Partial encryption of a binary file

Question

Can users provide me some steps in how to encrypt part of a binary file?

Here I have this code snippet below:

      private void Encrypt_Region_Button_Click(object sender, EventArgs e)
        {
            try
            {
                string FileName = @"C:\Users\...\Documents\Binary Image 001.img";

                MessageBox.Show("Encrypting " + FileName);

                // Encrypt the file.
                AddEncryption(FileName);

                MessageBox.Show("Done");

            }
            catch (Exception)
            {
                MessageBox.Show("Unable to encrypt file.");
            }

        }

What I want to do now, but I don't know how to perform this is to encrypt part of a binary file.
Can users provide me step by step?

Answer

I have improved my source code snippet.
See if any user can improve this one below.
private void Begin_Encryption_Button_Click(object sender, EventArgs e)
{

            try
            {
                File_For_Reading = File_Name_For_Reading_Text_Box.Text;
                File_For_Writing = File_Name_For_Writing_Text_Box.Text;
                Encrypt_Beginning_Point = int.Parse(Beginning_Part_of_Encryption_Text_Box.Text);
                Encrypt_End_Point = int.Parse(Ending_Part_of_Encryption_Text_Box.Text);

                using (RijndaelManaged aes = new RijndaelManaged())
                {
                    byte[] key = ASCIIEncoding.UTF8.GetBytes(skey);
                    byte[] IV = ASCIIEncoding.UTF8.GetBytes(skey);

                    using (FileStream xCrypt = new FileStream(File_For_Writing, FileMode.Create))
                    {
                        using (ICryptoTransform encryptor = aes.CreateEncryptor(key, IV))
                        {
                            using (CryptoStream cX = new CryptoStream(xCrypt, encryptor, CryptoStreamMode.Write))
                            {
                                using (FileStream XIn = new FileStream(File_For_Reading, FileMode.Open))
                                {
                                    int data;
                                    while (((data = XIn.ReadByte()) >=Encrypt_Beginning_Point) && (data = XIn.ReadByte()) <= Encrypt_End_Point)
                                    { 
                                        cX.WriteByte((byte)data);
                                        MessageBox.Show("Success! Part of file has been encrypted.");
                                    }
                                }
                            }
                        }
                    }
                }
            }
            catch (Exception)
            {
                MessageBox.Show("Failed to encrypt file.");

            }
        }

Answer

Hi John-1477,
You can initialize a buffer and will be processing the file in chunks.

using (FileStream XIn = new FileStream(File_For_Reading, FileMode.Open))  
{  
        int bufferLen = Encrypt_End_Point - Encrypt_Beginning_Point + 1;   
        byte[] buffer = new byte[bufferLen];   
        int bytesRead;   
  
        do {   
            // read a chunk of data from the  file   
            bytesRead = XIn.Read(buffer, 0, bufferLen);   
  
            // Decrypt it   
            cX.Write(buffer, 0, bytesRead);   
  
        } while(bytesRead != 0);   
}

Best Regards,
Daniel Zhang

If the response is helpful, please click "Accept Answer" and upvote it.

Note: Please follow the steps in our documentation to enable e-mail notifications if you want to receive the related email notification for this thread.

Partial encryption of a binary file

2 answers