Applications of Steganography
Steganography is applicable to, but not limited to, the following areas.
1) Confidential communication and secret data storing
2) Protection of data alteration
3) Access control system for digital content distribution
4) Media Database systems
The area differs in what feature of the steganography is utilized in each system.
1. Confidential communication and secret data storing
The "secrecy" of the embedded data is essential in this area.
Historically, steganography have been approached in this area. Steganography provides us with:
(A) Potential capability to hide the existence of confidential data
(B) Hardness of detecting the hidden (i.e., embedded) data
(C) Strengthening of the secrecy of the encrypted data
In practice, when you use some steganography, you must first select a vessel data according to the size of the embedding data. The vessel should be innocuous. Then, you embed the confidential data by using an embedding program (which is one component of the steganography software) together with some key. When extracting, you (or your party) use an extracting program (another component) to recover the embedded data by the same key ( "common key" in terms of cryptography). In this case you need a "key negotiation" before you start communication.
Attaching a stego file to an e-mail message is the simplest example in this application area. But you and your party must do a "sending-and-receiving" action that could be noticed by a third party. So, e-mailing is not a completely secret communication method.
There is an easy method that has no key-negotiation. We have a model of "Anonymous Covert Mailing System." See the reference .
There is some other communication method that uses the Internet Webpage. In this method you don't need to send anything to your party, and no one can detect your communication. This method is shown in the other page.
Each secrecy based application needs an embedding process which leaves the smallest embedding evidence. You may follow the following.
(A) Choose a large vessel, larger the better, compared with the embedding data.
(B) Discard the original vessel after embedding.
For example, in the case of Qtech Hide & View, it leaves some latent embedding evidence even if the vessel has a very large embedding capacity. You are recommended to embed only 25% or less (for PNG / BMP output) of the maximum capacity, or only 3% of the vessel size (for JPEG output)..
2. Protection of data alteration
We take advantage of the fragility of the embedded data in this application area.
We asserted in the Home Page that "the embedded data can rather be fragile than be very robust." Actually, embedded data are fragile in most steganography programs. Especially, Qtech Hide & View program embeds data in an extremely fragile manner. We demonstrate this in the other page.
However, this fragility opens a new direction toward an information-alteration protective system such as a "Digital Certificate Document System." The most novel point among others is that "no authentication bureau is needed." If it is implemented, people can send their "digital certificate data" to any place in the world through Internet. No one can forge, alter, nor tamper such certificate data. If forged, altered, or tampered, it is easily detected by the extraction program. Just visit this page and see the reference .
3. Access control system for digital content distribution
In this area embedded data is "hidden", but is "explained" to publicize the content.
Today, digital contents are getting more and more commonly distributed by Internet than ever before. For example, music companies release new albums on their Webpage in a free or charged manner. However, in this case, all the contents are equally distributed to the people who accessed the page. So, an ordinary Web distribution scheme is not suited for a "case-by-case" and "selective" distribution. Of course it is always possible to attach digital content to e-mail messages and send to the customers. But it will takes a lot of cost in time and labor.
If you have some valuable content, which you think it is okay to provide others if they really need it, and if it is possible to upload such content on the Web in some covert manner. And if you can issue a special "access key" to extract the content selectively, you will be very happy about it. A steganographic scheme can help realize a this type of system.
We have developed a prototype of an "Access Control System" for digital content distribution through Internet. The following steps explain the scheme.
(1) A content owner classify his/her digital contents in a folder-by-folder manner, and embed the whole folders in some large vessel according to a steganographic method using folder access keys, and upload the embedded vessel (stego data) on his/her own Webpage.
(2) On that Webpage the owner explains the contents in depth and publicize worldwide. The contact information to the owner (post mail address, e-mail address, phone number, etc.) will be posted there.
(3) The owner may receive an access-request from a customer who watched that Webpage. In that case, the owner may (or may not) creates an access key and provide it to the customer (free or charged)..
In this mechanism the most important point is, a "selective extraction" is possible or not.
We have already developed such a selective extraction program to implement the system. We have a downloadable demo program on the other page.
4. Media Database systems
In this application area of steganography secrecy is not important, but unifying two types of data into one is the most important.
Media data (photo picture, movie, music, etc.) have some association with other information. A photo picture, for instance, may have the following.
(1) The title of the picture and some physical object information
(2) The date and the time when the picture was taken
(3) The camera and the photographer's information
Formerly, these are annotated beside the each picture in the album.
Recently, almost all cameras are digitalized. They are cheap in price, easy to use, quick to shoot. They eventually made people feel reluctant to work on annotating each picture. Now, most home PC's are stuck with the huge amount of photo files. In this situation it is very hard to find a specific shot in the piles of pictures. A "photo album software" may help a little. You can sort the pictures and put a couple of annotation words to each photo. When you want to find a specific picture, you can make a search by keywords for the target picture. However, the annotation data in such software are not unified with the target pictures. Each annotation only has a link to the picture. Therefore, when you transfer the pictures to a different album software, all the annotation data are lost.
This problem is technically referred to as "Metadata (e.g., annotation data) in a media database system (a photo album software) are separated from the media data (photo data) in the database managing system (DBMS)." This is a big problem.
Steganography can solve this problem because a steganography program unifies two types of data into one by way of embedding operation. So, metadata can easily be transferred from one system to another without hitch. Specifically, you can embed all your good/bad memory (of your sight-seeing trip) in each snap shot of the digital photo. You can either send the embedded picture to your friend to extract your memory on his/her PC, or you may keep it silent in your own PC to enjoy extracting the memory ten years after. Qtech Hide & View v02 may be a good program for such purposes.
If a "motion picture steganography system" has been developed in the near future, a keyword based movie-scene retrieving system will be implemented. It will be a step to a "semantic movie retrieval system."
The following Website will introduce you to an interesting application of steganography (especially, BPCS) in embedding XML data in archival document image data .
5. To wrap up this page
We have exemplified four steganography-applicable areas, and provided some technical information.
 Eiji Kawaguchi, et al: A Model of Anonymous Covert Mailing System Using Steganographic Scheme, in INFORMATION MODELLING AND KNOWLEDGE BASES XIV, H. Yaakkola et al (Eds), IOS Press, pp.81-85, 2003. (Download: 182KB)
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(Updated: Aug. 21, 2009 by Eiji Kawaguchi)