Portax test

Here’s another function to help identify a specific cipher type, in this case Portax.

function Ptaxtest(S:string): integer;
var i,hi, lo : integer;
begin
hi :=0; lo := 0;
  for i :=1 to Length(S) do
     begin
     if S[i] in ['w','j','m','b'] then hi := hi+1;
     if S[i] in ['r','s','y','z'] then lo := lo+1;
     end;
     if lo=0 then lo:=1;
  Ptaxtest :=  Round(20*hi/lo);
end;

The letters w,j,m,b are more frequent in Portax ciphers because they tend to encipher the high-frequency plaintext letters on the same columns on the lower (sliding) part of the key slide. Similarly the second set of letters tend to be low-frequency. Computing the ratio of these two sets is a good indicator of a Portax.

4 thoughts on “Portax test”

  1. That’s an interesting idea, using the high and low frequency ratio. The Portax test I’ve used the most is the one by AAHJU in the MJ 2001 Cryptogram. In fact I don’t recall it ever being wrong. I did use the score of the AAHJU test as one of the inputs to my ID tests.

    Incidentially I tried my ID tests on the CE ciphers in the MA 2019 Cryptogram. Unfortunately there was no Portax cipher in the column. There were 22 ciphers where my tests could be applied (I don’t count nulls , baconians, and a few others). The random forest test did poorly getting the correct type on top only 9 times. The neural net collection on the Bionsgadgets page got 14 correct. My experimental neural net collection got 17 correct, but the experimental test takes a long time to run.

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