I understand what is happening and how the endpoint is computed but I'm still a bit unsure of where "SP" (Staring Point) came from. Are the starting points, randomly selected keys from the key-space n?

for example...


  • 1
    $\begingroup$ What reference are you pulling this terminology from? That context would be helpful. $\endgroup$
    – mikeazo
    Commented Apr 11, 2016 at 14:47
  • $\begingroup$ Sorry, I've included an example image. Alot of images that I find start with either S or SP for starting point. I'm just trying to figure out exactly what this is. $\endgroup$
    – ellefc
    Commented Apr 11, 2016 at 15:04

1 Answer 1


Given the diagram, yes they are randomly selected keys, $P$ is a fixed plaintext and the projection of the output to the keyspace gives you the next input as key to the cipher, thus creating a pseudorandom walk through the keyspace.


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