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function vigenere(mode, key, msg) {
let alph = "abcdefghijklmnopqrstuvwxyz";
let q = msg.length / key.length;
while (q > 0) {
key += key;
q--;
}
while (key.length > msg.length) {
key = key.substr(0,key.length-1);
}
let msg_letters = msg.split('');
let key_letters = key.split('');
let rots = [];
for (let i = 0; i < key_letters.length; i++) {
rots.push(alph.indexOf(i));
}
let ans_letters = [];
for (let i = 0; i < msg_letters.length; i++) {
if (!msg_letters[i].match(/[a-z]/)) {
ans_letters.push(msg_letters[i]);
continue;
}
let v = alph.indexOf(msg_letters[i]);
let x = 0;
if (mode == 0)
x = (v + rots[i]) % 26;
else
x = (v - rots[i]) % 26;
let letter = alph.substr(x,1);
ans_letters.push(letter);
}
return ans_letters.join('');
}
let msg = "hello world";
let key = "test";
let enc = vigenere(0, key, msg);
let dec = vigenere(1, key, enc);
console.log(enc);
console.log(dec);
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