Steganography. John Von Dollen. Ron Lepper. Coen 150: Information Security Systems

Transcription

1 Steganography John Von Dollen Ron Lepper Coen 150: Information Security Systems May 17, 2004

2 Abstract: While technology increases, the amount of privacy provided by simply encrypting a message decreases. So, the need for a more secure and private form of communication arises. One method that comes forth to provide a solution to this problem is steganography. This paper will introduce basic concepts of steganography, while discussing its positive and negative attributes. I. Introduction to Steganography Steganography, in short, is hiding information in another medium so that the information is both undetectable as well as unrecognizable. In this way, it may be right in front of a person and they would never guess its presence. Steganography has become more common with the advancements of technology and has taken on many forms, increasing its effectiveness. This effectiveness, combined with modern encryption algorithms makes a perfectly undetectable, undecipherable means of communication. Steganography, literally meaning covered writing, comes from the Greek words steganos, meaning covered, and graphia, meaning to write. The Ancient Greeks employed the first recorded use of steganography in history. They were known to use two different methods to hide messages. One method that has been discovered was to shave the head of the messenger and tattoo the message on his scalp, hiding it when his

3 hair grew back in, only to be shaved again when the message was delivered. Another method was to carve the message on a wood backing of a wax tablet and cover the tablet with a fresh layer of wax, so that the tablet was seemingly blank. Another method of steganography that has been used in the past was invisible ink. Messages could be written with inks made from onion juice or ammonia salts which could not be seen under a normal light but would glow when held over a flame. Message hiding always seems important in times of war, and was so in WWII, as the Germans used microdots, taking pictures of a message and shrinking them to the size of a period. German spies also hid messages by encoding messages within messages. One message that was actually sent was: Apparently neutral s protest is thoroughly discounted and ignored. Isman hard hit. Blockade issue affects pretext for embargo on by-products, ejecting suets and vegetables oils. Taking the second letter of each word in the message reveals the hidden message: Pershing sails from NY June 1. Now, with the rise in technology, computers are able to conceal messages. Now, people are able to use computers to hide messages in anything from picture to music to video files. In today s methods, the information is hidden in the least significant bits of the files to contain some message. By changing these bits, the actual file does not appear as if it changed at all, but now there is extra information that can be extracted if its presence is known. Such a change would be difficult to detect with the naked eye, so it

4 can be seen as a blessing to those who value privacy and a problem to those whose job it is to find secrets for the protection of others. II. A Discussion on Steganography Steganography is a very powerful means of message hiding, which, given the worlds current demand for information while requiring the maximum privacy to any and all people, means that it is the most secure method for communications. The boom of the internet has created a new demand for steganography. With new technological means of communications, most importantly the internet and s, the public demand for both security and privacy has lead to increased efforts in finding a more secure method for communicating. This demand has lead to increased research into the development of better steganographic methods for these communication mediums. The internet provides an entry point to a global network of information and communication from nearly anywhere in the world. In this way, it is the cheapest, easiest, most desirable means of both long distance and local communication available. Someone on the other side of the world can send you a message that you will receive nearly instantaneously for a reasonable price, creating a highly popular and demanded communications system. As with all means of communications, the parties doing the communicating wish for total security and privacy of their transactions. With digital communications, it is nearly impossible to tell if your communications have been intercepted by another party. Therefore, more and more and communications companies are turning to higher levels of encryption for their customers in the hope that

5 if the communications are intercepted, the intercepting party will not be able to read the contents of the message. Cryptography itself has come a long ways recently, jumping from encryption algorithms that would take months to break to algorithms that would take millions of years to break. However, some government security organizations, such as the NSA, want companies to create backdoors into their encryption algorithms so that they would be able to read any message they thought was a possible threat to national security. These security measures will never be implemented since this violates the privacy of all online communications, and if companies decided to follow through with these backdoors, they would undoubtedly lose their customers. Because of this, cryptography has been able to grow in strength and efficiency to such an extent that no one has a chance at cracking them without the use of a supercomputer which could still take years to crack the code. However, encryption still leaves some information to help crackers in their job: the encrypted file. It is only logical that if a person is intent on cracking an encrypted file they have in their possession, then time is their only opposition. With technology continually advancing, the processing speed of computers keeps getting faster, thus decreasing the time needed to crack the file. However, if the person does not have the encrypted file and instead must find it first, then this adds another layer of security, for if the person does not have the file, then they have to spend more time looking for it. Because steganography is the act of hiding information so that no one will find it, the attacker does not even know where to begin looking; the message could be hidden anywhere: in

