In the intelligence world, one of the key disciplines is communicating information securely. If this sounds familiar, that’s because it is, albeit for different reasons. Since the invention of radio communication – or “wireless telegraphy,” if you prefer – has been the Numbers Station.
To understand what a numbers station (One-Way Voice Link, or OWVL), is the technical term) is, we briefly have to discuss cryptography.
In its simplest form, cryptography is the art of making and breaking codes. Over the course of human history, many states and leaders have come up with various, often ingenious, codes and ciphers, as well as the means to both break them and manipulate them. Sir Francis Walsingham, official spymaster for the first Queen Elizabeth, was responsible (among many other things) for the interception and breaking of the ciphers used by Mary, Queen of Scots – an intelligence operation that resulted in that monarch’s execution. Likewise, the “polyalphabetic substitution cipher”, invented by an Italian cryptographer named Giovan Battista Bellaso in 1553 (better known as the Vigenère cipher), was so strong, it remained unbroken until 1863. There are many other systems – ancient, new and unique – but all share the same fundamental flaw: Key Distribution.
In cryptography, encipherment and decipherment are relatively easy, but only if both sender and receiver share the code – and written codes, as proved by Walsingham – can be intercepted, opening messages’ secrets that could and did lead to war, death and betrayal.
Heavy stuff.
The goal of key distribution was only solved – for a time, at least – by the invention of PGP (Pretty Good Privacy) in the 1990’s…but that’s for another time.
But the problem, ‘back in the day’, seemed insurmountable: in order to decipher a message, the receiver required a copy of the code, a serious problem if a considerable distance separated sender and receiver. The Vigenère cipher, however, significantly reduced that problem through what we would now call “keywords”. Still, as was proven in 1854 by English mathematician and scientist Charles Babbage, Prussian army Major Friedrich Wilhelm Kasiski in 1863, and by American engineer William F. Friedman in the 1920’s, the Vigenère cipher model could, and was, breakable, via frequency analysis.
As early as World War 1, strange radio transmissions in the short-wave band began to be heard over the public airwaves. These stations transmitted signals in Morse Code, but the transmissions were not encoded. Instead, they were just strings of letters, numbers, and occasionally both. It quickly became apparent that these signals were almost certainly in a code of some kind, but no one – in public, at least – was able to decode the signals. They were resistant to frequency attacks, and seemed to be immune to proven forms of cryptanalytic attack.
This was the births of the One-Time Pad (OTP) and the Numbers Station.
First outlined in 1882 by the American banker Frank Miller, the OTP was reinvented in 1917, patented in the United States by Gilbert Vernam and Joseph Mauborgne (pdf link). In this coding system, random strings of letters or numbers (and sometimes both) were added or subtracted against a list of random numbers, to produce an enciphered message. The receiver – who would have a copy of the list of numbers – would, using their copy of the list – work in reverse, to reveal the message. Once received and decrypted, both sender and receiver would cross out the section of the numbers list they had used…and never use those exact sequences again.
And, up to this day, as long as the strict requirements of the system are followed, the messages are indecipherable, unless a decrypter has access to the key. (For a full discussion of the practical use of OTP’s, visit this PDF file).
What someone had realized was that an encoded signal did not have to go via telephone, telegraph or mail, all of which were open to interception. Instead, all a secret agent in the field needed, was a radio capable of picking up the Morse signals on the proper frequency, to receive a message. And, with the OTP, the agent’s “codebook” was shrunken to the size of a roll of postage stamps.
As time went on, wireless radio moved from Morse to verbal speech, helping to eliminate errors in transmission. National intelligence services constructed powerful shortwave transmission towers in areas they controlled around the world, and – in addition to the normal propaganda broadcasts and music they would play – would periodically pause, and transmit strings of letters and/or numbers at specific times of the day.
Counterintelligence officers found this highly frustrating, because there was no way to monitor who had a simple radio receiver. Capturing agents was usually through those agent’s mistakes, not through any kind of cunning technology.
And that is where things stand, to this day. Numbers stations transmit messages “in the clear,” and unless someone makes a mistake, there is no way to decipher the messages. No nation, incidentally, will openly admit to operating a numbers station, and will only rarely acknowledge their existence, as happened in the “Atención spy case”, where the bumbling of a group of agents from Fidel Castro’s Cuba rolled up a network of some twenty-seven agents, among many other operations.
There are civilian monitoring groups out on the internet for the interested sleuth, such as the Numbers Stations Research & Information Center, and PRIYOM.
…Just…please don’t get caught doing dumb things. If certain parties in government think you are up to no good, you won’t be able to catch our articles on time.
Priorities, you know.
