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Exploring these mysterious transmissions and how their strong following has created a niche in the community.
Scanning through the bands on AM, you stumble upon something odd. It might be the last few notes of a folk song, a sound clip from an old cartoon, or phrases in a different language. A voice cuts through the static, methodically calling out, "Mike, India, Whiskey, One, Four..." But this isn't a fellow ham announcing their call sign. These are numbers stations, an eerie subset of radio stations that has intrigued hams and non-hams alike for decades.
Behind the Voices
Numbers stations are shortwave AM radio stations that transmit messages via voice or Morse code, believed to be coded in onetime pad (OTP) cryptography. In OTPs, the message is comprised of strings of numbers or letters assigned to the letters of the message, based on a pre-determined, randomized key shared between the transmitting and receiving parties. This is the simplest method of "perfect" encryption, which means mathematically, it is unbreakable.
There are some rules that define one-time pad encryption: the randomized characters must be the same length as the plain text of the message so none of it is reused, and only two copies of the OTP exist (one for the transmitter and one for the receiver), which are used once and then destroyed immediately. These keys were named after the pads of paper they were printed on, and the user could tear off the top sheet after use and dispose of it.
The randomization of the one-time pad for each new transmission leaves no pattern, so a listener would not be able to analyze multiple transmissions to figure out a key. In order to decrypt the message, this third party would not only have to get hold of the OTP, but also know which key was used in the transmission.
Famous Stations
Most numbers stations were first heard throughout the Cold War era, and some were so consistent or idiosyncratic that they become popular among those who monitored them. The Lincolnshire Poacher, first identified in the 1970s, became known by playing a few notes from the famous British folk song of the same name before each transmission. It is thought to have been run by the...