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Playfair cipher: Difference between revisions
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→{{header|REXX}}: added whitespace and changed some comments, made some statements easier to read, added literal constants for better reading.
m (→{{header|REXX}}: added whitespace and changed some comments, made some statements easier to read, added literal constants for better reading.) |
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=={{header|REXX}}==
Quite a bit of the REXX code deals with error checking, accepting arguments, and displaying the options used, and displaying input and output.
<br>Thanks to Walter Pachl, this program is now sensitive of using a suitable ''double character'' when '''X''' is present in the cipher key.▼
▲
<br>Also, more thanks are due to Walter Pachl for finding that the cipher key can't contain the OMIT character.
<br>(this is the ''possible text'' part of the REXX code).
<lang rexx>/*REXX program implements a PLAYFAIR cipher (encryption and decryption).
@abc= 'abcdefghijklmnopqrstuvwxyz'; @abcU= @abc /*literals for lower and upper ABC's.*/
parse arg omit key '(' text /*TEXT is the phrase to be used. */
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if omit=='' | omit==',' then omit= 'J' /*the "omitted" character string. */
if text='' then text= 'Hide the gold in the tree stump!!' /*default.*/
upper omit @abcU /*uppercase OMIT characters & alphabet.*/▼
@uchars= 'unique characters.' /*a literal used below in an error msg.*/
newKey = scrub(key, 1) /*scrub old cipher key ──► newKey */
newText= scrub(text ) /* " " text ──► newText */
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if length(omit)\==1 then call err 'OMIT letter must be only one letter.'
if \datatype(omit, 'M') then call err 'OMIT letter must be a Latin alphabet letter.'
▲upper omit @abcU /*uppercase OMIT characters & alphabet.*/
▲@cant= 'can''t contain the "OMIT" character: ' omit /*literal used in error text*/
if pos(omit, newText)\==0 then call err 'TEXT' @cant
if pos(omit, newKey) \==0 then call err 'cipher key' @cant
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xx= 'X' /*character used for double characters.*/
if omit==xx then xx= 'Q' /* " " " " " */
if length(newKey)<3 then call err 'cipher key is too short, must be ≥ 3' @uchars
fill= space( translate(fill, , newKey), 0) /*remove any cipher characters. */
grid= newKey || fill /*only first 25 characters are used. */
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padL= 14 + 2
call show 'cleansed', newText
#=
do row =1 for 5 /*build array of individual cells. */
do col=1 for 5; #= # + 1; @.row.col= substr(grid, #, 1)
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show: arg ,y; say; say right(arg(1) 'text: ',padL) digram(y); say pad space(y, 0); return
/*──────────────────────────────────────────────────────────────────────────────────────*/
.Playfair: arg T,encrypt; i= -1; if encrypt==1 then i= 1; $=
do k=1 while i==1; _= substr(T, k, 1); if _==' ' then leave
if _==substr(T, k+1, 1) then T= left(T, k) || Lxx || substr(T, k + 1)
end /*k*/
upper T
do j=1 by 2 to length(T); __= strip( substr(T, j, 2) )
if LR()==1 then __= __ || xx; call LR
select /*rule*/
when rowL==rowR then __= @@(rowL, colL+i)@@(rowR, colR+i)
when colL==colR then __= @@(rowL+i, colL )@@(rowR+i, colR)
otherwise __= @@(rowL, colR )@@(rowR, colL)
end /*select*/
$= $ || __
end /*j*/
return $
/*──────────────────────────────────────────────────────────────────────────────────────*/
digram: procedure;
return strip($)
/*──────────────────────────────────────────────────────────────────────────────────────*/
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$=; do j=1 for length(xxx); _= substr(xxx, j, 1)
if unique==1 then if pos(_, $)\==0 then iterate /*is unique?*/
if datatype(_, 'M') then $= $ ||
end /*j*/
return $</lang>
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