In 1916, the USA bought the West Indian islands from Denmark. An encrypted telegram about this purchase, sent by the Danish ambassador, is available on a website.

Blog reader Christof Rieber from Vienna has made me aware of an article published on a blog about the history of the Danish-West Indies. The Danish West-Indies were a Danish colony in the Caribbean, consisting of a few islands.

 

Two telegrams

In 1917, Denmark sold the islands for 25 million dollars to the United States, who renamed them to United States Virgin Islands. The aforementioned blog post introduces two telegrams that were sent in 1916, during the negotiations between the USA and Denmark about the sales. The first telegram was sent by news agency Reuters from the Danish West-Indies to Copenhagen. The press had got wind of the planned sale and the negotiations could no longer be kept secret.

Source: Danish National Archives

The second telegram was sent on November 26th, 1916 by the Danish ambassador in Washington to the Ministry of Foreign Affairs in Copenhagen. This one is more interesting for us because it is encrypted:

Source: Danish National Archives

 

How was it encrypted?

According to the article, this telegram concerned which documents from the sales negotiations could be published. Neither the plaintext nor the encryption method used is mentioned in the post.

It is pretty likely that a code was used for encrypting this telegram. A (cryptographic) code is based on a codebook that lists a code group (in this case a five-digit number) for every commom word of a certain language.

Telegrams encrypted in a code are nothing unusual. Governments, military organisations, and diplomatic services usually had their own codebooks, which were, of course, kept secret. Can a user identify the codebook or decrypt the telegram in a different way?

The two best sources for historical codebooks are the websites of Satoshi Tomokiyo and John McVey. Of course, checking the material the author of the aforementioned blog article found in the Danish National Archives is another option to solve this mystery.

Edited to add: In the original version of this article I wrote that the encrypted telegram was written from the Danish government to the US government. I corrected this.


Further reading: An unsolved encrypted telegram from the early 20th century

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 (6)

  1. #1 Dampier
    16. November 2019

    These sentences are a contradiction to me:

    it was sent from one government to another. So, neither a US codebook nor a Danish codebook could be used.

    by the Danish ambassador in Washington to the Ministry of Foreign Affairs in Copenhagen

    They could have used a danish codebook then. Did I get something wrong?

    a code group (in this case a five-digit number)

    Someone seems to have separated the numbers into groups of four, using a pen.

  2. #2 Thomas
    16. November 2019

    Pretty sure the code groups consist of four digits, as Dampier pointed out (see the repeating groups, esp. 0313, 1833). The five digit groups are due to telegraphic usage, usually the text was devided in groups of five. As for ‘722’: Either the telegram had a second page or 722 was just used to fill the last group. The frequencies:

    0313 4
    0316 1
    0319 1
    0351 1
    0395 1
    0602 1
    0686 1
    1211 1
    1273 1
    1587 1
    1833 9
    1851 1
    2500 1
    2773 1
    3011 3
    3040 2
    3092 1
    3340 1
    3637 1
    3642 2
    3921 1
    3940 1
    4078 1
    4120 1
    4168 1
    4204 2
    4259 2
    4450 1
    4778 1
    4820 1
    4915 1
    4976 2
    5035 1
    5216 1
    5427 1
    5434 1
    5887 1
    6116 1
    6127 1
    6193 1
    6304 1
    6543 1
    6707 1
    7035 1
    7215 1
    7500 1
    7645 1
    7680 1
    7845 1
    7893 1
    7988 1
    8011 1
    8091 2
    8196 1
    8323 1
    8561 1
    8952 1
    9080 2

  3. #3 Thomas
    16. November 2019

    @Dampier

    Agreed, since the Danish ambassador wrote to the Danish foreign ministry, most likely a Danish codebook with Danish plaintext entries was used (any Danish codebook experts out there?). The article states that the encrypted telegram concerns which documents from the secret sales negotiations between the Danish and American governments could be published. Hence the plaintext seems to be known (and maybe kept by the Danish National Archives).

  4. #4 Jarl
    Belgium
    16. November 2019

    To me it looks like a polyalphabetic where every single digit could be n letters:

    44507 64515 87121 10316 89523 92149 15801 18091 42591
    83375 00721 57680 61270 35142 04477 88196 78933 34003
    13183 34120 18515 42730 40497 68561 61932 50058 87908
    00395 18334 82030 11060 26543 50351 83378 45301 10313
    41681 83370 35301 14204 63043 04052 16611 60686 40784
    97680 91425 91833 30926 70754 34183 31273 39400 31379
    88183 32773 36420 31390 80031 91833 36373 64283 23772

  5. #5 Klaus Schmeh
    16. November 2019

    @Dampier, Thomas: You’re right, it must be a Danish codebook (if a codebook was used at all). I corrected it.

  6. #6 Richard SantaColoma
    http://proto57.wordpress.com/
    16. November 2019

    I agree that this probably consists of four number groups, not five. If so, then the black pen dividing lines are the decoder’s, and several words or names might be in that same pen:

    6543 are “mj”, and 3011 is “murry” or “murry”, 3642 is “Any”, or “Arty”, or like…

    … and then, if that is correct, it would be a code book, because the number of letters does not match 4, in all cases.

    I tried to find any “Murry” associated with “Transfer Day”, or the sale itself, or diplomacy at the time, but could only find one case in use, in a fiction.

    https://en.wikipedia.org/wiki/Transfer_Day