Encrypting Files

The TEAgentFile class of the Pi Soft Java TEAgent package represents a file. It is used to encrypt, decrypt a file given the file path. The following sequence describes file encryption and decryption using this class.

1. Create a TEAgentFile object
2. Set the path of the file to be encrypted or decrypted, also set the path of the output file
3. Attach a connection
4. Encrypt or decrypt the file
5. Detach the connection

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Sample_Bonus_Crypt_Image.java

The following code sample illustrates how to evaluate a file and then encrypting and decrypting it.

import java.io.BufferedInputStream;
import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.util.Arrays;

import com.eruces.teagent.TEAgentConnection;
import com.eruces.teagent.TEAgentException;
import com.eruces.teagent.TECipher;
import com.eruces.teagent.TEKey;

public class Sample_Bonus_Crypt_Image {

    private static TEAgentConnection conn;
    private static byte[] ttag;
    
    private static byte[] readBMP(String strFile) {
        
        FileInputStream fis = null;
        BufferedInputStream bis = null;
        ByteArrayOutputStream aos = null;
        
        byte[] buffer = new byte[64];
        
        try {
            fis = new FileInputStream(strFile);
            bis = new BufferedInputStream(fis);
            aos = new ByteArrayOutputStream();
            
            while (bis.available() != 0) {
                aos.write(buffer, 0, bis.read(buffer));
            }
        }
        catch (IOException e) {
            System.out.println("File \"" + strFile + "\" could not be read.");
        }
        finally {
            try {
                aos.close();
                bis.close();
                fis.close();
            }
            catch (Exception e) {
                e.printStackTrace();
            }
        }
        
        byte[] data = aos.toByteArray();
        
        if (data.length < 54) {
            System.out.println("File \"" + strFile + "\" is too small to be a valid BMP file.");
        }
        if (data[0] != 'B' || data[1] != 'M')
        {
            System.out.println("File \"" + strFile + "\" has an invalid header for a BMP file.");
        }
        if ((data[29] << 8 | data[28]) != 24)
        {
            System.out.println("File \"" + strFile + "\" must have a color depth of 24bpp.");
        }
        if ((data[33] << 8 | data[32] << 8 | data[31] << 8 | data[30]) != 0)
        {
            System.out.println("File \"" + strFile + "\" must not use compression.");
        }
        
        return data;
    }
    
    private static void writeBMP(String strFile, byte[] header, byte[] data) {
        
        ByteArrayInputStream ais = null;
        BufferedInputStream bis = null;
        FileOutputStream fos = null;
        
        byte[] buffer = new byte[64];
        
        byte[] both = new byte[header.length + data.length];
        System.arraycopy(header, 0, both, 0, header.length);
        System.arraycopy(data, 0, both, header.length, data.length);
        
        try {
            ais = new ByteArrayInputStream(both);
            bis = new BufferedInputStream(ais);
            fos = new FileOutputStream(strFile);
            
            while (bis.available() != 0) {
                fos.write(buffer, 0, bis.read(buffer));
            }
        }
        catch (IOException e) {
            System.out.println("File \"" + strFile + "\" could not be written.");
        }
        finally {
            try {
                fos.close();
                bis.close();
                ais.close();
            }
            catch (Exception e) {
                e.printStackTrace();
            }
        }
    }
    
    private static byte[] encryptBytes(byte[] data) {
        
        byte[] result = null;
        
        try {
            TEKey teKey = new TEKey();
            teKey.attachConnection(conn);
            TECipher teCipher = teKey.exportKey(new byte[0]);
            
            ttag = teCipher.getRawHiddenLink();
            
            result = teCipher.encrypt(data);
            
            teKey.detachConnection();
            
        } catch (TEAgentException e) {
            e.printStackTrace();
        }
        
        return result;
    }
    
    private static byte[] decryptBytes(byte[] data) {
        
        byte[] result = null;
        
        try {
            TEKey teKey = new TEKey();
            teKey.attachConnection(conn);
            TECipher teCipher = teKey.exportKey(ttag);
            
            result = teCipher.decrypt(data);
            
            teKey.detachConnection();
            
        } catch (TEAgentException e) {
            e.printStackTrace();
        }
        
        return result;
    }

    public static void cryptImage(TEAgentConnection conn_, String file_path) {
        
        System.out.println("Attempting to perform image encryption tests on \"" + file_path + "\"...");
        
        conn = conn_;
            
        // typical bitmap file: 54 byte header, 3 bytes per pixel
        
        try {
            
            byte[] header;
            byte[] data;
            byte[] raw;
            
            raw = readBMP(file_path);
            header = Arrays.copyOfRange(raw, 0, 54);
            data = Arrays.copyOfRange(raw, 54, raw.length);
            
            data = encryptBytes(data);
            writeBMP("encrypted.bmp", header, data);
            
            
            raw = readBMP("encrypted.bmp");
            header = Arrays.copyOfRange(raw, 0, 54);
            data = Arrays.copyOfRange(raw, 54, raw.length);
            
            data = decryptBytes(data);
            writeBMP("decrypted.bmp", header, data);

        }
        catch (Exception e) {
            e.printStackTrace();
        }
        
        
    }
}