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:
ALGOL 68
Note: This specimen retains the original C++ coding style.
<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>
- 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