js 加密方法Encrypt

function Encrypt(str, pwd) {
        if (str == "") return "";
        str = escape(str);
        if (!pwd || pwd == "") {
            var pwd = "1234";
        }
        pwd = escape(pwd);
        if (pwd == null || pwd.length <= 0) {
            alert("Please enter a password with which to encrypt the message.");
            return null;
        }
        var prand = "";
        for (var I = 0; I < pwd.length; I++) {
            prand += pwd.charCodeAt(I).toString();
        }
        var sPos = Math.floor(prand.length / 5);
        var mult = parseInt(prand.charAt(sPos) + prand.charAt(sPos * 2) + prand.charAt(sPos * 3) + prand.charAt(sPos * 4) + prand.charAt(sPos * 5));
        var incr = Math.ceil(pwd.length / 2);
        var modu = Math.pow(2, 31) - 1;
        if (mult < 2) {
            alert("Algorithm cannot find a suitable hash. Please choose a different password. /n Possible considerations are to choose a more complex or longer password.");
            return null;
        }
        var salt = Math.round(Math.random() * 1000000000) % 100000000;
        prand += salt;
        while (prand.length > 10) {
            prand = (parseInt(prand.substring(0, 10)) + parseInt(prand.substring(10, prand.length))).toString();
        }
        prand = (mult * prand + incr) % modu;
        var enc_chr = "";
        var enc_str = "";
        for (var I = 0; I < str.length; I++) {
            enc_chr = parseInt(str.charCodeAt(I) ^ Math.floor((prand / modu) * 255));
            if (enc_chr < 16) {
                enc_str += "0" + enc_chr.toString(16);
            } else
                enc_str += enc_chr.toString(16);
            prand = (mult * prand + incr) % modu;
        }
        salt = salt.toString(16);
        while (salt.length < 8) salt = "0" + salt;
        enc_str += salt;
        return enc_str;
    }