Hidden in Plain Sight: Technology, Art and Media in Steganography
by Eric Cruet

Introduction


Hiding information in plain sight or information hiding, is a generic term covering a wide range of issues dealing with embedding messages in media content. From this concept emanates steganography, a subset of cryptography, which is about the protection of messages. It is a term derived from the Greek, which literally means, “covered writing”. It is using art and technology to conceal communications. The actual existence of the message is concealed, as opposed to encryption, where everyone knows the message (information) is secret. Encryption deserves introduction. In encryption the message is not hidden in plain sight, but rather processed or “encoded” in the digital domain. It is important to make this distinction, since encryption has no effect on past, existing, or future analog media (unless digitized). From Regis Debray’s mediology perspective, it has a short chronology, evolves rapidly and is on pace with current IT (Information Technology), living in this unique digital world. Its currently relevant to Digital Rights Management (DRM) and its purpose in addressing Software Piracy, Intellectual Property and Copyright Protection issues. Furthermore, it attempts to keep pace with the ever-escalating cyberwar against hackers, rogue nation states, and the growing criminal Internet element.


There are some researchers who seem to think that the origin of steganography is biological or instinctual. There are examples where secret, inhibited methods of communications and action exist between animals. Beta males, when desiring to mate with females of Alpha males, attempt to do so in a surreptitious way (Kahn, 1996). The root metaphor, a term derived from philosophy, is a hiding place.


Media is essential to steganography. Humans have used a combination of technology, art and media to communicate, propagate and disseminate ulterior messages of various types. This essay begins by providing a historical perspective of hiding messages in plain sight, followed by the different types of media used to conceal them. It does not attempt to cover all media or all the technology. That would be the theme for a book publication.


As to what is covered, steganography can be used in a linguistic context. It can also appear as a covert channel in music, in art, or as a digital watermark. It is rapidly gaining use in social media to circumvent censorship and eavesdropping by undesired parties.


Let’s begin with a brief historical perspective on the subject.


I. Historical Perspectives in Steganography

There are some researchers who seem to think that the origin of steganography is biological or instinctual. There are examples where secret, inhibited methods of communications and action exist between animals. Beta males, when desiring to mate with females of Alpha males, attempt to do so in a surreptitious way (Kahn, 1996). The root metaphor, a term derived from philosophy, is a hiding place. My dog hides an extra treat he gets. People hide extra assets in safety deposit boxes.


Herodotus in Histories reported one of the 1st recorded instances of steganographyin 499 BC. Since he did not like living in Susa, he made plans to restore his power in Miletus by instigating a revolt. He shaved the head of his most trusted slave and tattooed a message on the scalp, then waited for the hair to grow back. Then he sent him as a messenger to Aristagoras with instructions to shave his head again as to reveal the message. He was to revolt against the Persians. Subsequently, Aristagoras followed Herodotus’ orders and burned the Persian city of Sardis.


Around same time, Herodotus also writes that Demeratus needed to advise Sparta about Xerxes’ plans to invade Greece. A hidden message was written on a wooden tablet that was meant to be covered in wax. After it was coated, the tablet for all practical purposes looked blank.


Other techniques were reported by Aineaias the Tactician, including messages hidden in the soles of shoes, women’s earrings, whitewashed wooden tablets and notes carried by pigeons.


The early Chinese use to write messages on thin strips of silk and encase the silk in balls of wax, called “la wan” then hide the balls of wax inside the body of the messenger.


Invisible inks were also popular and used to write between the lines of text by the ancient Romans. They were made of readily available substances such as urine, milk, and fruit juice. They would become legible when submitted to heat under a flame. Ovid was one of the 1st to use milk is invisible ink.


Finally, Johannes Trithemius (1462-1516), a German monk, and the author of Steganographia, was one of the 1st researchers of steganography and cryptography. His main piece of work developed what initially looked like magic and prophecy into systems that would hide messages in seemingly innocuous text.


Below is a copy of the cover of Trithemius’ Steganographia. Clicking on the book will take you to Google books where you can download a free eBook copy:





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Giovanni Porta, an Italian scientist born in 1535, contributed to steganography by concealing a message within a hard-boiled egg. He made ink by combining alum and vinegar and used it to write on the shell. This solution would penetrate the eggs shall and leave the message on the surface of the heart and egg which could revealed by cracking the shell open.
Lets now proceed to the individual treatment (deconstruction) of covert signals in media types.


II. Covert Signals in Language


Linguistic Steganography is the art of using written natural language to conceal messages. Many techniques have been used to accomplish this. Recently computer programs have been written to veil these messages within plain looking documents.

