This paper introduces steganography, the art and science of hidden writing. The purpose of steganography is to hide the existence of a secret message from a third party. The most popular modern application of steganography involves concealing messages within least significant bits of image or sound files. Another application of modern steganography is a steganographic file system. Steganography is also used by some modern printers, where tiny yellow dots that contain encoded printer serial numbers, as well as other information, are added to each printed page. I chose modern steganography as a topic for my course paper primarily because I have had an interest in the topic before, and would like to use this paper as an opportunity to expand my knowledge of steganographic techniques, especially in their modern applications.
In this paper, we will introduce what steganography is and what kind of applications can be expected. Steganography is an art and science of hidding information within other information. The word itself comes from Greek and means ”hidden writting”. First complex book cover- ing steganography was written by Johannes Trithemius in 1499. The book Steganographia itself was published later in 1606 and immediately placed on the Index Librorum Prohibitorum. In recent years cryptography become very popular science. As stega- nography has very close to cryptography and its applications, we can with advantage highlight the main differences. Cryptography is about conceal- ing the content of the message. At the same time encrypted data package is itself evidence of the existence of valuable information. Steganogra- phy goes a step further and makes the ciphertext invisible to unautho- rized users. Hereby we can de ne steganography as cryptography with the additional property that its output looks unobtrusively. Secret data
| Unobtrusive media
c=c>y)c+=y=i^i/8^i>>4^i>>12,i=i>>8^y<<17 Encrypted data
0101 1001 10 1 01 1 01 01 1 01 01 10
01 1 1 01 0 1 1 10 0 0 1 1 0 01 1 10 10
01 1 0 1 01 01 10 10 0 1 0011 1 1 11
01 1 1 01 11 1 001 11 001 1 0 1 1 1 01
One can ask what is it good for. Well, image the common situation when you encrypt your important business data. Suddenly robbers cap- ture and torture you into revealing cryptographics keys. As well police power may be abused. They ask you to give them the private keys or you are highly suspicious of committing crime. Next, what if the police is bribed. Would not it be better, if you can plausibly deny the existence of important data? A famous example of steganography is Simmons' ”Prisoners' prob- lem”, see . Bob and Alice are in a jail and wish to escape. Their cells are far apart from each other and the only allowed communication is sending messages via prison of cer. If warden detects any sign of con- spiracy, he will secure their cells even more. Bob and Alice are well aware of these facts. Happily, before they got arrested, they have agreed a stegosystem. Stegosystem describes the way the secret message is embedded into a co- vertext (seemingly innocent message). According to the standard termi- nology of information hidding a covertext with hidden information is called stegotext. Examples of historical stegosystems can be secret inks, wax tablets or microdots used during WWII. In modern era these methods can invoke smile on face, but image their power, when they were not widely known. Nowadays methods still hold the same simplicity, just exploit advantages of digital media and communications. We can distinguish between stegosystems with passive warder and active warder. Passive warder just monitors the communication channel. He can pass the covertexts throught several statistical tests, but do not modify them. It is the same situation as when the network packets go...
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