Steganography means hiding information in or on something in such a way that a non-initiated person is unaware of the existence of the information. Almost anything can be used as a carrier medium, even people: in ancient times, slaves had their heads shaved, something was tattooed on them and when the hair had grown back, they were sent off as living “data carriers”. But steganography is also classic agent methods such as secret ink or the false bottom in packages or suitcases, hollow heels in shoes and the use of microdots. More relevant for geocachers is linguistic steganography, i.e. the hiding of text in a text (for example via keywords with special meanings) or that of information in a picture (optically: for example via blades of grass as Morse code) or computer-aided with appropriate software.

The disadvantage of these methods, which are actually pretty, is that the sender and receiver have to exchange information about the type of hiding place(s). And this is also the big disadvantage when computer-assisted steganography is used in (geocaching) puzzles: the puzzler should have at least a rough idea whether something has been hidden here, and if so, with which tool, because trying through all the usual or unusual suspects, sometimes with (various) password possibilities, results in an almost endless and, above all, rather boring search for the coordinate. After all, something that has been hidden with steganography software can only ever be retrieved exactly with it.

If you ever come across a listing where there is no way to find the coordinates, but which contains a file, usually a picture, but possibly also an mp3 file, a video or an unknown type of file, which the owner has stored on his own web space, then a closer examination of this file could help. Is this file larger in terms of data volume than it typically should be? Then another one could be hidden in it. If it is an image and the image is unusually large (I am referring to the number of pixels), there could be something hidden visually that can perhaps only be seen in full image size. I once found strange looking dots on a door frame in a nice black and white drawing at full resolution. A web search revealed that the original image did not have them. The solution was then simple counting to get the east and north minutes.

If it is a JPG image with possible computer-assisted steganography, I always examine it first with the small, ancient software “stegdetect”. However, this is a command line tool (“stegdetect -t p filename.jpg”). Even if stegdetect cannot recognise which tool has been used to hide the file, it often gives at least a hint as to whether the JGP has been manipulated at all. I have also received similarly clear indications with other steganography software. Once steghide reported that something was wrong with a BMP file that had been encrypted with a completely different software, namely Grafik-Key. At least from then on I was sure that I was on the right track, namely the steganography track.

At this point, there is not much left for me to write other than a simple (and by no means exhaustive) list of more or less common steganography programs and the types of data they can encrypt. If the software offers the possibility of passwords, the GC code of the listing, the name of the owner, the cache or something that clearly stands out in the text is a good candidate. Alternatively, the filename.

Good luck finding hidden information, for example, with:

• stegano.net (JPG, PNG)
• Carmouflage (rather outdated, runs in the free Windows version only up to Windows XP)
• steghide (image and audio files)
• Grafik-Key (BMP)
• steganog (BMP)
• Openstego
• OpenPuff (images, Audio, Video, Flash)
• JPHS (Audio, Video, Images, Text)
• Outguess (JPG)
• data-stash
• silent eye
• GpgSX 0. 67b
• Stealth Files 4. 0 (various file types EXE-, DLL-, OCX-, COM-, JPG-, GIF-, ART-, MP3-, AVI-,WAV-, DOC-, BMP- and WMF-files )
• PGE – Pretty Good Envelope
• S-Tools 4.0 (doesn’t seem to exist free on the web anymore? )
• F5 (doesn’t seem to exist free on the web anymore?)
• mp3stego
• Snow – hides data in ASCII text, more precisely in its spaces
• spammimic encrypts text into something that looks like spam

Even the current freeware encryption market leader TrueCrypt offers a form of steganography. Not only can you simply encrypt files or drives with it, you can create a “hidden container” in them that you only find out exists if you enter the right password. There is one for the “normal” container and another for the steganographically hidden “hidden container”. Encryption and hiding in one. Less something for geocaching mysteries, but definitely something for people who do have something to hide. (Addendum from 23.12.2014: truecrypt has since discontinued its services. Rumour has it that the US government forced a backdoor into this software. Truecrypt is therefore no longer secure. Its successor, which is considered secure again, is called VeraCrypt. )

And finally, a know-it-all for future puzzle-owners: actually, computer-based steganography puzzles do not conform to GC guidelines, since you have to install software to decrypt them.