This code implement the Vigenere cypher to solve EFF Puzzle (2014).

vigenere.js

/* 
  This is the implementation in JS of the Vigenere cypher to solve EFF puzzle:
  https://www.eff.org/deeplinks/2014/08/effs-defcon-22-t-shirt-puzzle-explained
  */
  
String.prototype.charOrdinalCodeAt = function(pos){
	/*
	This function returns this values:
	* -1 if the character at position pos is not a letter;
	* if the character at position pos is a letter it returns the positional value in alphabet, for lower case letter it returns its positional value + 26, for example:
	* s = "Aa+";
	* charOrdinalCodeAt(0) = 0
	* charOrdinalCodeAt(1) = 26
	* charOrdinalCodeAt(2) = -1
	*/
	let vc = this.charCodeAt(pos);
	if ((vc<65) || (vc>122) || ((vc>90) && (vc<96))) return -1;
	vc = vc -65;
	if (vc>25) vc = vc - 6;
	return vc;
}

String.prototype.onlyLetters = function(){
	/* This function remove all non letters from  a string */
		return this.replace(/[^\w]/g, '');
}

vigenere = function(phrase, keyword, state){
	let cypher = '';
	// keyword must contains only upper case letters A-Z
	keyword = keyword.onlyLetters().toUpperCase();
	let j = 0; // counts character to use in keyword
	for (i=0; i<phrase.length; i++){
		val = phrase.charOrdinalCodeAt(i);
		if (val<0) enci = phrase[i]; // when character is not a letter simply return it
		else {
			enci = (((val % 26) + state*keyword.charOrdinalCodeAt(j)) + 26) % 26;
			enci = String.fromCharCode(enci+65);
			if (val>25) enci = enci.toLowerCase();
			j = (j + 1) % keyword.length;
			
		}
		cypher+=enci;
	}
	return cypher;
}
vigenereEnc=function(phrase, keyword){
return vigenere(phrase, keyword,1);
}

vigenereDec = function(phrase, keyword){
	return vigenere(phrase,  keyword, -1);
}

vigenere2 = function(phrase, keyword, state){
	let cypher = '';
	keyword = normalizeKeyword(phrase, keyword);
	let j = 0;
	for (i=0; i<phrase.length; i++){
		val = valLetter(phrase[i])
		if (val<0) enci = phrase[i];
		else {
			enci = (((val) + state*valLetter(keyword[j]))) % 52;
			if (enci < 0) enci+=52;
			enci = String.fromCharCode(enci+65);
			if (val>25) enci = enci.toLowerCase();
			j+=1 %keyword.length;
		}
		cypher+=enci;
	}
	return cypher;
}


s = "aA-";



msg = "[Iikcggu] Gvdw ag etxlku | [Ptjhafvmkx] rqgrva(cgvs urlaiaixcm Asiixl) | [Gwhusu] akksdx bzqaymoukh(gsyi, Jnsrgo) | [Rmtm] mwllzg(ihrl.qv_e? Wkivav)";
kw = "Everyone has something to hide";
alert(vigenereDec(msg,kw));

/* 
	* To test the encryption function I use the example on the english Wikipedia page:
	* http://en.wikipedia.org/wiki/Vigen%C3%A8re_cipher

msg = "ATTACKATDAWN";
kw = "lemon";
alert(vigenereEnc(msg, kw));
*/