Secret broadcast
Encyclopedia
A secret broadcast is, simply put, a broadcast that is not for the consumption of the general public. The invention of the wireless
was initially greeted as a boon by armies and navies. Units could now be coordinated by nearly instant communications. It soon became clear that radio was a double edged sword. An adversary could glean valuable and sometimes decisive intelligence from intercepted radio signals:
In the 1920s the United States
was able to track Japan
ese fleet exercises even through fog banks by monitoring their radio transmissions.
A doctrine was developed of having units in the field, particularly ships at sea, maintain radio silence except for urgent situations, such as reporting contact with enemy forces. Ships in formation reverted to pre-wireless methods, including semaphore
and signal flags, with signal lamps used at night. Communication from headquarters were sent by one-way radio broadcasts.
stations. Later radioteletype
was used. Sensitive messages were encrypted. Call signs were encrypted as well to provide traffic-flow security. Some messages (weather forecasts, intelligence reports) were sent to the fleet as a whole. Operators on-board ship would monitor the fleet broadcast, decoding messages intended for their ships. Messages might be repeated several times on different frequencies to ensure reception, but were generally not acknowledged. During and after World War II
rotor machine
encryptors, such as SIGABA
and KL-7
were used to decode messages off-line. In the 1960s in-line radioteletype decoders, such as the KW-37
, were introduced. These were replaced in the 1980s by the Fleet Satellite Communications System and the KW-46 encryption system, which supported speeds up to 9600 bit/s. These in turn have been replaced with units offering the even higher speeds needed for "network centric" warfare and the dissemination of high bandwidth intelligence information, such as satellite imagery.
would include "personal messages" in its broadcasts of news and entertainment to occupied-Europe. Often they were coded messages intended for secret agents. Leo Marks
attributes this idea to Georges Bégué
, an agent for the Special Operations Executive
who felt their use could eliminate a lot of the two-way radio traffic that often compromised agents. Such messages were also used to authenticate agents to sources of assistance in the field. The agent would arrange to have the BBC broadcast any short phrase the other person chose.
radio bands were used by numerous stations sending seemingly random Morse code, usually in five-letter groups. As more advanced communications methods, such as teleprinter
and satellite, took over, the number of such stations diminished, but another type appeared that transmitted spoken and also seemingly random number and letter groups, the latter usually using words from a radio alphabet such as ICAO/NATO alphabet
.
Though there has been no official confirmation (beyond a 1998 article in The Daily Telegraph which quoted a spokesperson for the Department of Trade and Industry as saying, "These [numbers stations] are what you suppose they are. People shouldn't be mystified by them. They are not for, shall we say, public consumption.") there is little doubt that most of these numbers stations are primarily used to send messages to spies
and other clandestine agents (additional possible uses include communication with embassies when a crisis might dictate destruction of cryptographic equipment and as a backup to normal command systems in wartime). Other intended recipients of secret broadcasts have faster and easier-to-use equipment at their disposal. But number stations are ideal for spies in that they require no special equipment, beyond a short-wave receiver. Morse code skills, once a staple of spy training, are no longer required.
where an order removing the Liberty from proximity to hostile fire was not transmitted via the proper fleet broadcast station until after the ship came under attack. Another issue in the past has been the limited bandwidth of the broadcast. Morse code was typically sent at 25 words per minute. Teletype could operate at 60 words per minute. The military uses a message precedence
system to prioritize critical traffic, but all too often, senior commanders insisted on high precedence for lengthy messages lacking real urgency.
Wireless
Wireless telecommunications is the transfer of information between two or more points that are not physically connected. Distances can be short, such as a few meters for television remote control, or as far as thousands or even millions of kilometers for deep-space radio communications...
was initially greeted as a boon by armies and navies. Units could now be coordinated by nearly instant communications. It soon became clear that radio was a double edged sword. An adversary could glean valuable and sometimes decisive intelligence from intercepted radio signals:
- messages that were not encryptedEncryptionIn cryptography, encryption is the process of transforming information using an algorithm to make it unreadable to anyone except those possessing special knowledge, usually referred to as a key. The result of the process is encrypted information...
or poorly encrypted could be read - order of battleOrder of battleIn modern use, the order of battle is the identification, command structure, strength, and disposition of personnel, equipment, and units of an armed force participating in field operations. Various abbreviations are in use, including OOB, O/B, or OB, while ORBAT remains the most common in the...
and future intentions could be deduced by traffic analysisTraffic analysisTraffic analysis is the process of intercepting and examining messages in order to deduce information from patterns in communication. It can be performed even when the messages are encrypted and cannot be decrypted. In general, the greater the number of messages observed, or even intercepted and... - individual units could be located using direction findingDirection findingDirection finding refers to the establishment of the direction from which a received signal was transmitted. This can refer to radio or other forms of wireless communication...