One of these programs is named NICETEXT. The primary goal of the software is to provide a system to transform ciphertext into text so looks like natural language at the same time retaining the ability to recover the original message. Although constructed for the English-language the methods and tools could be used for other languages. If you look hard enough, you can still find copies of downloadable copies of NICETEXT on the Internet.

The work was related to previous research done by Peter Weimar using statistical n-gram function algorithms. This mimics language functions probabilistically to hide message files in cover files. The problem with this approach, as well as with NICETEXT, is that the output is a far cry from the type of English that is used by real humans, and therefore arises suspicion.


III. Covert Signals in Textual Media

Cardano Grille System




The Cardano grille system is one of the safest ways to conceal a message if done correctly. Invented in 1550 and named after its creator, Gerolamo Cardano, it consists of a piece of paper at the hands of each recipient with several holes cut in it, called the grille. When you place the grille over a plain looking message and line it up its words, you reveal the hidden message. Illustration 3.1 provides an example:

Illustration 3.1:











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It is also claimed that the inscription beneath the bust of William Shakespeare is encoded with a Cardano Grille. This was the basis for the recent movie “Anonymous” which claims that Shakespeare never wrote a single word of his works.


IV. Covert Signals in Fabric Art

Civil War Rugs

In the Pre-Civil War era, it was illegal for slaves to read and write. So codes were a big part of the slaves’ existence and were used to chart their escape route, using what eventually became known as the Underground Railroad. Some forms of dance, spirituals, code words and phrases, and memorized symbols all allowed the slaves to communicate with each other on a level their white owners could not interpret. Codes were created and used by sympathetic whites, and by other Blacks. The Blacks included other slaves, former slaves or free men and women. In slavery, secrecy was one way the blacks could protect themselves from the whites; even the youngest child was taught to effectively keep a secret from anyone outside of the family.

Civil War rugs were used to send hidden messages to help slaves escape before the Civil War. The book Hidden in Plain View: A Secret Story of Quilts and the Underground Railroad, by Tobin et al., tells the story of the steganographic code that was used for generations.

The Underground Railroad was one of the main escape mechanism used by slaves to escape in the 1800s. Since quilts were hung outside to dry, they became an ideal way to communicate hidden messages. Special patterns would be sewn on them to relay directions or preparations to escapees who knew what to look for.

In this excerpt from Hidden in Plain View, an example is provided of the quilt coding:

The monkey wrench turns the wagon wheel towards Canada on the bear paw trail to the crossroads. Once they got to the crossroads they dug a log cabin on the ground. Shoofly told them to dress up, put on cotton and satin bow ties. Go to the cathedral church, get married, and exchange double wedding rings. Flying geese that stay on the drunkard’s path and follow the stars.

Below you will pictorials of the quilt symbols described in the excerpt:


Flying geese: A signal to follow the direction of the flying geese as they migrated north in the spring. Most slaves escaped during winter, and following the geese would guide them to water, food and rest.
flyinggeeseb.jpg


North star: A signal conveying two messages: prepare to escape and follow the North Star to Canada. This signal was also used in conjunction with music, specifically the song “Follow the Drinking Gourd”.


northstarb.jpg


Monkey Wrench: A signal to gather all the tools required for the fleeing slave’s journey, meaning the physical tools, as well as the mental and spiritual ones.



monkeywrenchb.jpg



Drunkard’s Path: A warning signal to take a zigzag route to elude pursuing slave hunters and their hounds that are in the area. A slave spotted travelling south, for instance, would not be suspected of escaping.


drunkardspathb.jpg



Dresden Wheel: It is possible that the Dresden Plate could be a variation of the Wagon Wheel. Records indicate that the Dresden Plate quilt pattern did not emerge until the 1920s.

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Characteristic of African culture is the communication of secrets through the use of common, everyday objects; the objects are seen so often they are no longer noticeable. This applied to the quilts and their patterns, stitching and knotting. It has been suggested that the stitching and the knotting on slave quilts contained secret information, too, as map routes and the distances between safe houses. Using the quilts, spirituals and code words, the slaves could effectively communicate nonverbally with each other and aid each other to escape.

There is some debate among researchers and scholars over the quilt code theory, and whether or not escaping slaves actually used codes concealed within quilt patterns to follow the escape routes of the Underground Railroad. As oral histories leave no written record, there is no written proof that the codes in the quilt patterns actually existed. What remains are the stories passed down through the generations from the slaves themselves, and, following the code of secrecy, many of the stories were never told.



