Process for Embedding Secret Messages in Multiple Cover Images84

Chapter 6 Active and Passive Large-Volume Covert Communication

6.3 Proposed Passive Large-Volume Covert Communication Method for Cover

6.3.2 Process for Embedding Secret Messages in Multiple Cover Images84

We all know that keying in large-volume messages on a cellular phone is not an easy job. With the use of wireless transmission devices of infrared rays or Bluetooth, a user can prepare all messages on a personal computer easily in advance and then use these wireless devices to transmit the messages into a cellular phone.

Cover Images

Figure 6. 6 An illustration of the process for embedding secret messages into multiple

After dividing large-volume secret messages into segments, the proposed system utilizes a 2-LSB data hiding technique to embed each segment in the corresponding cover image. An illustration of the process is shown in Figure 6.6.

6.3.3 Process for Extracting Secret Messages from Multiple Cover Images

An illustration of the process of extracting secret messages from multiple cover images is shown in Figure 6.7.

Large-Volume

Figure 6. 7 An illustration of the process for extracting secret messages from multiple

cover images.

On the receiver site, after collecting all the cover images from the sender site, the proposed system can use an input user key to authenticate each segment of the secret messages and do the combination manipulation.

Large-Volume

Figure 6. 8 A flowchart of the proposed passive large-volume covert communication method for cover images on cellular phones.

A flowchart of the proposed method is shown in Figure 6.8. The sender only needs to input the telephone number of the receiver’s cellular phone and every cover image will be encapsulated as many short message packets and transmitted to the receiver through the wireless transmission of the short messaging system (SMS). At the receiver site, the proposed system can combine each packet to form a complete image and utilizes an input user key to extract and recover the hidden secret messages.

6.4 Experimental Results

In our experiments, two applications, namely, active and passive covert communication, via cover images are elaborated.

(a) (b) Figure 6.9 An experimental result. (a) A browser in the cellular phone. (b) A public

web page. (c) Downloading the JAVA program. (d) An icon of the program. (e) The execution screen of the program. (f) A success extraction with a user key 123. (g) A failed extraction with a user key 12.

(continued)

(e) (f) Figure 6.9 An experimental result. (a) A browser in the cellular phone. (b) A public

(continued)

(g) Figure 6.9 An experimental result. (a) A browser in the cellular phone. (b) A public

(continued)

In the first experiment, while a user utilizes a cellular phone to browse a web page, a website address must be inputted in a browser. Then, a cover image and some descriptions are displayed on the screen. The user can press the button on the cellular phone and download a JAVA program presented in Figure 6.9(c). After the installation is completed, an icon is shown on the main screen. If the user executes the downloaded program, the cover image can be displayed on the screen. While the selection button presented in Figure 6.9(e) is pressed, the user can input a user key to extract secret messages hidden in the cover image. If the provided key is wrong, the extraction process fails, as presented in Figure 6.9(g).

(a) (b)

Taking a picture. (c) A captured image. (d) Keying in secret messages.

(e) The completed embedding process. (f) A cover image in the database. (g) The transmission system on the sender site. (h) The receiving system on the receiver site. (i) Loading of the received cover image. (j) The completed extraction process. (k) A success extraction with a user key 123. (l) A failed extraction with a user key 12.

(continued)

(e) (f)

(g) (h) Figure 6.10 An experimental result. (a) Three icons of the proposed system. (b)

Taking a picture. (c) A captured image. (d) Keying in secret messages.

(continued)

(i) (j)

(k) (l) Figure 6.10 An experimental result. (a) Three icons of the proposed system. (b)

Taking a picture. (c) A captured image. (d) Keying in secret messages.

(continued)

In the second experiment, when a user wants to deliver secret messages to others making use of the proposed system, a picture as a cover image can be taken by the camera built in the cellular phone, as presented in Figure 6.10(b). The user has to key in a user key and the secret messages, and the proposed system can embed them in the cover image. After the embedding process is completed, the user can utilize the wireless network transmission system presented in Figure 6.10(e) to transmit the cover image to others. On the receiver site, a corresponding receiving system should be executed to get the cover image. After the receiving process is completed, the receiver also has to key in an authentic user key to the proposed system to extract the secret messages, as presented in Figure 6.10(i).

6.5 Summary and Discussions

In this chapter, two types of data hiding applications, including active covert communication and passive covert communication, have been proposed and tested. A user can utilize the proposed system and a cellular phone to achieve the purpose of covert communication for data hiding applications.