6 another text document, in a picture, or even in a movie. This idea combined with the changing technology opens the doors for all sorts of hiding places for information. As previously stated, early forms of steganography were in physical form, meaning the information was hidden on some sort of tangible object such as a letter or even someone s head. Because of this, places to hide information were limited and, therefore, easy to check for. The digital age has generated a number of new areas in which to hide information, most of which are intangible and undetectable by the human eye, making it extremely hard to detect the presence of a piece of information hidden in digital media. For the people looking for a way to communicate secretly, especially on the internet, this method is perfect: not only can you encrypt your message using the best encryption algorithms available, but you can also hide the message in any number of files and formats. The need of detection of an actual file with extra information in it drastically decreases the probability that someone will be able to decrypt your communications. The advancement of the digital world has led to many new forms of mediums, and each medium requires a different algorithm to hide each file type inside of it. Most of the time, images are the desired files for hiding information. One reason for this is that not many people would expect to find any hidden information inside of a picture. Text is actually very easily hidden in a bitmap file because of the file format of bitmaps. The bitmap files actually contain the color of each pixel of the image in the form of a certain number of bits (depending on the compression and resolution desired of the image). So, if a pixel is white, its 8 byte representation would be FF FF FF FF FF FF 00 00, and black would be In this way, one could easily change the least significant bit of each pixel without changing the color noticeably. By changing each

7 pixel in succession this way to the binary representation of the message, one could successfully record a message in the pixels of the image without appearing to change the image or size of the file. Essentially, all digital files are made up of binary. It is no surprise that you could use an algorithm like the one in the previous example to hide a message in other digital mediums like videos or audio files. However, in order for the files to open and display properly in such a way that the file has not been altered, the algorithm needs to be changed. Altering the video file requires one to not noticeably change neither the audio nor the video quality. The most important part is to alter the file so that any normal human would not be able to notice the changes. This means that when hiding something in a video file, you must be certain that the changes do not affect the video quality enough to become noticeable to the human eye. In audio files, adding a message to the file sometimes creates a glitch in the sound. This is not a problem as long as the glitch is so minute that a human ear cannot detect the difference. These alterations are mostly performed in a method that will create the least amount of detection to increase their effectiveness. As soon as a newer, harder to detect algorithm is created, people try to figure out faster, cleverer ways of detecting these hidden files and messages, thus creating a continual demand for yet newer algorithms and methods of steganography. This demand, along with the demand for public privacy as we increase access to security products, has created many open source programs free to the public. As long as there is a demand for personal privacy, there will always be someone willing to create ways of obtaining it. Therefore, sites with steganographic knowledge and freeware will always be available to anyone with access to the internet.

8 While steganographic and cryptographic tools are available freely throughout the internet to the general public, it is also available to those with ill intentions. This creates a very dangerous threat since the communications method is nearly invisible as well as uncrackable given today s encryption and decryption methods. Not only can normal, upstanding citizens communicate privately without anyone knowing it, but so can criminals. The internet has created an endless galaxy of information and knowledge. Likewise, it has created an infinite amount of places to hide information, making it especially hard to trace any illegal communication. So, criminals of all sorts are able to utilize the internet to organize whatever type of criminal activity that they want. With steganography, they can do it with a small chance of being discovered. This can create a bit of a problem regarding national security. Those that desire to protect our country can tap phones and follow around suspicious characters, but, if people are able to hide secret messages out in the open, how are the authorities supposed to discover them or even attempt to stop the delivery of the message. Pictures or movie or audio files can all be posted on websites or message boards or in chat rooms. With this medium of communication, people can relay information covertly over public channels and have little chance of being detected. Government agencies cannot possibly scan all these public channels searching for hidden messages. First of all, there are probably not a high volume of hidden messages, so a lot of the searches would prove fruitless. Also, even if they were looking at the right sites, how would they know that they found a hidden message since they are undetectable by the naked eye? Even if they did find the message, how could they know who the message was going to since it was placed in a

9 public viewing area where everyone can see it? So, it seems that such a public display of confidential information would be an almost ideal method of communication. It seems though this might have already caused problems with national security. It is suspected that the terrorists involved with the terrorist attack on September 11 th were using steganographic methods to communicate blueprints and sensitive information to coordinate their attacks. The New York Time reported in October of 2001 that the Al Qaeda used steganographic techniques to encode messages in images and then sent via or placed in public sites, with ebay being one of the mentioned sites. The pictures would seem completely harmless on ebay, but, this article claimed that there were messages hidden in the bits of these images. These claims were never confirmed, but some feel that they were an attempt by U.S. politicians to have an excuse to restrict the use of encryption and steganographic software. The problem is that it is difficult to detect. If the government had a way to detect such messages, they feel that they could prevent such tragedies from occurring. But, how would they begin to look for such hidden messages? Steganalysis is the art of discovering such messages. If the original file and the embedded file are both known, then the discrepancy between the two is noticeable and can be studied to reveal patterns of certain steganographic software tools. Acquiring these patterns can help to detect the use of the software on other files and discover hidden messages. But, with the original and the embedded message, it is still not always easy to find the patterns or signatures that are left by certain software methods of steganography. The most popular form of steganography in pictures is to change the least significant bits (LSB). This method of hiding data can be easily detectable with a

