Numbered Key

History

First published in the May-Jun 2010 edition of American Cryptogram Association (ACA) magazine The Cryptogram the Numbered Key cipher is a substitution cipher introduced by ACA member BION. It uses numbers to represent plaintext letters and is similar to the Homophonic cipher but with plaintext letters being replaced by more than one ciphertext number, usually with the more common letters being replaced by more ciphertext numbers.

Description

The cipher is constructed by creating a key from a short sentence, phrase or word. This is extended to include missing letters of the alphabet which are added to the phrase. The length of the key can vary but is not less than 26 letters.

For example using the key phrase "You will never win if you never begin" and inserting this into the middle of the missing letters the keyed alphabet becomes JKMPQSTXZYOUWILLNEVERWINIFYOUNEVERBEGINACDH. Numbers are then assigned to the keyed alphabet starting with 00, 01, 02... to the end forming the numbered key. This can be represented in a table:

0123456789

0 JKMPQSTXZY

1 OUWILLNEVE

2 RWINIFYOUN

3 EVERBEGINA

4 CDH

This numbered key is used to encipher the plaintext. The word YESTERDAY would be enciphered as:

Plaintext: y e s t e r d a y

Ciphertext: 09 32 05 06 17 33 41 39 09

Example

Key phrase: You will never win if you never begin

Plaintext: Any kid will run any errand for you, if you ask at bedtime.

Plaintext: a n y k i d w i l l r u n a n y e r r a n d

Ciphertext: 39 29 09 01 37 41 21 22 15 15 20 28 38 39 16 26 17 20 33 39 23 41

Plaintext: f o r y o u i f y o u a s k a t b e d t i m e

Ciphertext: 25 10 33 26 27 28 24 25 09 27 28 39 05 01 39 06 34 19 41 06 22 02 17

Ciphertext: 39 29 09 01 37 41 21 22 15 15 20 28 38 39 16 26 17 20 33 39 23 41 25 10 33 26 27 28 24 25 09 27 28 39 05 01 39 06 34 19 41 06 22 02 17

Solving

Solving methods: Hill Climbing search.

Only numbers in the range 00-99 are used where each number replaces a single letter.

The Numbered Key cipher type enables a crib to be included when solving with a dictionary search. This is optional but including a crib can improve the solving speed.

On selecting the Solve button a dialog box below will appear to enable the crib and crib location to be set. On selecting OK, the program will search for a solution.

Crib – Enter the crib in the Crib field. Spaces and punctuation will be ignored. A long crib will improve the searching speed.

Only show locations containing repeated pairs – Selecting this option will limit the number of possible crib locations to only include those where the ciphertext pair of numbers is repeated, possibly making it easier to locate the crib.

Click on the Locate crib button to populate the Crib location list with possible locations for the crib.

Crib location – Select the location of the crib from the list then press OK. When a crib location is selected the ciphertext and plaintext positions are shown below the Crib location confirming the location selected.

The crib location within the cipher will also be displayed in the Addition crib location textbox along with any other letters resulting from the crib. In this textbox additional plaintext can be entered to help improve the solution.

Click OK to start searching for a solution.

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