2 The Caesar cipher
Figure 2-1: The message on this 1939 telegram is encrypted with a Caesar cipher.
The telegram depicted in Figure 2-1 (and provided to us by Karsten Hansky) was sent from St Leonards-on-Sea, United Kingdom, to Georgetown, British Guyana, in 1939.1 The message on this telegram is partially encrypted. In the following transcript, the ciphertext is printed in bold on the fourth line:
CDE.
BRG9.IDCH. STLEONARDSONSEA. 10. 9th. 13.20.
ROBERTSON TREASURY GEORGETOWNBG.
JKHQY GYULN QOOWE HAWNH EAOPL KODEX HAHQR.
10.25AM.
The encryption ...
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