The Importance of Breaking the Enigma Code
Enigma machines, developed originally in Germany in the 1920s, were the first electromechanical encryption devices and would eventually carry Nazi Germany's military communications during World War II. The cracking of that code at Bletchley Park would play a key role in shortening the war and saving countless lives.
The Enigma Machine
Dr Arthur Scherbius had developed his 'Enigma' machine, capable of transcribing coded information, in the hope of interesting commercial companies in secure communications. By 1926 the German navy was producing its own version, followed in 1928 by the army and in 1933 by the air force.
Enigma allowed an operator to type in a message, and then scrambles it by means of three to five notched wheels, or rotors, which displayed different letters of the alphabet. The receiver needed to know the exact settings of these rotors in order to reconstitute the coded text. Over the years the basic machine became more complicated, as German code experts added plugs with electronic circuits.
The Polish government was the first to make significant progress in breaking the Enigma code.
In January 1929 Polish customs intercepted a packaged sent from Germany to a German company in Warsaw. The packaged contained an unknown crypto machine (early version of ENIGMA). After Polish Intelligence took photographs and made drawings to be used in the future the machine was repackaged and sent back to the Germans in order not to raise suspicion that the package had been intercepted. Later that same year French Intelligence discovered from an independent source that the Germans had been working on a new encrypting machine called Enigma since 1926.
In the fall of 1931 a German cryptologist approached French intelligence with an offer to sell infrormation relating to military intelligence and cryptology and was provided with details on how to construct the prototype machine. The French aware of the Polish attempts in breaking German codes shared this information with the Polish cryptographers and the Polish using this information were able to reconstruct the wiring of the Enigma rotors.
This allowed the Polish cryptology team to sort German coded messages into quarterly and daily groupings for analysis.
Shortly before Poland was invaded by Germany the Polish turned over the progress they had made in decrypting the Enigma code to British Intelligence who continued to work on the decryption of the German codes.
The Enigma Machine
- Rotors at top left could be rotated to different settings, to generate different codes - more rotors made the code more difficult to crack
- The message was typed into the machine using typewriter keys at the front
- Each time a letter was typed a lamp lit up one of the letters in the middle of the machine - this illuminated letter then formed part of the cipher text
- Later models, such as the German military machine on the right, had a plugboard at the front (under the operator's hand), which added an additional level of complexity
Dr Arthur Scherbius had developed his 'Enigma' machine, capable of transcribing coded information, in the hope of interesting commercial companies in secure communications. By 1926 the German navy was producing its own version, followed in 1928 by the army and in 1933 by the air force.
Enigma allowed an operator to type in a message, and then scrambles it by means of three to five notched wheels, or rotors, which displayed different letters of the alphabet. The receiver needed to know the exact settings of these rotors in order to reconstitute the coded text. Over the years the basic machine became more complicated, as German code experts added plugs with electronic circuits.
The Polish government was the first to make significant progress in breaking the Enigma code.
In January 1929 Polish customs intercepted a packaged sent from Germany to a German company in Warsaw. The packaged contained an unknown crypto machine (early version of ENIGMA). After Polish Intelligence took photographs and made drawings to be used in the future the machine was repackaged and sent back to the Germans in order not to raise suspicion that the package had been intercepted. Later that same year French Intelligence discovered from an independent source that the Germans had been working on a new encrypting machine called Enigma since 1926.
In the fall of 1931 a German cryptologist approached French intelligence with an offer to sell infrormation relating to military intelligence and cryptology and was provided with details on how to construct the prototype machine. The French aware of the Polish attempts in breaking German codes shared this information with the Polish cryptographers and the Polish using this information were able to reconstruct the wiring of the Enigma rotors.
This allowed the Polish cryptology team to sort German coded messages into quarterly and daily groupings for analysis.
Shortly before Poland was invaded by Germany the Polish turned over the progress they had made in decrypting the Enigma code to British Intelligence who continued to work on the decryption of the German codes.
A host of top mathematicians and general problem-solvers was recruited, and a bank of early computers, known as 'bombes', was built - to work out the vast number of permutations in Enigma settings.
The Germans were convinced that Enigma output could not be broken, so they used the machine for all sorts of communications - on the battlefield, at sea, in the sky and, significantly, within its secret services. The British described any intelligence gained from Enigma as 'Ultra', and considered it top secret.
Thanks to the information from the Poles, the British had learned to read parts of the German Armed Forces signals traffic, regular decrypts only became possible in the Norwegian campaign - and then they were of marginal operational use.
In 1941 Enigma decrypts begin to pay dividends. In the spring they provided evidence of a German military build-up prior to the invasion of Greece, although the Allies did not have a large enough military force to exploit this breakthrough.
In March, Bletchley's reading of the Italian navy's Enigma material helped Admiral Cunningham's Mediterranean fleet defeat the Italians at the Battle of Matapan. And in the autumn, the cryptanalysts broke ciphers used by Marshal Rommel's Panzer army, both within its own units and in communications with Rome and Berlin, giving the Allies an important advantage in North Africa.
