[OT] looking for a algorithm

[Martin Tournoij]

On Sun, May 25, 2008 at 04:10:01PM -0400, Aryeh M. Friedman wrote:
> Lets say I have a string of n bits that needs to be filled by repeatedly 
> applying some function on k strings of m bits where |m|<|n|.   Assuming 
> that m(i) is a random string and n needs to also be random what is the best 
> way to do this.  Note it is possible that k*|m|>|n|.   What I have been 
> thinking so far is:
> 
> ~    Let m' be the average length of m       // this is pre-computable
> ~    Let n be all 0's
> 
> ~    for i=0 --> k
> ~       pos=m'*i
> 
> ~       xor string k[i] onto n starting at pos   // wrap around if needed
> 
> ~    While this is simple I wonder if it can be attacked (determine what 
> k[i]) if k*|m|>|n| (it is trivial to attack if k*|m|<=|n|).   Also is there 
> some way to make attacking hard if k*|m|<=|n|?
> 
> ~    Ideas?

So you want us to do your homework...?

-- 
Martin Tournoij
carpetsmoker at rwxrwxrwx.net
http://www.daemonforums.org

Information is the inverse of entropy.