Generalization of two-square or double Playfair to four-square Playfair
From
Mok-Kong Shen@21:1/5 to
All on Thu Nov 16 23:02:21 2017
Playfair has been generalized to two-square Plafair. We further generalize
it to four-square Playfair, consisting of four distinct Playfairs of the
same arbitralily size forming a large rectangle. We shall employ the
Playfair rule as given in H. F. Gaines, Cryptanalysis, p.200. Thus the plaintext pair will be located in the quadrants froming a diagonal from
NW to SE and the ciphertext pair will be located in the quadrants forming
a diagonal from NE to SW.
Recommendations:
1. To fill an example simple Plyfair of 5*5, take 25 characters from a
natural language sentence and determine a sequence 1, 2, ... 25 as used
to choose the columns for columar transpostion (Gaines, p.37 fig.29). Use
this sequence to choose the 25 alphabetical characters to fill the rows of
the Playfair square.
2. To increase the complexity for the adversary, it can be advanatageous
to combine this cipher with a transposition, forming a cascade, e.g.
TPTPT. The transposition matrix could even contain black holes similar to
one invented in WWII by filling a matrix with a natural language sentence
and blacking positions where certain alphabetical characters stand to form
a transposition matrix with holes.
M. K. Shen
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