if ((cordova.platformId == "windows")) {
    var Cryptography = Windows.Security.Cryptography;
    //Encrypt the msg string
    function protectData(msg) {
        var provider = new Cryptography.DataProtection.DataProtectionProvider("LOCAL=user");
        var encoding = Cryptography.BinaryStringEncoding.utf8;
        var buffMsg = Cryptography.CryptographicBuffer.convertStringToBinary(msg, encoding);
        provider.protectAsync(buffMsg).done(function (buffData) {
            //the encryption has succeeded
            writeToFile(buffData);
        });
    }
    //decrypt the buffProtected buffer
    function unprotectData(buffProtected) {
        var provider = new Cryptography.DataProtection.DataProtectionProvider("LOCAL=user");
        var encoding = Cryptography.BinaryStringEncoding.utf8;
        // Decrypt the protected message specified on input.
        provider.unprotectAsync(buffProtected).then(function (data) {
            var stringMsg = Cryptography.CryptographicBuffer.convertBinaryToString(Windows.Security.Cryptography.BinaryStringEncoding.utf8, data);
            document.getElementById("divResult").innerText = stringMsg;
        }, function (error) {
            console.log(error);
        });
    }

    function writeToFile(buffProtected) {
        Windows.Storage.ApplicationData.current.localFolder.createFileAsync("test.txt", Windows.Storage.CreationCollisionOption.replaceExisting)
        .then(function (storageFile) {
            Windows.Storage.FileIO.writeBufferAsync(storageFile, buffProtected).done(function(){});
            }, function (error) {
                console.log(error);
            })
    }

    function readFromFile() {
    Windows.Storage.ApplicationData.current.localFolder.getFileAsync("test.txt").then(function (storageFile) {
        var abc = storageFile;
        Windows.Storage.FileIO.readBufferAsync(storageFile).then(function (buffData) {
            //decrypt the data
            unprotectData(buffData);
        });
        }, function (error) {
            console.log(error);
        });
    }


    document.getElementById("btnEncrypt").onclick = function () {
        var data = document.getElementById("txtData").value;
        protectData(data);
    }

    document.getElementById("btnDecrypt").onclick = function () {
        readFromFile(unprotectData)
    }
}

<input type="text" id="txtData" placeholder="ToProtected Data" />
<button id="btnEncrypt">Encrypt Data</button>
<button id="btnDecrypt">Decrypt Data</button>
<div id="divResult"></div>