Solved 408-character cipher

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Information, Analysis, Experiments

Last 18 symbols of the 408 cipher

The last 18 letters of the decrypted plaintext are gibberish when using the same key that is used to decrypt the rest of the plaintext. What are the explanations for this?

  • Possibility: The symbols were pulled down from symbols above the last row of the cipher text.
    • Glurk's original proposal. There is good support for this explanation.
    • Columnar repetition experiment. This tests how often random selections of the last 18 symbols would "accidentally" produce the same number of columnar repetitions (12) that we see in the original 408 cipher.
    • Second experiment which includes repeated tetragram. This tests how often random selections of the last 18 symbols would "accidentally" produce the same number of columnar repetitions (12), where a tetragram repeats in the same column.
    • Combinatorial calculation. This is a calculation of the probability that random selection of the last 18 symbols would produce columnar repetitions that are observed in the unmodified 408 cipher.
  • Possibility: A plaintext message is encoded somewhere in the last 18 symbols, using some other system of encipherment.

Homophone sequences

  • Homophone sequences - Several plaintext letters are assigned multiple homophones (ciphertext symbols) to conceal the language frequencies of the plaintext message. This page enumerates the sequences in which these homophones appear in the original ciphertext. What was the scheme used by the killer to select from the multiple homophones?
  • Nick Pelling's articles on homophone sequences. Part 1 | Part 2
  • John Graham-Cumming's article on automatic detection of homophone sequences
  • John C. King & Dennis R. Bahler, "An Algorithmic Solution of Sequential Homophonic Ciphers". In their paper, King and Bahler describe an algorithm that can identify homophone sequences to simplify homophonic ciphers. Abstract
  • Brute force search for homophone sequences - Shows sequences detected in the 408 and 340 ciphers by performing brute force searches for sequences involving up to 6 symbols.

Images

Images from Michael Butterfield (zodiackillerfacts.com) and Tom Voigt (zodiackiller.com):

Part 1 - From Vallejo Times - Herald Letter - July 31 1969
Harden's worksheet for Part 1
Part 2 - From San Francisco Examiner Letter - July 31 1969
Harden's worksheet for Part 2
Clearer scan of Part 2
Part 3 - From San Francisco Chronicle Letter - July 31 1969
Harden's worksheet for Part 3
Clearer scan of Part 3

Other images:

High-resolution scan (unknown source)
traveller1st's recombination of the three sections

(traveller1st's post)

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