采用密码加密的javascript字符串加密、解密程序

本程序原取自网络，在加密字符串时可以采用设置密码，密文必须使用相同密码采用解密出明文，否则返回的将会是乱码。
原文仅可以加密解密E文，密码也只能采用E文，偶稍加修改后，可以加解密中文，密码也可以采用中文密码，比较实用。
如果不设置密码，则采用默认密码"1234"进行加解密。

以下是修改后的程序代码：

<SCRIPT LANGUAGE="JavaScript">
<!-- Begin

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. \nPossible 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;
}

function Decrypt(str, pwd) {
    if(str=="")return "";
    if(!pwd || pwd==""){ var pwd="1234"; }
    pwd = escape(pwd);
      if(str == null || str.length < 8) {
        alert("A salt value could not be extracted from the encrypted message because it's length is too short. The message cannot be decrypted.");
        return;
      }
      if(pwd == null || pwd.length <= 0) {
        alert("Please enter a password with which to decrypt the message.");
        return;
      }
      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.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 enc_chr = "";
      var enc_str = "";
    for(var I=0; I<str.length; I+=2) {
        enc_chr = parseInt(parseInt(str.substring(I, I+2), 16) ^ Math.floor((prand / modu) * 255));
        enc_str += String.fromCharCode(enc_chr);
        prand = (mult * prand + incr) % modu;
    }
    return unescape(enc_str);
}
//  End -->
</script>