Javascript加密解密

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//str 是想加密的字符串
//pwd 是key
function encrypt(str, 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.  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;
}


function decrypt(str, 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 enc_str;
}