In the shadowy corners of the shortwave spectrum lurk the Numbers Stations: strange radio broadcasts of mysterious blocks of numbers in creepy monotone voices!
It's actually an old form of spycraft which is still in use today. And as it's #WorldRadioDay let's take a listen...
A Numbers Station is a type of one-way voice link for sending information to spies in foreign countries.
Operating on Short Wave radio bands they transmit a secret code of spoken numbers. Use of Numbers Stations peaked during the Cold War, but some are still operating today.
Numbers Stations are operated by various national intelligence agencies. At set times on a pre-arranged frequency a musical tone is played, followed by a speech synthesised voice reading out blocks of numbers. To most listeners it sounds both creepy and meaningless.
However to spies it can be vital. The numbers can be decoded to reveal a message, provided the spy has the right One Time Pad (OTP) - a random number key that is only used once before it is destroyed. OTP encryption is impossible to break if done correctly.
Why broadcast your secret message on Short Wave? Because it can be picked up across the globe. All a spy needs is a shop bought SW radio, a pencil, and the correct One Time Pad and they - and only they - can decipher the message. No complex kit is required.