The effect of scintillation on radio signals whose propagation path involves the Earth’s ionosphere is analogous to the allies of World War II receiving radio messages that had passed through the Enigma machine. In both these cases, man-made information has been encrypted and transmitted via radio. The two encryption methods are shown in Figure 1. The right panel shows a World War II Enigma machine used extensively by German U-boats to convey encrypted messages transmitted by radio [Perera, 2010]. The left panel gives an extreme example of a mapping of ionospheric irregularities at 3 m, which creates very severe scintillation on radio communications through this ionospheric region [Fejer, 1996]. In addition, the task of formally deciphering the encrypted signal is a monumental task as time is of the essence and old information quickly becomes redundant.
Sojka, J. J. (2013). Ionospheric Induced Scintillation: A Space Weather Enigma: FEATURE. Space Weather, 11(4), 134–137. doi:10.1002/swe.20041