There are some advantages of using cellular phones as the executing platform against personal computers, as illustrated in the following.

1. The size of a cellular phone is much smaller than a personal computer.

2. The acquisition of a cellular phone is much easier than a personal computer.

3. The ability of wireless connections of a cellular phone is much more convenient than personal computers.

But there are also some benefits of using personal computers as the executing platform against cellular phones illustrated as follows.

1. The computing power of a personal computer is much stronger than that of a

cellular phone.

2. The physical memory of a personal computer is much larger than a cellular phone.

3. The network transmission rate of a personal computer is much faster than a cellular phone.

In fact, the selection of the executing platform depends on applications which we want.

Chapter 7 Image Transmission with

Authentication Capability on Cellular Phones

7.1 Introduction

Since the transmission of cover images on the platform of a cellular phone is exposed on the public wireless network environment, illicit users may intercept these images and edit them for deceiving receivers or misrepresentation. Thus, verifying the validity and the integrity of the transmitted images is necessary.

In Section 7.2, the proposed authentication method for captured images on cellular phones is introduced. This method describes how to generate authentication signals for images and two processes for embedding and extracting of them are also included here. Finally, some experimental results and discussions are given.

7.2 Proposed Authentication Method for Captured Images on Cellular Phones

Because most of modern cellular phones have built-in cameras, they have the

ability of taking pictures. Combined with the wireless network transmission system, cellular phones can help users investigate confidential cases.

Here is an application example. When an employee is investigating classified cases and has to take important pictures for evidences, the employee can utilize a camera built on a cellular phone to accomplish this job. After collecting essential pictures, the employee can transmit them to superiors through the public wireless network environment. After the superiors receive these pictures, they do not know whether the received pictures are genuine or not and can use the proposed system to authenticate them.

In Section 7.2.1, an authentication signal generation method is proposed. After generating authentication signals, two processes for embedding and extracting them are needed, and they are described in Sections 7.2.2 and 7.2.3, respectively.

7.2.1 Method for Generating Authentication Signals

In order to verify the fidelity of captured images, a 4×4 block in an image is taken as an authentication unit. While a suspicious image is being authenticated, the proposed system can check an authentication signal hidden in each 4×4 block. An illustration of a 4×4 block is shown in Figure 7.1 and the corresponding detailed algorithm is described in the following.

Algorithm 1: Generate an authentication signal for a 4×4 block.

Input: a 4×4 block B, a user key K, and each pixel value of a 4×4 block Pi, i = 1, 2, …, 16.

Output: an authentication signal S.

Steps:

2. Calculate the average pixel value of P_i’ and denote it by M.

3. Utilize K and M to generate a random integer R with the length of 32 bits as an authentication signal S.

… … … …

… … …

Captured image Let a 4x4 block be an authentication unit

Figure 7. 1 An illustration of a 4×4 block on a captured image.

7.2.2 Process for Embedding Authentication Signals

After capturing images using a camera built on a cellular phone, a user should take these images and a user key as input to the proposed system. The system uses the method for generating authentication signals mentioned in Section 7.2.1 and a 2-LSB data hiding technique to hide an authentication signal into a 4×4 block. For each block, it has 16 pixels and the system can employ the two least significant bits of each pixel to embed a random integer with the length of 32 bits in the red, green, and blue channels, respectively. A flowchart of the process is shown in Figure 7.2.

… … … …

… … …

Captured Images

Key

Captured Images with Authentication Signals Generate

Authentication Signal

Take Pictures

Embed Authentication Signal

… … …

Captured image Let a 4x4 block be an

authentication unit

Figure 7. 2 An illustration of the process for embedding authentication signals in a captured image.

7.2.3 Process for Extracting Authentication Signals

While the receiver gets a suspicious image, the system can utilize an input user key and the corresponding mean value of each block to regenerate an authentication

signal. If an extracted authentication signal and a regenerated one is the same, the current block can be considered as authentic, otherwise, it is thought unauthentic. The extraction process is an inverse of the embedding one and both of them utilize the 2-LSB data hiding technique. A flowchart of the process is shown in Figure 7.3

… … … … Let a 4x4 block be an authentication unit

Figure 7. 3 An illustration of the process for extracting authentication signals from a

captured image.

