js加密字符串

/*
 * 字符串加密
 * 用javascript对字符串进行加密，应用于参数传递等。
 * 默认加密密钥为kb1234，使用者可自定义修改。
 * 注意加密密钥应和解密密钥相同。
 * 算法来自于互联网
 * 使用方法：
 * 加密
 * var code = kbt.encrypt('我爱北京天安门');
 * alert(code);
 * 解密
 * var str =  kbt.decrypt(code);
 * alert(str);
*/
var kbt = (function () {
    var that = {};
    
    function encrypt(str, pwd) {
        if(str == '') {
            return '';
        }
        str = encodeURIComponent(str);
        if(!pwd || pwd == '') {
            pwd = 'kb1234';
        }
        pwd = encodeURIComponent(pwd);   
        if(pwd == '' || pwd.length <= 0) {
            return '';
        }
        var prand = '';
        for(var i = 0, len = pwd.length; i < len; i += 1) {
            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) {
            return '';
        }
        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 encChr = '';
        var encStr = '';
        for(var i = 0, len = str.length; i < len; i += 1) {
            encChr = parseInt(str.charCodeAt(i) ^ Math.floor((prand / modu) * 255));
            if(encChr < 16) {
                encStr += '0' + encChr.toString(16);
            }else{
                encStr += encChr.toString(16);
            }
            prand = (mult * prand + incr) % modu;
        }   
        salt = salt.toString(16);
        while(salt.length < 8) {
            salt = "0" + salt;
        }
        encStr += salt;
        return encStr;
    }

    function decrypt(str, pwd) {
        if(str == ''){
            return '';
        }
        if(!pwd || pwd == ''){
            pwd = 'kb1234';
        }
        pwd = encodeURIComponent(pwd);
        if(str == undefined || str.length < 8) {
            return '';
        }
        if(pwd == undefined || pwd.length <= 0) {
            return '';
        }
        var prand = '';
        for(var i = 0, len = pwd.length; i < len; i += 1) {
            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.round(pwd.length / 2);
        var modu = Math.pow(2, 31) - 1;
        var salt = parseInt(str.substring(str.length - 8, str.length), 16);
        str = str.substring(0, str.length - 8);
        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 encChr = '';
        var encStr = '';
        for(var i = 0, len = str.length; i < len; i += 2) {
            encChr = parseInt(parseInt(str.substring(i, i + 2), 16) ^ Math.floor((prand / modu) * 255));   
            encStr += String.fromCharCode(encChr);   
            prand = (mult * prand + incr) % modu;   
        }
        return decodeURIComponent(encStr);
    }

    that.encrypt = encrypt;
    that.decrypt = decrypt;
    return that;
})();