Puzzle Solving 101: Lesson 8: Steganography
This is the eighth in a nine part series originally written and published by ePeterso2 as part of his Puzzle Solving 101 Cache Series. Reprinted here with permission of the author. Minor edits have been made by Skottikus to apply this lesson to the Kingston Geocaching Area.
The first nine caches in this series will help you build your puzzle-solving skills. Each one contains a lesson focusing on a specific skill, examples of how to use that skill, an exercise to test that skill, and a cache (in Florida) to find as a reward. Study the lesson, complete the exercise, and you'll find the location of a geocache. Save your answers as they can be used to solve a special remote solver TB from here in Kingston as well!
This series of caches has discussed a number of different types of puzzles commonly used to hide geocaches. But some of the most difficult-to-solve puzzles are created using a method known as steganography. Steganography means literally "hidden writing". It is similar to cryptography in that it is used to send a message so that only the intended receiver can make sense of it.
Whereas the purpose of cryptography is to scramble a message into unintelligible gibberish, the purpose of steganography is to keep unintended recipients from discovering that a message even exists at all.
A steganographic message appears to be something else, typically something common and innocuous. A message can be a letter, an article, a shopping list, a photograph, an audio recording, or some other form. This apparent message is called the covertext. To create a steganographic message, the plaintext is typically encrypted in some manner using a cipher to create the ciphertext. This ciphertext is then embedded into the covertext to create the stegotext. The stegotext is often surrounded with nulls, which are extra pieces of information not part of the hidden message but which are included to increase confusion and distraction for those seeking the message.
Probably the best way to understand this process is with some examples:
- One of the most well-known steganographic tools is invisible ink. A secret message may be written in invisible ink over top of the cover text; to read it, the recipient would hold the cover text up to a particular shade or intensity of light. (Remember the opening scenes of The DaVinci Code?)
- In ancient Greece, wooden tablets covered with layers of wax were often used as the medium for writing messages. A secret message could be hidden by writing the message directly on the wood before covering it with wax. The recipient would then simply melt the wax to read the message.
- Also in ancient Greece, Herodotus tells the story of a message tattooed on a slave's shaved head, hidden by the growth of his hair, and exposed by shaving his head again. The message allegedly carried a warning to Greece about Persian invasion plans.
- During World War II, a spy for the Japanese in New York City, Velvalee Dickinson, sent information to accommodation addresses in neutral South America. She was a dealer in dolls, and her letters discussed how many of this or that doll to ship. The stegotext in this case was the doll orders; the 'plaintext' being concealed was itself a codetext giving information about ship movements, etc.
- Digital image files can be used to conceal information. For example, the image on the left is the stegotext; the image on the right is the hidden message. (The cleartext is in the two least-significant bits of the color level of each pixel in the stegotext. Don't worry if you don't know what that means ... just appreciate that the picture of the cat really is hidden inside the picture of the trees.)
Unfortunately, due to the extremely wide variety of methods that can be used to encode information, there is no easily generalized method of performing steganalysis. This is why these categories of puzzles can be so infuriating. Here are some places to look for clues:
- Look in the body of the stegotext. It may have clues that indicate the type of information contained. Things in the stegotext that seem odd, inexplicable, or otherwise out of place (no matter how slightly) may also be indicators that they hold the key to the secret information.
- Look inside the digital message. Executable, image, and audio files often have methods of including information that describes the contents of the file that are not directly part of the content of the file. For instance, an MP3 file can contain the name of the song, artist, and album, although none of those things changes the audio playback of the file. A secret message could be hidden in any of the extra fields of such a file.
- Get to know the sender and the receiver. Knowing something about the individuals transmitting and receiving the message may uncover information about how to decrypt the message.
- Use the tactics described in Lesson 2 of this series to find clues. Look for things that may hold patterns of coordinates or clues to container sizes or hints as to hiding spots. Especially watch for things that fit into some kind of overall repetitive pattern.
Think you paid attention in class? Try Exercise 8 found at GCYXZ8 Puzzle Solving 101 - Lesson 8: Steganography.
Save your answer...it will be important later...