Keyword Alphabet

ACA Conventions are a good time to begin lifetime friendships with many people who have similar interests. They are also a wonderful opportunity to pick up a lot of information and education about cryptography. It is not coincidental that many of the Krewe solution scores have increased greatly with convention attendance.

Our ACA convention sites allow a great opportunity for ACA Krewe to plan their summer vacation setting. Conventions provide a great opportunity to get to know other members of the Young Tyros and adult members of the ACA and the cultivation of lifelong friendships.

In our last chapter, we related how most ciphers (disguised messages) are based on a key that allows both the sender and the receiver to communicate in ciphertext.

Here is a simple way to construct a substitution cipher alphabet with the use of a keyword. Pick a keyword that is easy to remember. Write the alphabet in a row of upper case letters. Write a keyword directly above it in lower case letters followed by the rest of the alphabet that does not appear in the keyword. We refer to this procedure as a Key 1 Alphabet.

zcipherabdfgjklmnogstuvwxy
ABCDEFGHIJKLMNOPQRSTUVWXYZ

You will notice that we begin our keyword over the upper case (ciphertext) letter ‘B’. If we had started our keyword above the upper case letter ‘A’, the lower case or plaintext letter ‘e’ would be substituted for by the upper case letter ‘E’ .

A letter may never be substituted for itself under ACA rules for simple substitution ciphers. When placing a plaintext keyword over the ciphertext alphabet, no identical letters may appear above or beneath each other. No letter may stand for itself (self-encryption).

A keyword may be started at any point over the ciphertext alphabet as long as it does not cause a letter to be substituted for itself.

It is equally important that duplicate letters in a keyword not be repeated, to avoid duplicate ciphertext letters standing for the same plaintext letter. Keeping these principles in mind, each keyword selected will produce different ciphertext.

The knowledge of this keyword between the sender and the receiver allows the disguised ciphertext to be converted to an easily read plaintext message. When this key is not provided the work of the cryptanalyst is ready to begin.

Indicate whether each keyword alphabet below is correct.

KW1. crazybdefghijklmnopgstuvwx
KW2. cipherabdfgjklmnogstuvwxyz
KW3. vwxyzcipherabdfgjklmnoqstu
KW4. uvwxcryptogrambdefhijklnqs
     ABCDEFGHIJKLMNOPQRSTUVWXYZ