John Herivel
Encyclopedia
John W. Herivel was a British science historian and former World War II
codebreaker
at Bletchley Park
.
As a codebreaker concerned with Cryptanalysis of the Enigma
, Herivel is remembered chiefly for the discovery of what was soon dubbed the Herivel tip or Herivelismus. The "tip" was an insight into the habits of German operators of the Enigma cipher machine
that allowed Bletchley Park to easily deduce part of the daily key
. For a brief but critical few months from May 1940, the Herivel tip in conjunction with "cillies" (another class of operator error) was the main technique used to solve Enigma.
Herivel wrote books and articles on Isaac Newton
, Joseph Fourier
, Christiaan Huygens, and an autobiographical account of his work at Bletchley Park, Herivelismus.
, and attended Methodist College Belfast
from 1924 to 1936. In 1937 he was awarded a Kitchener Scholarship to study mathematics at Sidney Sussex College, Cambridge
. Shortly thereafter, Herivel was recruited to Bletchley Park by his former supervisor Gordon Welchman
, head of the newly formed Hut 6
section created to solve Army and Air Force Enigma. Herivel, then aged 21, arrived at Bletchley on 29 January 1940, and was briefed on Enigma by Alan Turing
and Tony Kendrick.
At the time, Hut 6 were having only limited success with the Luftwaffe
Enigma network known as "Red". Herivel was working alongside David Rees
, another Cambridge mathematician recruited by Welchman, in nearby Elmers School, testing candidate solutions and working out plugboard settings. The process was slow, however, and Herivel was determined to find a method to improve their attack, and would spend his evenings trying to think up ways to do so. One evening in the middle of February 1940 he was considering the procedures followed by a German operator when using Enigma, and identified a potential mistake that could greatly aid the codebreakers.
At the start of each day, the operator would set the "ring settings" on the Enigma rotors; that is, the position of the ring of letters (or numbers) around the rotor. The ring settings were taken from a codebook
, but changed daily, and had to be altered at the start of each day before any messages could be sent. The ring settings could be adjusted before or after inserting the rotors into the machine. Herivel assumed that at least some of the operators would adjust them after. In the normal course of things, adjusting the rotors inside the machine would likely leave the correct ring setting at the top, or near the top, of the rotors.
Furthermore, for each message, the sending operator would follow a standard procedure. He would first select a starting position for the rotors, the ground setting : GKX, for example. He would then use Enigma with the rotors set to GKX to encrypt a second starting position, the message setting, which he might choose to be RTQ; RTQ might encrypt to LLP. (Before May 1940 the message setting would be repeated then encrypted, but this makes no difference to Herivel's observation.) The operator would then turn his rotors to RTQ and encrypt the actual message. Included in the preamble to the message, unencrypted, would be the ground setting (GKX) as well as the encrypted message setting (LLP). A receiving Enigma operator could use this information to recover the message setting and then decrypt the message.
The ground setting (GKX in the above example) should have been chosen at random, but Herivel reasoned that if an operator were lazy, or in a hurry, or otherwise under pressure, he might simply use whatever rotor setting was currently showing on the machine. If this was the first message of the day, and the operator had set the ring settings with the rotors already inside the machine, then the rotor position currently showing on the machine could well be the ring setting itself, or else very close to it. (If this situation occurred in the above example, then GKX would be the ring setting, or very close to it). Moreover, the ground setting was sent unencrypted in the preamble to the message, which could then be easily spotted by the codebreakers at Bletchley Park.
The Herivel tip suggested that there would be a cluster of entries close together, such as the cluster around GKX in the above example. This would narrow the options for the ring settings down from 17,576 (263) to a small set of possibilities, perhaps 6–30, which could be tested individually.
The effect predicted by Herivel was not immediately apparent in the Enigma traffic, however, and Bletchley Park relied chiefly on a different technique to get into Enigma: the method of "perforated sheets
", which had been passed on by Polish cryptologists. The situation changed on 1 May 1940, when the Germans changed their indicating procedure, rendering the perforated sheets obsolete. Hut 6 was suddenly unable to decrypt Enigma.
Fortunately for the codebreakers, the pattern predicted by the Herivel tip began to manifest itself. David Rees spotted a cluster in the indicators, and on 22 May an Air Force message sent on 20 May was decoded, the first since the change in procedure. The Herivel tip was used in combination with another class of operator mistake, known as "cillies", in order to solve the settings and decipher the messages. This method was used for several months until specialised codebreaking machines designed by Alan Turing
, the so-called "bombe
s", were ready for use.
