Xamarin.android- how to make encryption/decryption of images faster

Question

I want users to select images/videos from gallery and secure their images within my app. for that, I encrypt those images. Encryption over images works correctly(I think so !).

Answer 1

I didn't find any post/blog related to encrypting decrypting file

You can use CipherOutputStream and CipherInputStream to achieve it.

Here is my test demo, you can try it, and you need push a video file named videoplayback.mp4 into your phone which path is /storage/sdcard/Movies, so you can test my code directly.

using Android.App;
using Android.Widget;
using Android.OS;
using Javax.Crypto.Spec;
using Java.Lang;
using Java.IO;
using Javax.Crypto;
using System.Text;

namespace EncryTest
{
    [Activity(Label = "EncryTest", MainLauncher = true)]
    public class MainActivity : Activity
    {
        long stopTime, startTime;
        private string sKey = "0123456789abcdef";//key，
        private string ivParameter = "1020304050607080";
        protected override void OnCreate(Bundle savedInstanceState)
        {
            base.OnCreate(savedInstanceState);

            // Set our view from the "main" layout resource
            SetContentView(Resource.Layout.Main);

            encrypt("videoplayback.mp4");
            decrypt("videoplayback.mp4");
        }

        public void encrypt(string filename)
        {

            // Here you read the cleartext.
            try
            {
                File extStore = Environment.GetExternalStoragePublicDirectory(Environment.DirectoryMovies);
                startTime = System.DateTime.Now.Millisecond;
                Android.Util.Log.Error("Encryption Started", extStore + "/" + filename);

                // This stream write the encrypted text. This stream will be wrapped by
                // another stream.
                createFile(filename, extStore);
                System.IO.FileStream fs=System.IO.File.OpenRead(extStore + "/" + filename);
                FileOutputStream fos = new FileOutputStream(extStore + "/" + filename + ".aes", false);

                // Length is 16 byte
                Cipher cipher = Cipher.GetInstance("AES/CBC/PKCS5Padding");
                byte[] raw = System.Text.Encoding.Default.GetBytes(sKey);
                SecretKeySpec skeySpec = new SecretKeySpec(raw, "AES");
                IvParameterSpec iv = new IvParameterSpec(System.Text.Encoding.Default.GetBytes(ivParameter));//
                cipher.Init(CipherMode.EncryptMode, skeySpec, iv);

                // Wrap the output stream
                CipherInputStream cis = new CipherInputStream(fs, cipher);
                // Write bytes
                int b;
                byte[] d = new byte[1024 * 1024];
                while ((b = cis.Read(d)) != -1)
                {
                    fos.Write(d, 0, b);
                }
                // Flush and close streams.
                fos.Flush();
                fos.Close();
                cis.Close();
                stopTime = System.DateTime.Now.Millisecond;
                Android.Util.Log.Error("Encryption Ended", extStore + "/5mbtest/" + filename + ".aes");
                Android.Util.Log.Error("Time Elapsed", ((stopTime - startTime) / 1000.0) + "");
            }
            catch (Exception e)
            {
                Android.Util.Log.Error("lv",e.Message);
            }

        }


        private void createFile(string filename, File extStore)
        {
            File file = new File(extStore + "/" + filename + ".aes");

            if (filename.IndexOf(".") != -1)
            {
                try
                {
                    file.CreateNewFile();
                }
                catch (IOException e)
                {
                    // TODO Auto-generated catch block
                    Android.Util.Log.Error("lv",e.Message);
                }
                Android.Util.Log.Error("lv","file created");
            }
            else
            {
                file.Mkdir();
                Android.Util.Log.Error("lv","folder created");
            }

            file.Mkdirs();
        }
        public void decrypt(string filename)
        {
            try
            {

                File extStore = Environment.GetExternalStoragePublicDirectory(Environment.DirectoryMovies);
                Android.Util.Log.Error("Decryption Started", extStore + "");
                FileInputStream fis = new FileInputStream(extStore + "/" + filename + ".aes");

                createFile(filename, extStore);
                FileOutputStream fos = new FileOutputStream(extStore + "/" + "decrypted" + filename, false);
                System.IO.FileStream fs = System.IO.File.OpenWrite(extStore + "/" + "decrypted" + filename);
                // Create cipher

                Cipher cipher = Cipher.GetInstance("AES/CBC/PKCS5Padding");
                byte[] raw = System.Text.Encoding.Default.GetBytes(sKey);
                SecretKeySpec skeySpec = new SecretKeySpec(raw, "AES");
                IvParameterSpec iv = new IvParameterSpec(System.Text.Encoding.Default.GetBytes(ivParameter));//
                cipher.Init(CipherMode.DecryptMode, skeySpec, iv);

                startTime = System.DateTime.Now.Millisecond;
                CipherOutputStream cos = new CipherOutputStream(fs, cipher);
                int b;
                byte[] d = new byte[1024 * 1024];
                while ((b = fis.Read(d)) != -1)
                {
                    cos.Write(d, 0, b);
                }

                stopTime = System.DateTime.Now.Millisecond;

                Android.Util.Log.Error("Decryption Ended", extStore + "/" + "decrypted" + filename);
                Android.Util.Log.Error("Time Elapsed", ((stopTime - startTime) / 1000.0) + "");

                cos.Flush();
                cos.Close();
                fis.Close();
            }
            catch (Exception e)
            {
                Android.Util.Log.Error("lv", e.Message);
            }
        }
    }
}

The video just for test, you can get the video file from another path, just a little change will be good.

About the path /storage/sdcard/Movies, I think a picture will be better to understand it