The Art Of Secret Writing:
Often there is a need to ensure that a message can only be read by those
it is intended for. Putting a letter into an envelope is the simplest way,
but does it really ensure this? Off course not! If intercepted, the envelope
may be opened. There are more sophisticated ways achieve the desired security
of a message: by hiding it so that it will only be recognized by the addressee
or by writing it in a way that it can only be understood by the addressee.
The first process is called steganography, the second cryptography.
This pages will deal with cryptography and only as far as required for
the use of CipherClerk's Applet. For more information I recommend the book The
Codebreakers - The Story Of Secret Writing by David Kahn.
The Virtual Envelope
Cryptographers take plain text and encipher it by using a
cipher into cipher text. A cipher is a general scheme for
converting one text into another one. Most ciphers use a key (a
word, a phrase or numbers) to specify how a general scheme is used. A plain
text is a text with the obvious meaning so that everyone can read and understand
it, while cipher text is not understandable unless you know - or find out
- which cipher and key was used. Cipher text is also called a cryptogram.
The reverse process, obtaining plain text from cipher text, is called to
Cryptanalysis attempts to obtain plain text without knowing
which cipher and key was used by decrypting the cipher text.
How Cryptograph Works
There are only two basic cryptographic algorithms for processing a text.
They are given along with a cryptogram of the phrase have fun:
Off course, transpositions and substitutions may both be used within a
single cipher. A code is a substitution, too. However, a substitution
cipher operates on single letters or on groups of - say 3 - letters,
while a code operates on words and / or phrases.
Transpositions rearrange it's letters: hfaeu vn
Substitutions replace it's letters: ibwf gvo
Usually only letters are processed by a cipher. In such a case numbers,
punctuation and other symbols in the plain text must either be spelled
out, encoded by letters or are removed from the plain text before enciphering
it. The cipher text is usually reformatted into groups of five letters.
How Cryptanalysis Works
Well, if you would like to learn more about this topic I recommend Cryptanalysis
by Helene F. Gaines. There is information on cryptanalysis on the web,
Cryptography on the web
Since there are a vast number of crypo-related sites on the web, I restrict
myself to the a single reference: The
Crypto Drop Box. Off course, all members of the CryptRing.
have exciting crypto related sites, too!
To proceed, you may