Vigenère cipher: Difference between revisions
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OSETH ENAME OFACT IONSO FTYOU NOWTH EFAIR OPHEL IANYM PHINT HYORI SONSB
EALLM YSINS REMEM BERED
</pre>
=={{header|Pascal}}==
<lang pascal>
// The Vigenere cipher in reasonably standard Pascal
// <no library functions: all conversions hand-coded>
PROGRAM Vigenere;
// get a letter's alphabetic position (A=0)
FUNCTION letternum(letter: CHAR): BYTE;
BEGIN
letternum := (ord(letter)-ord('A'));
END;
// convert a character to uppercase
FUNCTION uch(ch: CHAR): CHAR;
BEGIN
uch := ch;
IF ch IN ['a'..'z'] THEN
uch := chr(ord(ch) AND $5F);
END;
// convert a string to uppercase
FUNCTION ucase(str: STRING): STRING;
var i: byte;
BEGIN
ucase := '';
FOR i := 1 TO Length(str) DO
ucase := ucase + uch(str[i]);
END;
// construct a Vigenere-compatible string:
// uppercase; no spaces or punctuation.
FUNCTION vstr(pt: STRING): STRING;
VAR c: Cardinal;
s: STRING;
BEGIN
vstr:= '';
s := ucase(pt);
FOR c := 1 TO Length(s) DO BEGIN
IF s[c] IN ['A'..'Z'] THEN
vstr += s[c];
END;
END;
// construct a repeating Vigenere key
FUNCTION vkey(pt, key: STRING): STRING;
VAR c,n: Cardinal;
k : STRING;
BEGIN
k := vstr(key);
vkey := '';
FOR c := 1 TO Length(pt) DO BEGIN
n := c mod (Length(k));
IF n>0 THEN vkey += k[n] ELSE vkey += k[Length(k)];
END;
END;
// Vigenere encipher
FUNCTION enVig(pt,key:STRING): STRING;
VAR ct: STRING;
c,n : Cardinal;
BEGIN
ct := pt;
FOR c := 1 TO Length(pt) DO BEGIN
n := letternum(pt[c])+letternum(key[c]);
n := n mod 26;
ct[c]:=chr(ord('A')+n);
END;
enVig := ct;
END;
// Vigenere decipher
FUNCTION deVig(ct,key:STRING): STRING;
VAR pt : STRING;
c,n : INTEGER;
BEGIN
pt := ct;
FOR c := 1 TO Length(ct) DO BEGIN
n := letternum(ct[c])-letternum(key[c]);
IF n<0 THEN n:=26+n;
pt[c]:=chr(ord('A')+n);
END;
deVig := pt;
END;
VAR key: STRING = 'Vigenere cipher';
msg: STRING = 'Beware the Jabberwock! The jaws that bite, the claws that catch!';
vtx: STRING = '';
ctx: STRING = '';
ptx: STRING = '';
BEGIN
// make Vigenere-compatible
vtx := vstr(msg);
key := vkey(vtx,key);
// Vigenere encipher / decipher
ctx := enVig(vtx,key);
ptx := deVig(ctx,key);
// display results
Writeln('Message : ',msg);
Writeln('Plaintext : ',vtx);
Writeln('Key : ',key);
Writeln('Ciphertext : ',ctx);
Writeln('Plaintext : ',ptx);
END.
</lang>
Program output:
<pre>
Message : Beware the Jabberwock! The jaws that bite, the claws that catch!
Plaintext : BEWARETHEJABBERWOCKTHEJAWSTHATBITETHECLAWSTHATCATCH
Key : VIGENERECIPHERVIGENERECIPHERVIGENERECIPHERVIGENEREC
Ciphertext : WMCEEIKLGRPIFVMEUGXXYILILZXYVBHMGIKLGKAHAJOPGXPEKGJ
Plaintext : BEWARETHEJABBERWOCKTHEJAWSTHATBITETHECLAWSTHATCATCH
</pre>
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