V. Covert Signals Remixed in Music


Gaspar Schott (1608-1666), in his tome Schola Steganographica defined a technique for hiding messages by combining precise musical notes to letters of the Latin alphabet. The notes would not be pleasant to the ear if played, but to the untrained eye, it would appear as a normal musical score. Several centuries later, musical steganography would take its own identity. The music was very powerful, but the message not so clear.




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Back masking is the process of reversing an audio signal that originally played forward. When played normally the message will sound like gibberish, however, when the song is played in reverse the original message can be heard. Some of the first instances of reversed audio were the result of The Beatles’ experimentation during the recording of Revolver. Since then, back masked messages have turned up in all kinds of music with messages ranging from humorous to satanic. Today, reversing audio is a popular way to censor explicit words for radio. This is a form of steganography, although in this case, the intended audience or the motivations of the transmitter are not clear, and perhaps, will never be known.

Here are some examples:

Queen: Another One Bites the Dust


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In the early 1980’s, Queen was accused of hiding a reversed message in their song “Another One Bites the Dust”. Christian evangelists claimed that when played in reverse the lyrics “another one bites the dust” become “It’s fun to smoke marijuana”. Some believed since the song had other strange effects on it, it was possible the band had purposely used back masking to hide the pro-marijuana message. A spokesperson for Hollywood Records denied that the song contained a hidden message. The message is widely considered to be unintended. Many cite this song as an example of phonetic reversal, where a word when reversed, sounds like another word.

Led Zeppelin: Stairway to Heaven


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In January 1982, Paul Crouch accused many rock artists of hiding messages in their songs through back masking. One example he pointed out was the Led Zeppelin song “Stairway to Heaven”. When played normally one hears: 
“If there’s a bustle in your hedgerow, don’t be alarmed now
It’s just a spring clean for the May queen
Yes, there are two paths you can go by, but in the long run
There’s still time to change the road you’re on”
When played in reverse Crouch said a satanic message could be heard: 
“Oh here’s to my sweet Satan. 
The one whose little path would make me sad, whose power is Satan. 
He will give those with him 666.
There was a little tool shed where he made us suffer, sad Satan.”

The band ignored these claims, however Swan Song Records issued a statement saying “Our turntables only play in one direction…forwards”. The alleged satanic message has become, arguably, the most famous instance of back masking, adding to the mystery and legacy of Led Zeppelin. Many however, say it’s merely a coincidence, and is simply another case of phonetic reversal.

VI. Covert Signals in Digital Media


Digital Watermarking

There are 2 kinds of digital watermarks: visible and invisible. The concept behind a visible watermark is to superimpose a digital logo, similar to the digital mark eBay places on the pictures for the items you submit for sale. Another example would be the superimposed image of “ESPN” on the lower right-hand corner of the television screen when you are tuned to that channel.

An invisible digital watermark however requires complex signal processing. But the most common example would be the invisible watermark found that a $20 bill. If you look at the side with the portrait of Pres. Andrew Jackson you will see the portrait is echoed with a watermark on the right. This watermark is not only invisible during normal use but also carries information about the object; in this case the authenticity of the bill (Cox, Miller, Bloom, 2002).

A digital watermark used by Disney can also serve as a digital fingerprint. While a movie might have the watermark “Property of Pixar” in order to verify its legitimacy, the digital fingerprint could be also be imprinted on the movie at the time of purchase and include details such as the date and the retail location where it was purchased. Even though the security scheme might eventually be defeated, the developers of the technology will continue to work on making future systems that are harder to break.

VII. Covert Signals in Social Media

A. Social Steganography among Teens

Although many parents feel they have good relationships with their teenage children, sometimes they don't understand the social protocols on Facebook. Nowadays both have Facebook accounts. Both parents and kids get frustrated specially when, for example, mom posts on her daughter's account. Most of the time the result is that her daughter's friends “disappear for a while” to quote someone interviewed for this essay. Gloria, her name for the remainder of the interview, claims that it's uncool having her mom or dad posting frequently on her wall. She knows they have good intentions however she feels negative peer pressure. “It's just plain uncool for mom to be constantly checking my Facebook account”. In order to avoid her mother's overreaction Gloria will avoid posting things that have potential for misinterpretation. This has caused teens on FB (Facebook) to develop a coded language to hide messages state steganographically.

