Şeref
SAĞIROĞLU / Erciyes University, Faculty of Engineering, Department of Computer
Engineering, ss@erciyes.edu.tr
Mehmet
TUNÇKANAT / İvme Mühendislik, tunckanat@ivmemuhendislik.com
Mehmet ALTUNER / Telecommunication Authority, maltuner@tk.gov.tr
A
New Approach in Criptology: Picture Message
COMPREHENSIVE
SUMMARY
1.
Introduction
Societies, which
give value to information, are spending great efforts for using and developing
information in all spheres and the requisite of being an information society
is fulfilled. Human beings, while increasing and developing the existing accumulation
of information, are spending great amount of money and labor in order to keep
this information in a safe 
environment.
When the fact that existing information increases twofold annually is taken
into consideration, it is apparent that it will be more important in the future.
In a period when digital world is ever more permeating our lives day by day,
our personal rights and liberties and private lives will be affected from this
to a great extent. The digitalisation of the functions in our daily lives is
a signifier of this development. While this ratio is at the level 60 % in the
United States, it is below 10 % in our country, its majority being consisted
of banking transactions.
Today, the safety of information is important from a personal aspect. However,
it displays much more significance for those units/institutions, which work
and function for the guarantee of the future of some societies. Military practices
are one of the outstanding examples for them. According to a report made public
35 years after the Second World War, the development of the war between United
Kingdom and Germany was changed by the decoding of the messages that contained
war tactics and this played a great a role in the victory of Allied countries.
Boston Globe, in one of its news has emphasised that this event is so important
that it would require changes in history books on Second World War, which had
previously been written. The event of decoding, which is so important as to
mold history is one of most illustrative examples that can be given to emphasised
the importance of this topic. Today, it is possible to find millions of really
astonishing examples. The rapid expansion of digitalisation in the word of information
has made the usage of coding methods and encrypting systems for both personal
and institutional data safety [1].
Cryptology, is the branch
of mathematics, which contains both the science of coding (cryptography) and
cipher analysis (crypto-analysis). The term terminologically descends from the
Greek Kryptos Logos, which means secret. The aim of the science of coding is
to maintain the safety of the sent and received data. The aim of cipher analysis
is decoding the existing ciphers.
Coding is the process through which the content of a message (plain text) is
made unreadable without appropriate information (key information). The aim of
coding is to prevent the reading of the message by those unwanted persons. Decoding,
on the other hand, is just the opposite of coding, which is the process through
which the coded text is transformed into plain text.
2.
New approach method
In recent years we come across Steganography as a new approach method [1-4].
This approach might briefly be described as the hiding of a datum into an object.
Datum can be hidden on voice, picture, video images. While these data can be
a text file, it is also possible to hide into an image another image.
The approach in this study is about how a datum can be hidden into digital pictures.
In order to explain this a typical digital picture is provided in Figure 1.
A line of N rows and M columns (Figure 1) represents this picture. Row and columns
indexes might generally be displayed as y and x or r and c. Picture line is
mostly (not all) is square-shaped. Thus, it might be that 
N
= M and typical N and M values are such as 128, 256, 512 or 1024.
The elements of such a
picture line are called pixel and in the simplest condition pixels take the
value of 0 or 1. The pictures that are composed of these pixels are called binary
pictures and 1 and 0 values generally represent subsequently the bright and
dark areas or the object and ground (surrounding ground in front of or on which
the object is situated). For better grading the intensity of light of video
pictures 1 byte is used per pixel. In this way, it is possible to get perfect
numbers between 0 (black) and 255 (white). The values between these numbers
are gray and for this reason the perfect number that belongs to a picture is
named as the gray level. In coloured pictures, on the other hand, a picture
requires a NxM line for each and every one of basic colours such as red, green
and blue. Thus, the "gray level"s of every line determines the intensity
of the components of red, green and blue pictures of a pixel in a certain position.
In order to understand the process that is conducted here, it is required that
the concept of least significant byte (LSB: Least Significant Byte), shall be
understood. Let us consider number 10110111 according to the binary numerical
system. When we transform this base two number into decimal we get number 183.
Whether the last (LSB) byte is 1 or 0 will not cause a major change in this
number. If the value of the last byte was 0 its decimal equivalent would be
182 and this will not cause a significant change in colour. Hence, datum that
is considered to be hidden can be located in the place of LSBs.
3. Application
Let us discuss the consequences of the approach that is explained above by illustrating
an example of the application of this approach: With this aim in mind, studies
have been conducted on BMP format, which is included among the existing picture
formats and BMP formatted picture of Great Leader Atatürk was selected as an
example (Figure 2). The Address of Atatürk to the Youth was selected as the
document that will be hidden into the picture. In order to display the approach
that is provided here, a software that conducts the above explained processes
was automatically developed in Delphi environment. The document that will be
automatically hidden by this software was hidden into the picture that is provided
in Figure 3. When the pictures are compared it is clear that the difference
between them cannot be observed visually.
When the picture
in which datum is hidden is sent with an ordinary message by e-mail or another
electronic communication means, a person who regulates internet traffic or receives
the message will only be able to read the message and see the picture attached
to the message.
A document, which is hidden in any picture does not change the size of the picture.
This is an expected result. The fact that there is no change in size, is another
sign of the success of coding. In order to retrieve the datum that is hidden
it is possible to realise the process in the opposite direction by the software
that we developed and to retrieve the document by reading the LSB bytes. Examplary
window printouts related to Coding and Decoding processes realised by the software
developed are provided in Figure 4
In present times when information is rapidly increasing and safety is gaining
ever more importance the new approach, which was prepared for sending documents
under safe conditions was ended with success. Since this approach is turned
into a ready program it can easily and safely be used by the users. The only
disadvantage of this approach is that the length of the message that will be
sent depends on the size of picture. It is required that pictures with high
resolution and size be used for long messages.
5. References
[1]. Information Hiding Techniques for Steganography and Digital
Watermarking, Katzenbeisser and Petitcolas (Editors), Artech House, Computer
Security Series, Jan. 2000.
[2]. http://www.teknohaber.net/makale.php?id=20104
[3]. http://www.jjtc.com/Steganography
[4]. http://www.all-nettools.com/privacy/stegano.htm