Symetric Encryption

SymetricEncryption.js

function SymetricEncryption(chars) {

    var self = this;
    
    self.alphabet = chars || "qwertyuiopasdfghjklzxcvbnmQWERTYUIOPASDFGHJKLZXCVBNM1234567890!@#$%^&*()_+-=`~[]\\{}|;':\",./<>? ";

    function gc(pos) {
        pos = pos % self.alphabet.length;
        return self.alphabet[pos >= 0 ? pos : pos + self.alphabet.length];
    }

    function gp (char) {
        return self.alphabet.indexOf(char);
    }

    function a(s, p, e) {
        var o = "", i = 0;
        s.split('').forEach(function (char){
            var p1 = gp(char), p2 = gp(p[i++ % p.length]);
            o += e ? gc(p1 + p2) : gc(p1 - p2);
        });
        return o;
    }

    self.encrypt = function (text, password) {
        return a(text, password, true);
    };

    self.decrypt = function (text, password) {
        return a(text, password, false);
    };

}