In WW2, later US president John F. Kennedy and his crew disappeared after their torpedo boat had sunk. Can my readers help to make sense of an encrypted message that was sent a few days later?

As many of my readers already know, I’m currently co-writing a book about codebreaking with my US friend Elonka Dunin. This work is already announced on Amazon, publication is scheduled for November.

One of the topics Elonka and I address in our book is the Playfair cipher. As an example, we plan to cover a Playfair message that has a close relationship to John F. Kennedy.

Kennedy took part in the Second World War as a young naval officer. In 1943, he commanded a military boat, PT-109 …

Source: Wikimedia Commons

…, which was crashed into by a Japanese destroyer. Kennedy and his crew washed up on the beach of a nearby island. Australian coastwatcher Sub-Lieutenant Reginald Evans, who had observed the crash, coordinated a successful rescue effort.

 

A Playfair message

During his coordination work, Evans sent and received multiple messages encrypted with the Playfair cipher. One of these messages is depicted in David Kahn’s book The Codebreakers.

Source: National Cryptologic Museum

The plaintext is noted below the message. It’s easy to read, and the ciphertext can be easily decrypted with the keyword ROYAL NEW ZEALAND NAVY.

The Playfair cipher used in this context follows the usual Playfair rules, except that doubled letters are not avoided by adding an X (e.g., OO becomes OXO before the substitution step), but are left unchanged (e.g, OO is encrypted to OO).

 

Another Playfair message

The National Cryptologic Museum has provided Elonka and me a few more ciphertexts of the same kind, also sent or received by Reginald Evans. As far as we know, these cryptograms have never been published in the crypto literature.

Here’s a Playfair message from August 7nd, 1943, five days after the crash:

Source: National Cryptologic Museum

Here’s a transcript of the ciphertext:

XELWA OHWUW YZMWI HOMNE OBTFW MSSPI AJLUO EAONG OOFCM FEXTT CWCFZ YIPTF EOBHM WEMOC SAWCZ SNYNW MGXEL HEZCU FNZYL NSBTB DANFK OPEWM SSHBK GCWFV EKMUE

The keyword used was PHYSICAL EXPERIMENTATION, which led to the following Playfair matrix:

PHYSI
CALEX
RMNTO
BDFGK
QUVWZ

Again, the plaintext is noted next to the Playfair message. It starts with: ELEVEN SURVIVORS PT BOAT …

However, this time the (alleged) plaintext is hard to read. Elonka and I tried to decipher the cryptogram (with CrypTool 2 and the Rumkin.com Cipher Tools) and to match the result with the purported plaintext, but only the first few letters made sense.

In addition, we wonder why there is a J in the ciphertext, although the Playfair cipher is usually based on a 25-letter alphabet without a J.

Can a reader tell us how this ciphertext can be decrypted and if it matches the plaintext noted on the same sheet?

Of course, we will include everybody who provides a helpful advice in our acknowledgement list, which is a part of the first book chapter.


Further reading: My steganographic gravestone tour (1): The grave of William and Elizebeth Friedman

Linkedin: https://www.linkedin.com/groups/13501820
Facebook: https://www.facebook.com/groups/763282653806483/

Subscribe to Blog via Email

Enter your email address to subscribe to this blog and receive notifications of new posts by email.

Kommentare (20)

  1. #1 Norbert
    Berlin
    27. Mai 2020

    I think the correct keyphrase is
    PHYSICAL EXAMINATION:

    PHYSI
    CALEX
    MNTOB
    DFGKQ
    RUVWZ

  2. #2 Magnus Ekhall
    Borensberg
    27. Mai 2020

    I think Norbert is correct. The clear text would be something like:
    ELEVEN SURVIVORS PT BOAT ON GROSSIS X HAVE SENT FOOD AND LETTER ADVISING SENIOR COME HERE WITHOUT DELAY X WARN AVIATION OF CANOES CROSSING FERGUSON RA

  3. #3 Thomas
    27. Mai 2020

    The keyword isn´t PHYSICAL EXPERIMENTATION, but PHYSICAL EXAMINATION: https://books.google.de/books?id=3S8rhOEmDIIC&pg=PT619

  4. #4 Klaus Schmeh
    27. Mai 2020

    Norbert, Magnus, Thomas: Thank you very much!!