Gordon Welchman speculates that the Herivel tip was a vital part of breaking Enigma at Bletchley Park, writing, "If Herivel had not been recruited in January 1940, who would have thought of the Herivel tip, without which we whould have been defeated in May 1940 — unable to maintain continuity until the bombes began to arrive many months later? Let there be no misconceptions about this last point. Loss of continuity would, at all stages, have been very serious, if not disastrous."
Because of the importance of his contribution, Herivel was singled out and introduced to Winston Churchill
during a visit to Bletchley Park. He also taught Enigma cryptanalysis
to a party of Americans assigned to Hut 6
in an intensive two-week course. Herivel later worked in administration in the "Newmanry
", the section responsible for solving German teleprinter ciphers using machine methods such as the Colossus computer
s, as assistant to the head of the section, mathematician Max Newman
.
In 2005, researchers studying a set of Enigma-encrypted messages from World War II noted the occurrence of the Herivel tip in messages from August 1941.
, Joseph Fourier
and Christiaan Huygens. In 1978 he retired to Oxford, where he became a Fellow of All Souls College
. His books include:
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...
codebreaker
Codebreaker
Codebreaker may refer to:*A person who performs cryptanalysis*The Codebreakers, a 1967 book on history of cryptography by David Kahn*Codebreaker , a 1981 puzzle-based computer game, originally released for the Atari 2600...
at Bletchley Park
Bletchley Park
Bletchley Park is an estate located in the town of Bletchley, in Buckinghamshire, England, which currently houses the National Museum of Computing...
.
As a codebreaker concerned with Cryptanalysis of the Enigma
Cryptanalysis of the Enigma
Cryptanalysis of the Enigma enabled the western Allies in World War II to read substantial amounts of secret Morse-coded radio communications of the Axis powers that had been enciphered using Enigma machines. This yielded military intelligence which, along with that from other decrypted Axis radio...
, Herivel is remembered chiefly for the discovery of what was soon dubbed the Herivel tip or Herivelismus. The "tip" was an insight into the habits of German operators of the Enigma cipher machine
Enigma machine
An Enigma machine is any of a family of related electro-mechanical rotor cipher machines used for the encryption and decryption of secret messages. Enigma was invented by German engineer Arthur Scherbius at the end of World War I...
that allowed Bletchley Park to easily deduce part of the daily key
Key (cryptography)
In cryptography, a key is a piece of information that determines the functional output of a cryptographic algorithm or cipher. Without a key, the algorithm would produce no useful result. In encryption, a key specifies the particular transformation of plaintext into ciphertext, or vice versa...
. For a brief but critical few months from May 1940, the Herivel tip in conjunction with "cillies" (another class of operator error) was the main technique used to solve Enigma.
Herivel wrote books and articles on Isaac Newton
Isaac Newton
Sir Isaac Newton PRS was an English physicist, mathematician, astronomer, natural philosopher, alchemist, and theologian, who has been "considered by many to be the greatest and most influential scientist who ever lived."...
, Joseph Fourier
Joseph Fourier
Jean Baptiste Joseph Fourier was a French mathematician and physicist best known for initiating the investigation of Fourier series and their applications to problems of heat transfer and vibrations. The Fourier transform and Fourier's Law are also named in his honour...
, Christiaan Huygens, and an autobiographical account of his work at Bletchley Park, Herivelismus.
Recruitment to Bletchley
John Herivel was born in BelfastBelfast
Belfast is the capital of and largest city in Northern Ireland. By population, it is the 14th biggest city in the United Kingdom and second biggest on the island of Ireland . It is the seat of the devolved government and legislative Northern Ireland Assembly...
, and attended Methodist College Belfast
Methodist College Belfast
Methodist College Belfast , styled locally as Methody, is a voluntary grammar school in Belfast, Northern Ireland, one of eight Northern Irish schools represented on the Headmasters' and Headmistresses' Conference, and is a member of the Independent Schools Council...
from 1924 to 1936. In 1937 he was awarded a Kitchener Scholarship to study mathematics at Sidney Sussex College, Cambridge
Sidney Sussex College, Cambridge
Sidney Sussex College is a constituent college of the University of Cambridge in England.The college was founded in 1596 and named after its foundress, Frances Sidney, Countess of Sussex. It was from its inception an avowedly Puritan foundation: some good and godlie moniment for the mainteynance...
