vigenere_diy.js

/**
 * Created by rhett on 7/9/15.
 */

var encrypt = function (message, pass, shift) {

  var alpha = shiftAlpha(shift);

  message = message.toUpperCase().split('');
  pass = pass.toUpperCase().replace(/\s/g, '').split('').map(function (i) {
    return alpha.indexOf(i);
  });

  var aLen = alpha.length;

  var out = '';
  for (var i = 0; i < message.length; i++) {
    var Ma     = message[i],
        Kb     = pass[i % pass.length],

        MaNum  = alpha.indexOf(Ma),

        Ca     = (aLen + MaNum + Kb) % aLen;

    out += alpha[Ca];
  }

  return out;

};
var decrypt = function (code, pass, shift) {

  var alpha = shiftAlpha(shift);

  code = code.toUpperCase().split('');
  pass = pass.toUpperCase().split('').map(function (i) {
    return alpha.indexOf(i);
  });

  var aLen = alpha.length;

  var out = '';
  for (var i = 0; i < code.length; i++) {
    var Ca    = code[i],
        Kb    = pass[i % pass.length],

        CaNum = alpha.indexOf(Ca),

        Ma    = (aLen + CaNum - Kb) % aLen;

    out += alpha[Ma];
  }

  return out;

};
var extrapPass = function (msg, code, shift) {

  var alpha = shiftAlpha(shift);

  msg = msg.toUpperCase().split('');
  code = code.toUpperCase().split('');

  var aLen = alpha.length;

  var out = '';
  for (var i = 0; i < code.length; i++) {
    var Ma    = msg[i],
        Ca    = code[i],

        MaNum = alpha.indexOf(Ma),
        CaNum = alpha.indexOf(Ca),

        Ka    = (aLen + CaNum - MaNum) % aLen;

    out += alpha[Ka];
  }

  return out;

};

var shiftAlpha = function(shift){
  var alpha = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ';

  if (shift) {
    return (shift.toUpperCase() + alpha)
      .split('')
      .reduce(function(last, next){
        if (last.indexOf(next) === -1) {
          last.push(next);
        }
        return last;
      }, [])
      .join('');
  } else {
    return alpha;
  }
};


var msg    = 'abcdzz', pass = 'zabbzz', key = 'booth',
    code   = encrypt(msg, pass, key),
    retMsg = decrypt(code, pass, key),
    retPass = extrapPass(msg, code, key);

console.log(pass, msg, key, code, retMsg, retPass);


//console.log(extrapPass('comanche', 'EWTGQEPA', 'booth'));
console.log(decrypt('EWTGQEPA NIPZH', 'booth', 'booth'));


//console.log(shiftAlpha(''));
//console.log(shiftAlpha('booth'));