Q: What is the book about?
A: Hiding information. Some algorithms disguise it by
giving it another form, others slip it into the noise of existing pictures,
documents, sound files or anything else.
Q: This is steganography?
A: Yes, some use that word and others call it "information
hiding". When the algorithms protect digital content, some people call
the result a "digital watermark". Most of the ideas do all of these things.
Q: These ideas are dangerous, right?
A: Some people are worried about them. After September
11th, many suggested that Osama bin Laden and other terrorists hid their
communications in images. Some suggested they were bundled in pictures
of junk for sale on Ebay. Others suggested it was hidden in porn. No one
has ever found any hard and fast evidence for such a thing, but it's certainly
in the realm of possibility.
Q: But the ideas are also useful?
A: All technology is neutral. The ideas are also very
useful to people who must protect digital versions of music and movies.
Creating these "digital watermarks" is one of the biggest challenges for
the companies selling content over the Internet.
Q: Is this the only application?
A: No, it's just the biggest. The list goes on. Practically
every application can benefit from the techniques. One paper at a conference
suggested that the algorithms could be used to "hide" a doctor's notes
inside an x-ray. The new file is instantly backward compatable. The old
software just sees an x-ray file, but the new software picks out the comments.
There's no need to redesign a database or purchase new software. This kind
of innovation is a crucial part of keeping health care costs reasonable.
Q: So anyone can use these techniques?
A: Sure, information is being "hidden" everytime
a programmer redesigns a new file format that holds new information while
remaining compatable with earlier versions. It may not seem like steganography,
but it is in the most abstract sense.
Q: Is steganography like cryptography?
A: It's a close cousin. Some steganography algoritihms
hide information so it can't be found. Others hide it with a key. If you
don't know the secret phrase or password, you can't get the information
Q: Why is the book called Disappearing Cryptography
A: When the first edition was published, the word "steganography"
was pretty uncommon. So we coined the title "Disappearing Cryptography."
It was meant to be both flashy and make a point. A few cryptographers don't
think that steganography can be secure. They don't understand how that
the categories blend together. Some stegonography algorithms are relatively
insecure, but others are just as secure as basic cryptography and
the output is in camoflage.