An illustration of the proposed method is shown in Figure 7.4. Both the sender and the receiver should take the same user key as input for correct verification of suspicious captured images. At the sender site, the receiver’s cellular phone number should be input to the proposed system and all data are transmitted to the receiver site through the public wireless network.

Captured

Figure 7. 4 An illustration of the proposed authentication method for captured images

on cellular phones.

7.3 Experimental Results

An example of our experiments is illustrated here, as shown in Figure 7.5. In our experiments, a protected captured image was transmitted on the platform of a cellular phone. While a user wants to take a picture, with the use of the proposed system, a captured image can be taken, as illustrated in Figure 7.5(b). After the process of embedding authentication signals in the captured image is completed, the user can transmit the image to others. On the receiver site, the receiver also has to key in a user key into the proposed system to verify the validity of the received image, as illustrated in Figure 7.5(i).

(a) (b) Figure 7.5 An experimental result. (a) Three icons of the proposed system. (b)

Taking a picture. (c) A captured image. (d) Embedding authentication signals. (e) A captured image in the database. (f) The transmission system on the sender site. (g) The receiving system on the receiver site.

(h) Loading of the received captured image. (i) A success authentication with a user key 123. (j) A failed authentication with a user key 12.

(continued)

(e) (f) Figure 7.5 An experimental result. (a) Three icons of the proposed system. (b)

with a user key 123. (j) A failed authentication with a user key 12.

(continued)

(g) (h)

(i) (j) Figure 7.5 An experimental result. (a) Three icons of the proposed system. (b)

(h) Loading of the received captured image. (i) A success authentication with a user key 123. (j) A failed authentication with a user key 12.

(continued)

7.4 Summary and Discussions

In this chapter, an authentication method for captured images on the platform of a cellular phone is proposed and experimented. If the authentication method only adopted a user key to generate random integers, illicit users could intercept transmitted images and modify them by copying the two least significant bits of each pixel of intercepted images to produce fake images for misrepresentation. The receiver cannot find out any difference between them.

With the use of a corresponding mean value of a 4×4 block and a user key, the security of the proposed method is improved and users can verify the fidelity of suspicious captured images without using authentication signatures.

Chapter 8 Conclusions and Suggestions for Future Works

8.1 Conclusions

In this study, we have proposed several data hiding methods for various application purposes, such as covert communication, authentication, and copyright protection. And some of them are implemented on the platform of a cellular phone in addition to on personal computers.

For covert communication, three methods for two different application platforms have been proposed. First, an active covert communication method implemented on a web page has designed to transmit large-volume secret messages using MPEG videos as cover media on the platform of a personal computer. Users can get secret messages from the public Internet more securely and more easily. Second, an active covert communication method which is also implemented on a web page has proposed to transmit secret messages using images as cover media on the platform of a cellular phone. Users can get secret messages from the public wireless network securely and easily. Finally, a method implemented on the platform of a cellular phone has been designed to transmit large-volume secret messages using multiple images as cover media. Users can get and transmit secret messages to each other via the proposed system. These three methods are also capable of verifying the fidelity of hidden secret messages.

For copyright protection, two active copyright protection methods using digital

watermarking techniques have been proposed. Both of these two methods can be used to protect MPEG videos on a web page. One method transforms removable visible watermarks into invisible ones on the MPEG videos. Multimedia providers can use this method to check if a user, who wants to see videos, has an authentic key. Another method transforms invisible watermarks to visible ones on the MPEG videos.

Multimedia providers can use this method to prevent illicit users from downloading and editing the videos for misrepresentation.

For authentication, two methods for two different application platforms have been proposed. First, an active authentication method implemented on a web page has been proposed to verify the integrity and the fidelity of MPEG videos on a web page.

Users can obtain and authenticate the MPEG videos with work assignments pasted on a public web page without the need of installing authentication programs. Second, a method implemented on the platform of a cellular phone was proposed to authenticate images which are captured by a camera built in a cellular phone. Users can transmit captured images and utilize the proposed system to verify the fidelity of them.

8.2 Suggestions for Future Works

Several suggestions for future researches are enumerated as follows.

1. Active information hiding techniques, such as covert communication, copyright protection and authentication of MPEG videos, may be integrated in a new method.

2. Active information hiding applications may be developed on different media, such as text, audio, image, and video.

3. Active information hiding applications may be developed on more

4. Passive information hiding techniques on the platform of a cellular phone may be extended to deal with more types of multimedia and the latest technology can be utilized to transmit data in a faster way.

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