State Of The Art In Digital Steganography Focusing ASCII Text Documents

Abstract— Digitization of analogue signals has opened up new avenues for information hiding and the recent advancements in the telecommunication field has taken up this desire even further. From copper wire to fiber optics, technology has evolved and so are ways of covert channel communication. By “Covert” we mean “anything not meant for the purpose for which it is being used”. Investigation and detection of existence of such cover channel communication has always remained a serious concern of information security professionals which has now been evolved into a motivating source of an adversary to communicate secretly in “open” without being allegedly caught or noticed. This paper presents a survey report on steganographic techniques which have been evolved over the years to hide the existence of secret information inside some cover (Text) object. The introduction of the subject is followed by the discussion which is narrowed down to the area where digital ASCII Text documents are being used as cover. Finally, the conclusion sums up the proceedings. Keywords- Steganography, Cryptography, Conceal, Steganology, Covert Channel I. INTRODUCTION Cryptography derived from Greek, (where historian Plutarch elaborated on the use of scytale – an encryption technique via transposition, a thin wooden cylinder, by a general for writing message after wrapping it with paper, to decrypt the message, one needs to wrap that piece of paper again on the scytale to decrypt the message [41].), focuses on making the secret information unintelligible.

   Information Hiding Men’s quest to hide information is 

best put in words [2] as “we can scarcely imagine a time when there did not exist a necessity, or at least a desire, of transmitting information from one individual to another in such a manner as to elude general comprehension”.

While discussing information hiding, we mainly come across people from two schools of thought. One votes for making the secret information unintelligible (encryption) [5] whereas the other like Eneas the Tactician, and John Wilkins [4][5] are in favor of hiding the existence of the information being exchanged (steganography) because of the fact that the exchange of encrypted data between Government agencies, parties etc. has its obvious security implications.

• Covert/Subliminal Channel A communication channel which is not explicitly designed for the purpose for which it is being used [6][7] e.g. using TCP & IP header for hiding and sending secret bits etc. • Steganography is derived from the Greek words
, ‘steganos’ and ‘graphie’, [8] which means Covered Writing/Drawing.

The classic model for invisible communication was first proposed by Simmons [3][4] as the prisoners’ problem who argued by assuming, for better understanding, that Alice and Bob, who have committed a crime, are kept in separate

Figure 1 – Scytale [44]

Figure 2 – Classification of Information Hiding based on [1]

Figure 3 – Prisoner’s Problem 63 http://sites.google.com/site/ijcsis/ ISSN 1947-5500 (IJCSIS) International Journal of Computer Science and Information Security,
Vol. 7, No. 2, 2010 cells of a prison but are allowed to communicate with each other via a warden named Wendy with the restriction that they will not encrypt their messages and that the warden can put them in isolated confinement on account of any suspicious act while in communication. In order to plan an escape, they now need a subliminal channel so as to avoid Wendy’s intervention.

Following is an example from [34] where in World War I, German Embassy in Washington (DC) sent the following telegram messages to its Berlin headquarters (David Kahn 1996):

“PRESIDENT’S EMBARGO RULING SHOULD HAVE IMMEDIATE NOTICE. GRAVE SITUATION AFFECTING INTERNATIONAL LAW. STATEMENT FORESHADOWS RUIN OF MANY NEUTRALS. YELLOW JOURNALS UNIFYING NATIONAL EXCITEMENT IMMENSELY.

APPARENTLY NEUTRAL’S PROTEST IS THOROUGHLY DISCOUNTED AND IGNORED. ISMAN HARD HIT. BLOCKADE ISSUE AFFECTS PRETEXT FOR EMBARGO ON BYPRODUCTS, EJECTING SUETS AND VEGETABLE OILS.” [34]

By concatenating the first character of every word in the first message and the second character of every word in the second message the following concealed message is retrieved:

“PERSHING SAILS FROM NY JUNE I” [34]

At present Int

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