  5. #5 Klaus Schmeh
    27. Mai 2020

    Apparently, the J is used like an I.

  6. #6 Magnus Ekhall
    Borensberg
    27. Mai 2020

    At first I thought that Q might be the excluded letter in the alphabet, but that was not correct. Instead just converting the J to I gives a better result.
    I do not know what “Gross Is” is. Is there an island called Gross involved in this perhaps?

  7. #7 Bill Briere
    Wyoming, USA
    27. Mai 2020

    Yes, PHYSICAL EXAMINATION. I got the same result by reconstructing a functional table from the “nongarbles,” leaving only R, B, and Q unconfirmed in my table. There ended up being a little bit more to it than that, but it was pretty obvious how to fix the garbled (incorrect) key from there.

  8. #8 Norbert
    Berlin
    27. Mai 2020

    Thomas is right, my printed edition of “The Codebreakers” also gives the right keyphrase, as well as the correct plaintext. Now this is interesting. Did Elonka and Klaus use an older edition which has the wrong key? Did they make a mistake while copying it? Or did Klaus modify the key on purpose, to give us a riddle? Klaus, you owe us an explanation 🙂

  9. #9 Bill Briere
    Wyoming, USA
    27. Mai 2020

    @Klaus What other messages do you have from the keen-eyed Australian coastwatcher Evans? And does the NCM have the original scraps of paper, or are they just copies?

  10. #10 Magnus Ekhall
    Borensberg
    27. Mai 2020

    I got the end of the message wrong. The ciphertext is actually of odd length. The final “E” is left in the clear. So the message ends with RE, the initials of the sender I guess:

    ELEVEN SURVIVORS PT BOAT ON GROSS IS X HAVE SENT FOOD AND LETTER ADVISING SENIOR COME HERE WITHOUT DELAY X WARN AVIATION OF CANOES CROSSING FERGUSON RE

  11. #11 Magnus Ekhall
    Borensberg
    27. Mai 2020

    The correct clear text should be “Cross Is”, not “Gross Is”.
    Cross Island was another name for Naru Island apparently.

  12. #12 Bob Bogart
    Glen Rock, PA, USA
    28. Mai 2020

    Interesting how the on-cut TT at positions 49 and 50 of the cipher gave plaintext TT. No null X was used to split the doublet, perhaps because X was used as a sentence separator?

  13. #13 Klaus Schmeh
    28. Mai 2020

    Corey Copeland via Facebook:
    Really looking forward to the new book!

  14. #14 Richard Bean
    Brisbane
    28. Mai 2020

    Bob B: yes, The Codebreakers p. 593 which gives the plain text and key also says “departing from traditional Playfair only by leaving doubled letters unenciphered, as the s’s in Gross and crossing”

  15. #15 Magnus Ekhall
    Borensberg
    28. Mai 2020

    @Bean: Is the plain text “Gross Is” according to The Codebreakers?
    I think that is an error made by Evans when enciphering the message in that case.

  16. #16 Norbert
    Berlin
    28. Mai 2020

    @Magnus: In “The Codebreakers” (1996 edition, p. 593), David Kahn writes “Gross” several times.

    Two natives had found the sailors, who had moved to Gross Island, and had reported the find to Evans. He wrote a brief message: Eleven survivors PT boat an Gross Is X (…)”

    Also the passage quoted by Richard Bean (#14) has Gross.

  17. #17 Max Baertl
    28. Mai 2020

    Maybe the „RE“ at the end stands for „Reginald Evans“

  18. #18 Klaus Schmeh
    28. Mai 2020

    >Klaus, you owe us an explanation
    Here it is. The key noted on the sheets we received from the museum is PHYSICAL EXPERIMENTATION.

    To my regret, I didn’t check Kahn’s book. Otherwise, I would have seen that this key is wrong. Sorry.

  19. #19 Klaus Schmeh
    28. Mai 2020

    Thanks to all for solving this mystery!
    Thomas, Norbert, Richard, Magnus and Bill are already mentioned in my book. I will add Max Bärtl and Bob Bogart to the acknowledgement list.

  20. #20 Thomas
    28. Mai 2020

    @Klaus
    Thank you very much for mentioning me in your book!

    I suppose that it wasn’t Evans who scribbled the wrong key on the sheet. What would have happend with J.F.K. otherwise?