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Is It Ciphers or Cyphers?
Ciphers, also spelled "cyphers," are the same as
"codes" in common usage. However, there is a technical
distinction used by cryptographers. A code is something that
works at the level of meaning. In a coded message, for example,
"big daddy" might refer to a person or a boat, or anything
else. An otherwise meaningless string of letters or numbers,
like "wwx23" could represent a word or a whole phrase,
such as, "Meet me at the usual place." (Because of
this, codes can actually shrink the length of a message, or the
space and time needed to create it.)
A cipher (or cypher), on the other hand, works at the level
of individual letters or at least small groups of letters, or
even bits of information in the case of modern computer encryption.
A simple substitution cipher, for example, might replace each
letter with a two-digit number (a=11, b=47, etc.). Using both
ciphers and codes in the same system makes messages even harder
to decipher.
The problem with codes is that they can require a large and
ever growing code book that both the sender and receiver of secrets
messages must have. Some cryptographers also argue that coded
messages are ultimately easier to decode or decipher than messages
based on a good cipher. Ciphers, rather than codes, have become
the dominant method of encryption in modern cryptography.
(Cryptography is "The process or skill of communicating
in or deciphering secret writings or ciphers.")
Creating A Cipher
A couple more definitions: A cipher (or cypher) is essentially
an algorithm - a procedure for enciphering (encrypting) and deciphering
(decrypting) information or messages. The encrypted message -
sometimes called "scrambled", is referred to as "ciphertext".
The decrypted message is referred to as "plaintext"
(after it has been "unscrambled"). Ideally, good codes
or ciphers should be "unbreakable", meaning they are
impossible to decipher without having the key.
What is the key? If the cipher uses simple letter substitution,
the key may simply be a chart showing which letter represents
which: a=d, b=t, c=f, etc. However, a key may also be a bit of
information that determines which algorithm is used. For example,
a system may use twenty different letter-substitution ciphers,
but which one is used may change at every fourth letter. The
number "4" could be the key telling the receiver the
frequency of the changes.
In a more complicate scheme, even the frequency of the changes
may change. For example, suppose a sender and receiver each have
the same list of ten different letter-substitution ciphers. A
key might be sent separately from a message, or encoded in a
different way in the message, and consist of a string of digits;
for example, "3468". This key could tell the receiver
to change the cipher used after 3 letters, and again after 4
letters, and again after 6 letters, and again after 8 letters,
and again after 3 letters, and so on.
The receiver works his way down the list of ciphers, changing
to the next one at each position indicated by the key. As you
can imagine, analyzing letter frequency - one of the traditional
ways of breaking codes, as outlined on the page, Code
Breaking - wouldn't be very helpful here. Without the key,
even a message using such simple letter-substitution ciphers
can be very difficult to decipher.
Note: To see a message written using a simple cypher
(a cryptogram), visit the page, "Code
Breaking," or for the cryptogram and the solution, go
straight to the page, "More on
How to Break Codes." For more on ciphers, you can also
visit the page, "Cryptograms."
All the pages on codes, ciphers and cryptograms are listed
on the page: Secret Codes.
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