Steganography is the process of hiding a secret message within a larger one in such a way that someone cannot know the presence or contents of the hidden message. Although related, Steganography is not to be confused with Encryption, which is the process of making a message unintelligible—Steganography attempts to hide the existence of communication.

The main advantage of steganography algorithm is because of its simple security mechanism. Because the steganographic message is integrated invisibly and covered inside other harmless sources, it is very difficult to detect the message without knowing the existence and the appropriate encoding scheme .

Proposed Algorithm

The algorithm is more dedicated towards the algorithm proposed by Rosziati Ibrahim and Teoh Suk Kuan in their Research Paper published on February 25, 2011.

Encoding Algorithm

Firstly, the secret message that is extracted is compressed as the contents in the compressed string will significantly hard to detect and read, furthermore it reduces the size of string.
Secondly, the compressed string is encrypted with the secret key.
Finally, encoding the encrypted message in the image. It uses LSB steganographic embedding to encode data into an image. Once the message is encoded the process stops.

LSB(Least Significant Bit) Embedding

The LSB is the lowest significant bit in the byte value of the image pixel.

The LSB based image steganography embeds the secret in the least significant bits of pixel values of the cover image (CVR).

The concept of LSB Embedding is simple. It exploits the fact that the level of precision in many image formats is far greater than that perceivable by average human vision. Therefore, an altered image with slight variations in its colors will be indistinguishable from the original by a human being, just by looking at it. In conventional LSB technique, which requires eight bytes of pixels to store 1byte of secret data but in proposed LSB technique, just four bytes of pixels are sufficient to hold one message byte. Rest of the bits in the pixels remains the same. Following shows the bit level interpretation of the algorithm :

Decoding Algorithm

Firstly, decode the message from the encrypted image using LSB decoding.
Secondly, decrypt the compressed message from the decoded message using the secret key.
Finally, decompress the message to get the original compressed message.

Consider the following encoding, it is totally undetectable by human eyes.

Usage

Just add the following dependency in your app’s build.gradle

dependencies {
      implementation 'com.github.aagarwal1012:Image-Steganography-Library-Android:v1.0beta'
}

How to encode message into an image ?

Note : Your Activity class should implements TextEncodingCallback interface and also contains its override methods.

public class MainActivity extends AppCompatActivity implements TextEncodingCallback 

Firstly, instantiate the ImageSteganography object and pass the values Message , Secret Key and Image Bitmap to the constructor.

ImageSteganography imageSteganography = new ImageSteganography(message, 
                                        secret_key, 
                                        original_image);

Secondly, instantiate the TextEncoding object and pass the values Activity and TextEncodingCallback object to the constructor.

TextEncoding textEncoding = new TextEncoding(MainActivity.this,
                            MainActivity.this);

Finally, execute our encoding task.
```
textEncoding.execute(imageSteganography);
```
Note : By default a ProgressDialog will appear in the process of text encoding.

Override Methods

OnStartTextEncoding() : In this method you can whatever by the start of text encoding process.

@Override
    public void onStartTextEncoding() {
        //Whatever you want to do at the start of text encoding
    }

onCompleteTextEncoding() : After the completion of text encoding, this method is called and gives result.

@Override
    public void onCompleteTextEncoding(ImageSteganography result) {
  
        //After the completion of text encoding.
          
        //result object is instantiated 
        this.result = result;
  
        if (result != null && result.isEncoded()){
              
            //encrypted image bitmap is extracted from result object
            encoded_image = result.getEncrypted_image();
              
            //set text and image to the UI component.
            textView.setText("Encoded");
            imageView.setImageBitmap(encoded_image);
    }

How to decode message from an image ?

Note : Your Activity class should implements TextDecodingCallback interface and also contains its override methods.

public class MainActivity extends AppCompatActivity implements TextDecodingCallback 

Firstly, instantiate the ImageSteganography object and pass the values Secret Key and Image Bitmap to the constructor.

ImageSteganography imageSteganography = new ImageSteganography(secret_key,
                                        original_image);

Secondly, instantiate the TextDecoding object and pass the values Activity and TextDecodingCallback object to the constructor.

TextDecoding textDecoding = new TextDecoding(MainActivity.this, 
                            MainActivity.this);

Finally, execute our decoding task.
```
textDecoding.execute(imageSteganography);
```
Note : By default a ProgressDialog will appear in the process of text decoding.

Override Methods

OnStartTextDecoding() : In this method you can whatever by the start of text decoding process.

@Override
    public void onStartTextDecoding() {
        //Whatever you want to do at the start of text encoding
    }

onCompleteTextDecoding() : After the completion of text decoding, this method is called and gives result.

@Override
    public void onCompleteTextEncoding(ImageSteganography result) {
  
        //After the completion of text encoding.
          
        //result object is instantiated 
        this.result = result;
  
        if (result != null){
              
            /* If result.isDecoded() is false, it means no Message was found in           the image. */
            if (!result.isDecoded())
                textView.setText("No message found");
              
            else{
                /* If result.isSecretKeyWrong() is true, it means that secret key provided        is wrong. */ 
                if (!result.isSecretKeyWrong()){
                    //set the message to the UI component.
                    textView.setText("Decoded");
                    message.setText("" + result.getMessage());
                }
                else {
                    textView.setText("Wrong secret key");
                }
            }
        }
        else {
            //If result is null it means that bitmap is null
            textView.setText("Select Image First");
        }
    }

Documentation

ImageSteganography Class

Java attribute	Java set methods	Description	Default Value
Message	setMessage(…) , getMessage()	Set the value of message, Get the value of message.	Null
Secret_Key	setSecret_key(…)	Set the value of secret key.	Null
Image	setImage(…)	Set the value of image.	Null
Encoded_Image	getEncoded_image()	Get the value of encoded image after text encoding.	Null
Encoded	isEncoded()	Check that the encoding is over or not	false
Decoded	isDecoded()	Check that the decoding is over or not.	false
SecretKeyWrong	isSecretKeyWrong()	Check that the secret key provided was right or wrong but after decoding was done.	true

Want to contribute !

This is the well documented library. I have documented each and every method that I have used, so go to the GitHub and have a good read to the code and suggest some changes and new feature to be added in the library.
Feel free to open an issue.

If you find any problem leave a comment below.

Ayush Agarwal

Image Steganography Library for Android

Proposed Algorithm

Encoding Algorithm

LSB(Least Significant Bit) Embedding

Decoding Algorithm

Usage

How to encode message into an image ?

Override Methods

How to decode message from an image ?

Override Methods

Documentation

ImageSteganography Class

Want to contribute !