Cracking Codes: Part II

Not too long ago, we posted a little how-to on Substitution Ciphers, and now we’re moving on to Keyword Number Ciphers. If you need a little refresher before Part II, be sure to check out Cracking Codes: Part I.

Keyword Number Ciphers:

Most criminal use ciphers to hide numbers, especially telephone numbers, addresses, weights, and money amounts (doesn’t take a wiz kid to figure out why, hey?). Keyword number ciphers are the most common system for encrypting numbers and are used in the same manner as keyword alphabet ciphers (see Part I). Normally the keywords involved are ten-letter words with no repeat letters.

Plain Text:         1     2     3     4      5      6      7     8     9      0
Cipher Text:      B     L     A     C     K     H     O     R     S     E

Foreign language keywords are often used. The following is an example of a drug ledger that used a Spanish keyword cipher:

Enciphered Drug Ledger

While decrypting the cipher, the cryptanalyst made the initial assumption that the letters represented numbers. If A+A+A = A, as set forth on the right-hand column, then A must equal 0 or 5. Using the same logic, if A+Q+Q = A, then Q must equal 5 and A must be 0. The cryptanalyst continued until he was able to establish the following relationships:

Plain Text:        0     1      2     3     4      5      6     7     8     9
Cipher Text:     A     T     S                    Q     R     O           M

Further analysis of other cipher text and anagramming the cipher text letters into an intelligible word revealed the following reverse order key:

(“my orchestra” in Spanish)
Plain Text:         9     8     7      6      5      4     3     2     1     0
Cipher Text:     M     I     O     R     Q     U     E     S     T     A

You’re all over it? Not so fast – number ciphers do not always use a keyword. An drug dealer in an Arizona prison sent a letter to a cohort instructing her to mail a shipment of drugs to the following Georgia address:

GCDI Abercorn Drive
Savannah, GA 31206


Don’t despair! Note that the cipher text letters are all within the first nine letters of the alphabet. If A is assumed to equal 0, then the following key results:

Plain Text:        0     1      2      3     4     5      6      7     8     9
Cipher Text:     A     B     C     D     E     F     G     H     I     J

The key can be verified by checking the resulting street address. If the key turns out to be invalid, you can try moving the 0 to the end of the number series and assume that A = 1 instead. In this example, the first assumption was actually correct. A tiny notation “A = 0” was found in the lower right-hand corner of the prison letter, confirming the key. Not too smart having the answer to cracking the code and the coded letter all on the same piece of paper, was it?

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