Number stations are spooky

Number stations are shortwave transmissions from foreign intelligence agencies to spies in the field of foreign countries. They carry encrypted messages in form of groups of numbers or letters, using either automated voice, Morse code, or a digital mode. While the encryption methods used by most number stations are unknown, some have used and others are widely believed to use one-time pad: mathematical addition of a set of random numbers (the key) to the cleartext, which can be used only once, and must be destroyed after usage.

As number stations are part of classified intelligence operations, very few government organizations have released information about them; those that have include the Polish Institute of National Remembrance and other Polish archives, the Swedish Security Service, and the National Archives of Latvia. Additionally, number stations have been involved in the publicly prosecuted espionage cases of Kim Hyon-hui (1987), Václav Jelínek (1988), the Cuban Five (1998), Ana Montes (2001), the Illegals Program (2010), and Andreas and Heidrun Anschlag (2011).

Number stations offer a powerful advantage in our modern world: practically complete anonymity. The recipient of the message can be almost anywhere in the world, and receive instructions without fear of being traced through a phone call or internet connection. All the recipient needs is a shortwave radio and to be in the right place at the right time.