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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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