there is or is not an algorithm I(m) such that I(m)=H(H(m))? Are the hash 
> algorithms groups or not?
I too would be interested in this, but would also wory about the hash 
functions "converging" to one value.  Unless the function G(i) is one on 
one, and not a group, this not good.  [G(i): G=H(m;i) i=H(m)] You could 
loose information in in the G phase of hashing, and shoot yourself in the 
foot.  What is wrong with the folowing two stratigies.:

1)
let I(key,block) be Idea(key, block)
    N be the number of iterations.
 
and Si be a non-strong, simple sequence, like from a LCG.
do I(S1,I(s2,i(s3,..........,i(sN,m);
for however many times, then hash it.

2) 
use a salt value, n. with n%N not equal to 0;
do 
 {
  m=i(s1,previous m)
 and 
  n=i(n,previous n)
  
  
 } untill (n%N=0)

Number 2 has the added bonus of working with true random numbers for n, 
so if you wanted to inclose the value of n in some encryption you have no 
plaintext.

If you keep this to 8 bits or so, you could use feal-4 instead of idea:-)

I asked a similar question about hash functions and have recieved no 
replies.

Roger.