The Keyword Alphabet as a Solving Tool

It is not coincidental that many of the ACA top constructors (those are the devious Krewe members who send in diabolical ciphers to the Cm) are also among the ACA top solvers.

Cipher construction is one of the best ways of learning deciphering skills. Learning construction principles breeds familiarity with the makeup of cipher types and means to their solution.

In Chapter Eight, we spoke of using a Keyword Alphabet as a tool for the construction of a cipher. This chapter we’ll show how that very same Keyword Alphabet tool can be so helpful in the solving process. Take a look at a random ciphertext to plaintext letter simple substitution cipher that uses every letter of the English alphabet (pangram):

BXJ CQLWZ NAGSV PGD OQUEF GHJA T ITRK YGM
The quick brown fox jumps over a lazy dog.
Plaintext –  rtqxpsovleyigbjfuzwamnchdk
CIPHERTEXT - ABCDEFGHIJKLMNOPQRSTUVWXYZ

In her work, Cryptogram, A Pleasant Diversion, Jude Patterson, (JUDE) describes the random assignment of substitution letters as “alphabet soup.” It serves little useful purpose between the author of a ciphered message (cryptographer) and the receiver. Keep in mind that the original purpose of the cryptogram or disguised message is to send a secret message. If a message is constructed with a random alphabet, it becomes much more difficult for the recipient to read the message.

Keyword Alphabet Uses.

The keyword alphabet has two distinct purposes:

  1. Ease of cipher construction – Keyword alphabets  are easily followed and repetition of the use of the same ciphertext letter for more than one  plaintext letter is more easily avoided.
  2. Ease of message interpretation – A disguised message is easily read when the reader has the keyword used to construct the message.

Let’s discuss two of the keyword alphabets used in simple substitution ciphers. Description of these can be found in The ACA and You Handbook, P26

K1 Keyword Alphabet Keyword “cipher

In the K1 keyword alphabet, the plaintext alphabet contains the key. The ciphertext alphabet is normal.

Plaintext –    abdfgcipherjklmnoqstuvwxyz
CIPHERTEXT –   DEFGHIJKLMNOPQRSTUVWXYZABC

Plaintext alphabet contains the key. (cipher)

  • Ciphertext alphabet is normal.
  • Each alphabet must contain 26 letters.
  • Duplicate letters in the keyword are excluded.
  • No ciphertext letter may represent more than one plaintext letter
  • No ciphertext letter may represent the same plaintext letter (no self-encryption).

We begin the ciphertext alphabet above with the letter “D” because starting the alphabet with either A, B or C will result in a self-encrypted letter. (Test it.)

K2 Keyword Alphabet Keyword, “HAPPYDAYS.”

Plaintext –  abcdefghijklmnopqrstuvwxyz
CIPHERTEXT – HAPYDSBCEFGIJKLMNOQRTUVWXZ
  • Ciphertext alphabet contains the key.
  • Plaintext alphabet is normal.
  • Each alphabet must contain 26 letters.
  • Duplicate letters in the keyword are excluded.
  • No ciphertext letter may represent more than one plaintext letter.
  • No ciphertext letter may represent the same plaintext letter (no self-encryption).

The keyword(s), HAPPYDAYS, appears as HAPYDS in the ciphertext alphabet with its duplicate letters suppressed. We may begin the keyword(s) at any letter under the plaintext as long as we are careful not to have a letter represent itself.

Key word alphabets are the tools used by the senders and receivers of secret messages for ease of reading a disguised message. An agreed upon keyword eliminates the need for any cryptanalysis.  In a future column, we will examine how keyword alphabets can also aid the solving process for the non-possessor of the keyword (cryptanalyst).

K2 Alphabet Construction

Let’s use the same keyword alphabet as Chapter Eight with the keyword, “CIPHER.”

Plaintext -  abcdefghijklmnopqrstuvwxyz
CIPHERTEXT - XYZCIPHERABDFGJKLMNOQSTUVW
KW-1. Aristocrat. It's easy. K2 (32)    (SNEPA)     LIONEL
RO  RN  IXNV  OJ  TMROI   XGC  NIGC   CRNHQRNIC FINNXHIN.

Apply the principles that you have learned to convert the Caesar crib (SNEPA) into plaintext and begin designing a K2 Keyword Alphabet.

Look at what happens when we post the CIPHERTEXT letters under the plaintext letters (write) in the K2 Alphabet:

abcdefghijklmnopqrstuvwxyz
    I   R        M O  T

Our Caesar shift has provided us with CIPHERTEXT letters TMROI equaling the plaintext letters “write.” The spacing of TMROI in the CIPHERTEXT alphabet tells us that N must equal s and that two of the CIPHERTEXT letters PQS must fall between CIPHERTEXT letters O and T. (R is on the left hand side of the alphabet slide and we know it to be in the keyword.)

We can also make very good educated guesses on the plaintext letters represented by CIPHERTEXT letters, UVWXYZ, because of their location in the alphabet to CIPHERTEXT letter T.

This is an example of how the Keyword Alphabet can be helpful in generating additional plaintext letters. It is an invaluable tool to the deciphering process. It is a good habit to post the Keyword Alphabet simultaneously to the solving of the cipher to gain maximum insight to more plaintext. Pen or pencil known letters in red.

Continue the process through to completion for the KW Ciphers below.

Keyword Alphabet Quiz

KW-1. Generate K-1 Aristocrat plaintext.

KW-2. Identify Keyword Alphabet used.

KW-3. The Caesar shift used was equal to?

KW-4. The keyword Alphabet will be automatically complete after solving the cipher.

True or false?

Keyword Alphabet Review

1) abcdefghijklmnopqrstuvwxyz
   CIPHER
    CIPHER
          CIPHER
               CIPHER

2) abcdefghijklmnopqrstuvwxyz
           PETUNIA

3) abcdefghijklmnopqrstuvwxyz
   JMNOPQRSTVWXZL CK ABDEFGHI

Keyword Alphabet Review Quiz

KW-5. What is the correct placement of the keyword CIPHER above?

KW-6. Complete the 2nd keyword alphabet.

KW-7. What is the keyword in the 3rd keyword alphabet?

KW-8. True or False – All of the below statements are true.

  1. Keywords are used in many different cipher types.
  2. Keywords provide ease of communication between the sender and receiver.
  3. Self-encryption allows a letter to be substituted for itself.
  4. ACA practices do not allow for self-encryption.
  5. The cryptanalyst’s work begins in the absence of a keyword.