10 program that analyzes the different colors that are present. In digital pictures, the number of unique colors is not nearly as high as the number of pixels in the picture. The ratio of unique colors to number of pixels can be anywhere from 1:2 in a high quality picture to 1:6 in lower quality pictures. Many true-color images would thus have a very small color palette. Knowing this and that steganographic methods normally change the least significant bits, an altered picture can be analyzed showing a number of close colors. The occurrence of too many close colors would indicate that least significant bit encoding in the image. While the difference may be detectable to the naked eye with a side by side of the two images, it would not be easy to detect without the original. Therefore, to discover such LSB encoding in pictures, the pictures could be analyzed in such a manner. But, since these pictures would be placed in public places, all pictures in all public sites and boards would be subject to investigation and it is just not realistically possible to examine all the pictures on the internet. But, the whole point of steganography is to be undetectable. Being able to find patterns would defeat the entire purpose of hiding the message in this manner. So, methods exist that make it extremely difficult to detect without having the original, unaltered file. Sometimes, though, the existence of a hidden message is known even if it is not known in what form the message is. In this case, rather than trying to find and uncover the message, it may be easier to just attempt to destroy the contents of the message. This can be done by compression techniques which could possibly render the hidden data useless. But, this would be a violation of the people s right of freedom of speech, destroying our lines of communication. So, this is where the dilemma arises.

11 What is more important: the privilege of freedom of speech or national security and the safety of the country? III. Summary So, it seems there are the good and bad of steganography. The clear positive aspect of message hiding is the increased privacy that such a device can provide. An encrypted message hidden is a picture is more secure and harder to uncover than simply encrypting a message. While the message will be difficult to decrypt, it is clearly encrypted and could contain some secrets that people may want to uncover. But, an encrypted message hidden in a picture or a song is difficult to detect and then also difficult to decrypt even if detected. So, it adds that extra layer of protection and privacy to those who take advantage of it. On the other hand, it is another way for people to carry on illegal endeavors. With such methods to pass on information, secret communication can occur between criminals or terrorist groups that could threaten people s safety. Should steganography software continue to be allowed or should such practices be restricted to allow for a possibly safer environment? First of all, restricting a person s right to privacy seems like a direct violation of the first amendment, freedom of speech. This strikes at what is considered a basic human right. But, is it worth our safety? Even without steganographic software to hide messages, people who would feel some need to communicate covertly will find a way. There always seems to be another way. So, if the authorities attempted to stop steganography, some other way to secretly exchange messages will be developed.

12 While this sounds threatening, it is the truth. There will always be a demand for means of private communication, and steganography so far has been the most secure and effective method. The United States Constitution was created with the idea that government s power should be limited. The government s attempt to monitor peoples communications by installing backdoors into encryption and steganographic programs is a direct violation of this limitation of power since it infringes upon peoples rights for personal privacy. Even if the U.S. limited or banned the research or usage of steganography and cryptography, it would be used elsewhere throughout the world. In fact, I think it s safe to presume that the U.S. would fall behind in its research and development in these areas, drastically hurting and limiting our national security. Leaving steganography and cryptography open to the public s research and scrutiny is a good idea as the fields will continually grow in complexity and efficiency, and this way, even the U.S. will be able to benefit by staying in the front lines of research and development.

13 References Fridrich, J., R. Du and M. Long, "Steganalysis of LSB Encoding in Color Images", ICME 2000, New York City, July 31-August 2, New York, USA, Johnson, Neil F. ; Steganalysis - Attacks against Steganography and Watermarking Countermeasures ; Johnson, N. F. and S. Jajodia, "Steganalysis: The investigation of Hidden Information", IEEE Information Technology Conference, Syracuse, NY, USA, 1-3 September Petitcolas, Fabien A.P. ; the information hiding homepage digital watermarking & steganography; Radcliff, Deborah; Steganography: Hidden Data, Steganography. Symantec ; Steganography: High-Tech Hidden Messages ; April 30, 2002 ; Article 1314; Tran, Tu ; Steganography : The Art of Hiding Data ;