Playfair cipher: Difference between revisions
→{{header|APL}}: Add implementation
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Encoded: BM OD ZB XD NA BE KU DM UI XM MO UV IF
Decoded: HI DE TH EG OL DI NT HE TR EX ES TU MP
</pre>
=={{header|APL}}==
{{works with|Dyalog APL}}
<lang apl>⍝⍝⍝⍝ Utility functions
⍝ convert to uppercase
UpCase ← { 1 ⎕C ⍵ }
⍝ remove non-letters
JustLetters ← { ⍵ /⍨ ⍵∊⎕A }
⍝ replace 'J's with 'I's
ReplaceJ ← { ('J' ⎕R 'I') ⍵ }
⍝ Insert an 'X' between repeated letters
SplitDouble ← { (' '⎕R'X') ⍵ \⍨ 1,~⍵=1⌽⍵ }
⍝ Append an 'X' if the message is not of even length
PadEven ← { ⍵,(2|≢⍵) ⍴ 'X' }
⍝ Split text up into letter pairs
Pairs ← { (1=2|⍳≢⍵) ⊂ ∊ ⍵ }
⍝ Group text into chunks of five letters
Groups ← { (1=5|⍳≢⍵) ⊂ ∊ ⍵ }
⍝ Shift within 1-5 based on left arg (0 for +1,1 for -1)
Shift ← { ⍺ ← 0 ⋄ 1+5|(⍺+1)⌷⍵,3+⍵ }
⍝⍝⍝⍝ Playfair implementation
⍝ All the things we have to do to the plaintext, chained together
PreparePlaintext ← { PadEven SplitDouble ReplaceJ JustLetters UpCase ∊ ⍵ }
⍝ Ditto for ciphertext
PrepareCiphertext ← { JustLetters UpCase ∊ ⍵ }
⍝ Create the grid from the key
PrepareKey ← { 5 5⍴ ∪ ReplaceJ (JustLetters UpCase ⍵),⎕A }
⍝ Encode or decode a single pair of letters
∇resultPair ← grid TransformPair args;mode;inPair;l;r;i1;j1;i2;j2
mode inPair ← args
l r ← inPair
i1 j1 ← ⊃⍸grid=l
i2 j2 ← ⊃⍸grid=r
:If i1=i2
j1 ← mode Shift j1
j2 ← mode Shift j2
:Else
:If j1=j2
i1 ← mode Shift i1
i2 ← mode Shift i2
:Else
j1 j2 ← j2 j1
:EndIf
:EndIf
resultPair ← grid[(i1 j1)(i2 j2)]
∇
⍝ Encode or decode an entire message
∇resultText ← grid TransformText args; mode; inText
mode inText ← args
resultText ← Groups ∊ { grid TransformPair mode ⍵ } ¨ Pairs inText
∇
⍝ Specific transforms for each direction including key and text preparation
∇cipher ← key EncodeText plain
cipher ← (PrepareKey key) TransformText 0 (PreparePlaintext plain)
∇
∇plain ← key DecodeText cipher
plain ← (PrepareKey key) TransformText 1 (PrepareCiphertext cipher)
∇
⍝ Demo
key ← 'Playfair example'
plain ← 'Hide the gold in the tree stump.'
⎕ ← cipher ← key EncodeText plain
⎕ ← key DecodeText cipher</lang>
{{Out}}<pre> ⎕ ← cipher ← key EncodeText plain
┌─────┬─────┬─────┬─────┬─────┬─┐
│BMODZ│BXDNA│BEKUD│MUIXM│MOUVI│F│
└─────┴─────┴─────┴─────┴─────┴─┘
</pre>
<pre> ⎕ ← key DecodeText cipher
┌─────┬─────┬─────┬─────┬─────┬─┐
│HIDET│HEGOL│DINTH│ETREX│ESTUM│P│
└─────┴─────┴─────┴─────┴─────┴─┘
</pre>
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