The greatest threat to the Allied war effort came from attacks on their ship convoys in the North Atlantic. As a result, Bletchley's resources were concentrated on breaking Enigma codes used by German U-boats. If the Allies could find out in advance where U-boats were hunting, they could direct their ships, carrying crucial supplies from North America, away from these danger zones.
So began one of the most exciting periods of Enigma code-breaking.
It soon became clear that the best way of keeping up with rapid changes in ciphers and related technology was to capture Enigma machines and code-books on board German vessels.
The German trawler Krebs was captured in March 1941, off the cost of Norway, complete with two Enigma machines and the Naval Enigma settings list for the previous month. This allowed German Naval Enigma to be read, albeit with some delay, in April, by code breakers at Bletchley.
In February 1942 the Germans hit back by introducing a new fourth wheel (multiplying the number of settings another 26 times) into their Naval Enigma machines. The resulting 'net' was known to the Germans as 'Triton' and to the British as 'Shark'. For almost a year Bletchley could make no inroads into Shark, and Allied losses in the Atlantic again increased alarmingly.
In December 1942 Shark was broken, but German innovations meant that the Allies had to wait until August the following year before Naval Enigma was regularly read again. By then the Americans were active combatants, providing much-needed computer power to Bletchley.
How much did Ultra intelligence, gained from reading Enigma ciphers, shorten the war? Harry Hinsley, based at Bletchley during the war, suggests it was a significant asset. If it did not keep Rommel out of Egypt in 1941, it certainly did so the following year, by preventing him exploiting his victory at Gazala.
As General Alexander put it, 'The knowledge not only of the enemy's precise strength and disposition, but also how, when and where he intends to carry out his operations brought a new dimension to the prosecution of the war.'
The loss of Egypt in 1942 would have set back the re-conquest of North Africa and upset the timetable for the invasion of France. According to Hinsley, Operation Overlord would probably have been deferred until 1946.
Enigma successes always needed to be complemented with other intelligence material to mask the fact that the Allies could decipher military messages.
The Germans were convinced that Enigma output could not be broken, so they used the machine for all sorts of communications - on the battlefield, at sea, in the sky and, significantly, within its secret services. The British described any intelligence gained from Enigma as 'Ultra', and considered it top secret.
Thanks to the information from the Poles, the British had learned to read parts of the German Armed Forces signals traffic, regular decrypts only became possible in the Norwegian campaign - and then they were of marginal operational use.
In 1941 Enigma decrypts begin to pay dividends. In the spring they provided evidence of a German military build-up prior to the invasion of Greece, although the Allies did not have a large enough military force to exploit this breakthrough.
In March, Bletchley's reading of the Italian navy's Enigma material helped Admiral Cunningham's Mediterranean fleet defeat the Italians at the Battle of Matapan. And in the autumn, the cryptanalysts broke ciphers used by Marshal Rommel's Panzer army, both within its own units and in communications with Rome and Berlin, giving the Allies an important advantage in North Africa.
The greatest threat to the Allied war effort came from attacks on their ship convoys in the North Atlantic. As a result, Bletchley's resources were concentrated on breaking Enigma codes used by German U-boats. If the Allies could find out in advance where U-boats were hunting, they could direct their ships, carrying crucial supplies from North America, away from these danger zones.
So began one of the most exciting periods of Enigma code-breaking.
It soon became clear that the best way of keeping up with rapid changes in ciphers and related technology was to capture Enigma machines and code-books on board German vessels.
The German trawler Krebs was captured in March 1941, off the cost of Norway, complete with two Enigma machines and the Naval Enigma settings list for the previous month. This allowed German Naval Enigma to be read, albeit with some delay, in April, by code breakers at Bletchley.
In February 1942 the Germans hit back by introducing a new fourth wheel (multiplying the number of settings another 26 times) into their Naval Enigma machines. The resulting 'net' was known to the Germans as 'Triton' and to the British as 'Shark'. For almost a year Bletchley could make no inroads into Shark, and Allied losses in the Atlantic again increased alarmingly.
In December 1942 Shark was broken, but German innovations meant that the Allies had to wait until August the following year before Naval Enigma was regularly read again. By then the Americans were active combatants, providing much-needed computer power to Bletchley.
How much did Ultra intelligence, gained from reading Enigma ciphers, shorten the war? Harry Hinsley, based at Bletchley during the war, suggests it was a significant asset. If it did not keep Rommel out of Egypt in 1941, it certainly did so the following year, by preventing him exploiting his victory at Gazala.
As General Alexander put it, 'The knowledge not only of the enemy's precise strength and disposition, but also how, when and where he intends to carry out his operations brought a new dimension to the prosecution of the war.'
The loss of Egypt in 1942 would have set back the re-conquest of North Africa and upset the timetable for the invasion of France. According to Hinsley, Operation Overlord would probably have been deferred until 1946.
Enigma successes always needed to be complemented with other intelligence material to mask the fact that the Allies could decipher military messages.