In the 1920s the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
was able to track Japan
Japan
Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...
ese fleet exercises even through fog banks by monitoring their radio transmissions.
A doctrine was developed of having units in the field, particularly ships at sea, maintain radio silence except for urgent situations, such as reporting contact with enemy forces. Ships in formation reverted to pre-wireless methods, including semaphore
Flag semaphore
Semaphore Flags is the system for conveying information at a distance by means of visual signals with hand-held flags, rods, disks, paddles, or occasionally bare or gloved hands. Information is encoded by the position of the flags; it is read when the flag is in a fixed position...
and signal flags, with signal lamps used at night. Communication from headquarters were sent by one-way radio broadcasts.
U.S. Fleet Broadcast
For example, the U.S. Navy developed a series of transmitting sites throughout the world that sent a fleet broadcast to its vessels at sea. Initially these were Morse codeMorse code
Morse code is a method of transmitting textual information as a series of on-off tones, lights, or clicks that can be directly understood by a skilled listener or observer without special equipment...
stations. Later radioteletype
Radioteletype
Radioteletype is a telecommunications system consisting originally of two or more electromechanical teleprinters in different locations, later superseded by personal computers running software to emulate teleprinters, connected by radio rather than a wired link.The term radioteletype is used to...
was used. Sensitive messages were encrypted. Call signs were encrypted as well to provide traffic-flow security. Some messages (weather forecasts, intelligence reports) were sent to the fleet as a whole. Operators on-board ship would monitor the fleet broadcast, decoding messages intended for their ships. Messages might be repeated several times on different frequencies to ensure reception, but were generally not acknowledged. During and after World War II
World War II
World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...
rotor machine
Rotor machine
In cryptography, a rotor machine is an electro-mechanical device used for encrypting and decrypting secret messages. Rotor machines were the cryptographic state-of-the-art for a prominent period of history; they were in widespread use in the 1920s–1970s...
encryptors, such as SIGABA
SIGABA
In the history of cryptography, the ECM Mark II was a cipher machine used by the United States for message encryption from World War II until the 1950s...
and KL-7
KL-7
The TSEC/KL-7, code named ADONIS and POLLUX, was an off-line non-reciprocal rotor encryption machine. The KL-7 had eight rotors to encrypt the text, seven of which moved in a complex pattern, controlled by notched rings. The non-moving rotor was in fourth from the left of the stack. The encrypted...
were used to decode messages off-line. In the 1960s in-line radioteletype decoders, such as the KW-37
KW-37
The KW-37, code named JASON, was an encryption system developed In the 1950s by the U.S. National Security Agency to protect fleet broadcasts of the U.S. Navy. Naval doctrine calls for warships at sea to maintain radio silence to the maximum extent possible to prevent ships from being located by...
, were introduced. These were replaced in the 1980s by the Fleet Satellite Communications System and the KW-46 encryption system, which supported speeds up to 9600 bit/s. These in turn have been replaced with units offering the even higher speeds needed for "network centric" warfare and the dissemination of high bandwidth intelligence information, such as satellite imagery.
"Personal messages" on propaganda stations
During WWII, the BBCBBC
The British Broadcasting Corporation is a British public service broadcaster. Its headquarters is at Broadcasting House in the City of Westminster, London. It is the largest broadcaster in the world, with about 23,000 staff...
would include "personal messages" in its broadcasts of news and entertainment to occupied-Europe. Often they were coded messages intended for secret agents. Leo Marks
Leo Marks
Leopold Samuel Marks was an English cryptographer, screenwriter and playwright.-Early life:Born the son of an antiquarian bookseller in London, he was first introduced to cryptography when his father showed him a copy of Edgar Allan Poe's story, "The Gold-Bug"...
attributes this idea to Georges Bégué
Georges Bégué
Georges Bégué or George P. Begue was a French engineer and agent in the Special Operations Executive.-Early life:...
, an agent for the Special Operations Executive
Special Operations Executive
The Special Operations Executive was a World War II organisation of the United Kingdom. It was officially formed by Prime Minister Winston Churchill and Minister of Economic Warfare Hugh Dalton on 22 July 1940, to conduct guerrilla warfare against the Axis powers and to instruct and aid local...
who felt their use could eliminate a lot of the two-way radio traffic that often compromised agents. Such messages were also used to authenticate agents to sources of assistance in the field. The agent would arrange to have the BBC broadcast any short phrase the other person chose.
