[OT] looking for a algorithm

[Aryeh M. Friedman]

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

Martin Tournoij wrote:
| 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...?
|
If this was homework I would just use the above and take the b or what 
ever I would get on it but I need this for something else where any 
attack is not good.
-----BEGIN PGP SIGNATURE-----
Version: GnuPG v2.0.9 (FreeBSD)
Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org

iEYEARECAAYFAkg50QAACgkQk8GFzCrQm4BA2ACcC3s3JmVzqKwFDi+l1TtwsKXe
e1QAoMTBCmZi0rQueLkrGMJrzjVggWGR
=1954
-----END PGP SIGNATURE-----