Cryptography Reference
In-Depth Information
data to disguise its origins and obscure its destination. It is about
submerging a conversation in a flowof noise so that no one can know
if a conversation exists at all. It is about taking your being, dissolving
it into nothingness, and then pulling it out of the nothingness so it
can live again.
Traditional cryptography succeeds by locking up a message in
a mathematical safe. Hiding the information so it can't be found
is a similar but often distinct process often called
steganography
.
There are many historical examples of it including hidden compart-
ments, mechanical systems like microdots, or burst transmissions,
that make the message hard to find. Other techniques like encod-
ing the message in the first letters of words disguise the content and
make it look like something else. All of these have been used again
and again.
David Kahn's
Codebreakers
provides
a good history of the
techniques.[Kah67]
Digital information offers wonderful opportunities to not only
hide information, but also to develop a general theoretical frame-
work for hiding the data. It is possible to describe general algorithms
and make some statements about how hard it will be for someone
who doesn't know the key to find the data. Some algorithms offer a
good model of their strength. Others offer none.
Some of the algorithms for hiding information use keys that con-
trol how they behave. Some of the algorithms in this topic hide in-
formation in such way that it is impossible to recover the informa-
tion without knowing the key. That sounds like cryptography, even
though it is accomplished at the same time as cloaking the informa-
tion in a masquerade.
Is it better to think of these algorithms as “cryptography” or as
“steganography”? Drawing a line between the two is both arbitrary
and dangerously confusing. Most good cryptographic tools also pro-
duce data that looks almost perfectly random. You might say that
they are trying to hide the information by disguising it as random
noise. On the other hand, many steganographic algorithms are not
trivial to break even after you learn that there is hidden data to find.
Placing an algorithm in one camp often means forgetting why it
could exist in the other. The best solution is to think of this topic as a
collection of tools for massaging data. Each tool offers some amount
of misdirection and some amount of security. The user can combine
anumberofdifferenttoolstoachievetheirend.
The topic is published under the title of “Disappearing Cryptog-
raphy” for the reason that few people knew about the word “stegano-
graphy” when it appeared. I have kept the title for many of the same
practical reasons, but this doesn't mean that title is just cute mecha-
nism for giving the buyer a cover text they can use to judge the topic.