Numbers stations
In the mid-twentieth century, the High FrequencyHigh frequency
High frequency radio frequencies are between 3 and 30 MHz. Also known as the decameter band or decameter wave as the wavelengths range from one to ten decameters . Frequencies immediately below HF are denoted Medium-frequency , and the next higher frequencies are known as Very high frequency...
radio bands were used by numerous stations sending seemingly random Morse code, usually in five-letter groups. As more advanced communications methods, such as teleprinter
Teleprinter
A teleprinter is a electromechanical typewriter that can be used to communicate typed messages from point to point and point to multipoint over a variety of communication channels that range from a simple electrical connection, such as a pair of wires, to the use of radio and microwave as the...
and satellite, took over, the number of such stations diminished, but another type appeared that transmitted spoken and also seemingly random number and letter groups, the latter usually using words from a radio alphabet such as ICAO/NATO alphabet
NATO phonetic alphabet
The NATO phonetic alphabet, more accurately known as the NATO spelling alphabet and also called the ICAO phonetic or spelling alphabet, the ITU phonetic alphabet, and the international radiotelephony spelling alphabet, is the most widely used spelling alphabet...
.
Though there has been no official confirmation (beyond a 1998 article in The Daily Telegraph which quoted a spokesperson for the Department of Trade and Industry as saying, "These [numbers stations] are what you suppose they are. People shouldn't be mystified by them. They are not for, shall we say, public consumption.") there is little doubt that most of these numbers stations are primarily used to send messages to spies
Spies
Spies most commonly refers to people who engage in spying, espionage or clandestine operations.Spies may also refer to:- Media and entertainment :* Spies , a jazz fusion band* "Spies" , a song...
and other clandestine agents (additional possible uses include communication with embassies when a crisis might dictate destruction of cryptographic equipment and as a backup to normal command systems in wartime). Other intended recipients of secret broadcasts have faster and easier-to-use equipment at their disposal. But number stations are ideal for spies in that they require no special equipment, beyond a short-wave receiver. Morse code skills, once a staple of spy training, are no longer required.
Problems with secret broadcast
Messages sent via secret broadcast are not acknowledged. One example where this caused disaster was the USS Liberty incidentUSS Liberty incident
The USS Liberty incident was an attack on a United States Navy technical research ship, , by Israeli Air Force jet fighter aircraft and Israeli Navy torpedo boats, on June 8, 1967, during the Six-Day War. The combined air and sea attack killed 34 crew members , wounded 170 crew members, and...
where an order removing the Liberty from proximity to hostile fire was not transmitted via the proper fleet broadcast station until after the ship came under attack. Another issue in the past has been the limited bandwidth of the broadcast. Morse code was typically sent at 25 words per minute. Teletype could operate at 60 words per minute. The military uses a message precedence
Message precedence
-CCEB military precedence:The Combined Communications-Electronics Board , a five-nation joint military communications-electronics organization , uses the following message precedence designators, in descending order of importance:-FLASH :This precedence is reserved for initial enemy contact...
system to prioritize critical traffic, but all too often, senior commanders insisted on high precedence for lengthy messages lacking real urgency.
Sources
- David Kahn, The CodebreakersThe CodebreakersThe Codebreakers – The Story of Secret Writing is a book by David Kahn, published in 1967 comprehensively chronicling the history of cryptography from ancient Egypt to the time of its writing...
- Leo MarksLeo MarksLeopold Samuel Marks was an English cryptographer, screenwriter and playwright.-Early life:Born the son of an antiquarian bookseller in London, he was first introduced to cryptography when his father showed him a copy of Edgar Allan Poe's story, "The Gold-Bug"...
, Between Silk and Cyanide - U.S.Cryptologic History Report, Attack on a SIGINT Collector, the U.S.S. Liberty, U.S. National Security Agency, 1981 http://www.nsa.gov/liberty/liber00010.pdf
See also
- Letter beaconLetter beaconLetter beacons are radio transmissions of uncertain origin and unknown purpose, consisting of only a single repeating Morse code letter. They have been classified into a number of groups according to transmission code and frequency, and it is supposed that the source for most of them is Russia.They...
- Numbers stationNumbers stationA numbers station is a shortwave radio station of uncertain origin. In the 1950s, Time magazine reported that the numbers stations first appeared shortly after World War II and were using a format that had been used to send weather data during that war.Numbers stations generally broadcast...
- Pirate radio - Piracy in amateur and two-way radio
- Traffic flow security