[..] > How about some websites for starters? (or any other > interesting challenges for that matter... I took a liking to last one) http://www.tcs.hut.fi/~helger/crypto/link/block/cryptanalysis.html http://my.genie.co.uk/dkabambe/mathbook1.html http://www.fas.org/irp/doddir/army/fm34-40-2/ HTH Regards Chris Marsh