olemus
bittide arvu vähendav P-teisendus
= a permutation box (P-box) with n inputs and m outputs where m < n
https://image.slidesharecdn.com/modernblockcipher-170817223658/95/modern-block-cipher-17-1024.jpg
http://images.slideplayer.com/35/10395470/slides/slide_15.jpg
http://slideplayer.com/slide/6826820/23/images/24/Compression/Expansion+P-Boxes.jpg

vt ka
- neutraalne P-teisendus
- paisutav P-teisendus