Vigenère cipher

Vigenère cipher is a draft programming task. It is not yet considered ready to be promoted as a complete task, for reasons that should be found in its talk page.

Implement a Vigenère cypher, both encryption and decryption. The program should handle keys and text of unequal length, and should capitalize everything and discard non-alphabetic characters. (If your program handles non-alphabetic characters in another way, make a note of it.)

See also:

• Vigenère Cipher/Cryptanalysis

ALGOL 68

Translation of: C++

Note: This specimen retains the original C++ coding style.

Works with: ALGOL 68 version Revision 1 - no extensions to language used.

Works with: ALGOL 68G version Any - tested with release 1.18.0-9h.tiny.

Works with: ELLA ALGOL 68 version Any (with appropriate job cards) - tested with release 1.8-8d.

<lang algol68>STRING key := "";

PROC vigenere cipher = (REF STRING key)VOID: (

 FOR i FROM LWB key TO UPB key DO
   IF key[i] >= "A" AND key[i] <= "Z" THEN
     key +:= key[i] FI;
   IF key[i] >= "a" AND key[i] <= "z" THEN
     key +:= REPR(ABS key[i] + ABS"A" - ABS"a") FI
 OD

);

PROC encrypt = (STRING text)STRING: (

 STRING out := "";

 INT j := LWB text;
 FOR i FROM LWB text TO UPB text DO
   CHAR c := text[i];

   IF c >= "a" AND c <= "z" THEN
     c := REPR(ABS c + (ABS"A" - ABS"a")) FI;
   IF c >= "A" AND c <= "Z" THEN
     out +:= REPR((ABS c + ABS key[j] - 2*ABS"A") MOD 26 + ABS"A");
     j := j MOD UPB key + 1
   FI
 OD;

 out

);

PROC decrypt = (STRING text)STRING: (

 STRING out;

 INT j := LWB text;
 FOR i FROM LWB text TO UPB text DO
   CHAR c := text[i];

   IF c >= "a" AND c <= "z" THEN
     c := REPR(ABS c + (ABS"A" - ABS"a")) FI;
   IF c >= "A" AND c <= "Z" THEN
     out +:= REPR((ABS c - ABS key[j] + 26) MOD 26 + ABS"A");
     j := j MOD UPB key + 1
   FI
 OD;

 out

);

main: (

 vigenere cipher(key:="VIGENERECIPHER");

 STRING original := "Beware the Jabberwock, my son! The jaws that bite, the claws that catch!";
 STRING encrypted := encrypt(original);
 STRING decrypted := decrypt(encrypted);

 print((original, new line));
 print(("Encrypted: ", encrypted, new line));
 print(("Decrypted: ", decrypted, new line))

)</lang> Output:

Beware the Jabberwock, my son! The jaws that bite, the claws that catch!
Encrypted: WMCEEIKLGRPIFVMEUGXQPWQVIOIAVEYXUEKFKBTALVXTGAFXYEVKPAGY
Decrypted: BEWARETHEJABBERWOCKMYSONTHEJAWSTHATBITETHECLAWSTHATCATCH

C++

<lang cpp>#include <iostream>

1. include <string>

using namespace std;

class Vigenere { public:

 string key;

 Vigenere(string key)
 {
   for(int i = 0; i < key.size(); ++i)
   {
     if(key[i] >= 'A' && key[i] <= 'Z')
       this->key += key[i];
     else if(key[i] >= 'a' && key[i] <= 'z')
       this->key += key[i] + 'A' - 'a';
   }
 }

 string encrypt(string text)
 {
   string out;

   for(int i = 0, j = 0; i < text.length(); ++i)
   {
     char c = text[i];
     
     if(c >= 'a' && c <= 'z')
       c += 'A' - 'a';
     else if(c < 'A' || c > 'Z')
       continue;

     out += (c + key[j] - 2*'A') % 26 + 'A'; 
     j = (j + 1) % key.length();
   }

   return out;
 }

 string decrypt(string text)
 {
   string out;

   for(int i = 0, j = 0; i < text.length(); ++i)
   {
     char c = text[i];
     
     if(c >= 'a' && c <= 'z')
       c += 'A' - 'a';
     else if(c < 'A' || c > 'Z')
       continue;

     out += (c - key[j] + 26) % 26 + 'A'; 
     j = (j + 1) % key.length();
   }

   return out;
 }

};

int main() {

 Vigenere cipher("VIGENERECIPHER");

 string original = "Beware the Jabberwock, my son! The jaws that bite, the claws that catch!";
 string encrypted = cipher.encrypt(original);
 string decrypted = cipher.decrypt(encrypted);

 cout << original << endl;
 cout << "Encrypted: " << encrypted << endl;
 cout << "Decrypted: " << decrypted << endl;

}</lang>

Output:

Beware the Jabberwock, my son! The jaws that bite, the claws that catch!
Encrypted: WMCEEIKLGRPIFVMEUGXQPWQVIOIAVEYXUEKFKBTALVXTGAFXYEVKPAGY
Decrypted: BEWARETHEJABBERWOCKMYSONTHEJAWSTHATBITETHECLAWSTHATCATCH