For instance, when Gloria broke up with her boyfriend she was depressed. When her mother found out she concerned. Normally she would have posted the lyrics to a song that were representative of her mood. However she was worried about what her mom might think. So instead of posting the depressing lyrics, she posted lyrics from Monty Python's “Always Look on the Bright Side of Life”. This worked ok. Her mother posted that she was happy she got over the breakup quickly. On the other hand, her friends knew that this song appears in a section of the movie when the characters are about to get killed. So they made sure they reached out to her to see how she was feeling.

It's interesting to note how the most popular social media websites today can be used to represent hidden meanings in messages regarding social functions of politics, ideology, and personal feelings. This will become more apparent as we move to the issue of social steganography in China.

B. Social Steganography in China

For the young Chinese, living publicly in the social sphere often requires knowing how to say one thing, concealed within another. In the current digital and social media space, it's becoming increasingly important to strike a calculated balance between what is private in what is public, in other words, appropriate for the public. This makes stenography a useful tactic for communicating with a broader audience. It is no secret that Internet censorship in the People's Republic of China is conducted under a wide variety of laws and administrative regulations. In fact more than 60 Internet regulations having created by the government and implemented by the provincial branches of state owned ISPs (Internet service providers). This makes it uniquely challenging for those living in China to communicate openly within the nation as well as outside the country.

In this TED video, Michael Anti, a veteran Chinese blogger, talks about how to get around censorship:

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Chinese loggers use number strings in alternating sequence with a numeric identifier so it can be embedded with ease and thereby fool the censorship filters. For instance, they refer to the date of the Tiananmen Square Massacre as 6489 (June 4, 1989). To defeat the filter it’s encoded as June 1234, 3149683659.

In addition to using song lyrics and the use of coded words associated with the social steganography used by teens described previously, they also prefer to use Sina Weibo, a hybrid micro blogging website which allows the posting of short messages akin to Twitter. The brief texts lend themselves to encoding hidden plaintext between the Chinese symbols in each message.

VIII. Interpretations

A steganographic object, that is, the composite of the hidden message and the medium used to hide it covertly, is intended as a meaningless object from a cryptographic point of view. By definition, a cryptogram exists if and only if its meaning can be inferred by means of a decryption routine. So a stego-object has to appear safe in every respect in order to carry meaning. This is another function that is necessary and relevant for the media: transparency with respect to the message. One the media has been chosen for cover and the meaning has been hidden, the stego-object moves from the sphere of cryptology to steganography and moves into a semantic dimension.

The use of musical scores by Gaspar Schott, the system by Johannes Trithemius for generating pseudo-logical texts, and the use in World War II by prisoners of war to convey Morse code messages by using the dots in the letters “i and j” and dashes in letters “f and t” are all indicative of one thing: the use of the covert channel by a pre-conceived arrangement of the transmitter(s) and the receiver(s).

This agreement between parties is what gives steganography its raison d'être. Nobody would have noticed the hidden image in the “Magic Eye” prints connected to the Graphics Design scene of the 90s, first displayed in the magazine Ray Gun, unless told by the artists to look closely at them? What would otherwise look like a poster hides textual information totally unrelated to the art, and medium.

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Although the use of steganography initially was aimed as an alternative to cryptography, new scientific advances have positioned it as one answer to the problem of copyright and intellectual property for digital media. Newer techniques can be used to stealthily identify the owner or distributor of the source. What makes it attractive in lieu of encryption is that once encryption is removed you lose control over dissemination of the data.

Digital watermarking has been another of the few available techniques that have attempted to dealing with copyright issues. Although it still confronts technical hurdles, there are no other technologies at the ready to substitute it. However the issues of Piracy, Copyright, and Intellectual Property go far beyond any type of cryptological solution. The model of content protection and distribution will have to change in order to meet the changes in technology, culture, and demand.



Next time you have to keep a message secret, ask yourself this question:

Why use covert signals to hide the information?

It takes creativity, ingenuity, and artistry to create hidden meanings.

Because the message is fleeting, the technology temporary, and function in an attempt to exceed form, might or might not accomplish its purpose.

The significance is fleeting, but the artistic medium perseveres.


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References:


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  2. Cox, I. J., Bloom, M. L., & Miller, J. A. (2002). Digital Watermarking. London, United Kingdom: Academic Press.
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  4. Owens, M. (2002). A discussion of covert channels and steganography. SANS Institute.
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  7. Tobin, J. L., & Dobard, R. G. (2000). Hidden in plain view: A secret story of quilts and the Underground Railroad. Anchor.
  8. Boyd, D. (2010, August 23). Social Steganography: Learning to Hide in Plain Sight. In DML Central: digital media and learning - the power of participation. Retrieved December 13, 2012