. Shortly thereafter, Herivel was recruited to Bletchley Park by his former supervisor Gordon Welchman
Gordon Welchman
Gordon Welchman was a British-American mathematician, university professor, World War II codebreaker at Bletchley Park, and author.-Education and early career:...
, head of the newly formed Hut 6
Hut 6
Hut 6 was a wartime section of Bletchley Park tasked with the solution of German Army and Air Force Enigma machine ciphers. Hut 8, by contrast, attacked Naval Enigma...
section created to solve Army and Air Force Enigma. Herivel, then aged 21, arrived at Bletchley on 29 January 1940, and was briefed on Enigma by Alan Turing
Alan Turing
Alan Mathison Turing, OBE, FRS , was an English mathematician, logician, cryptanalyst, and computer scientist. He was highly influential in the development of computer science, providing a formalisation of the concepts of "algorithm" and "computation" with the Turing machine, which played a...
and Tony Kendrick.
At the time, Hut 6 were having only limited success with the Luftwaffe
Luftwaffe
Luftwaffe is a generic German term for an air force. It is also the official name for two of the four historic German air forces, the Wehrmacht air arm founded in 1935 and disbanded in 1946; and the current Bundeswehr air arm founded in 1956....
Enigma network known as "Red". Herivel was working alongside David Rees
David Rees (mathematician)
David Rees ScD Cantab, FIMA, FRS is an emeritus professor of pure mathematics at the University of Exeter, having been head of the Mathematics / Mathematical Sciences Department at Exeter for many years....
, another Cambridge mathematician recruited by Welchman, in nearby Elmers School, testing candidate solutions and working out plugboard settings. The process was slow, however, and Herivel was determined to find a method to improve their attack, and would spend his evenings trying to think up ways to do so. One evening in the middle of February 1940 he was considering the procedures followed by a German operator when using Enigma, and identified a potential mistake that could greatly aid the codebreakers.
Operator error
Codebook
A codebook is a type of document used for gathering and storing codes. Originally codebooks were often literally books, but today codebook is a byword for the complete record of a series of codes, regardless of physical format.-Cryptography:...
, but changed daily, and had to be altered at the start of each day before any messages could be sent. The ring settings could be adjusted before or after inserting the rotors into the machine. Herivel assumed that at least some of the operators would adjust them after. In the normal course of things, adjusting the rotors inside the machine would likely leave the correct ring setting at the top, or near the top, of the rotors.
Furthermore, for each message, the sending operator would follow a standard procedure. He would first select a starting position for the rotors, the ground setting : GKX, for example. He would then use Enigma with the rotors set to GKX to encrypt a second starting position, the message setting, which he might choose to be RTQ; RTQ might encrypt to LLP. (Before May 1940 the message setting would be repeated then encrypted, but this makes no difference to Herivel's observation.) The operator would then turn his rotors to RTQ and encrypt the actual message. Included in the preamble to the message, unencrypted, would be the ground setting (GKX) as well as the encrypted message setting (LLP). A receiving Enigma operator could use this information to recover the message setting and then decrypt the message.
The ground setting (GKX in the above example) should have been chosen at random, but Herivel reasoned that if an operator were lazy, or in a hurry, or otherwise under pressure, he might simply use whatever rotor setting was currently showing on the machine. If this was the first message of the day, and the operator had set the ring settings with the rotors already inside the machine, then the rotor position currently showing on the machine could well be the ring setting itself, or else very close to it. (If this situation occurred in the above example, then GKX would be the ring setting, or very close to it). Moreover, the ground setting was sent unencrypted in the preamble to the message, which could then be easily spotted by the codebreakers at Bletchley Park.
Exploiting the tip
The next day, Herivel's colleagues agreed that his idea was a possible way into Enigma. Hut 6 began looking for the effect predicted by the Herivel tip, and arranged to have the first messages of the day from each transmitting station to be sent to them early. They plotted the indicators in a grid termed a "Herivel square", an example of which is shown below. The rows and columns of the grid are labelled with the alphabet. Each ground setting received would be entered into the grid by finding the column corresponding to the first letter, the row corresponding to the second letter, and entering the third letter into the cell where the row and column intersected. For example, GKX would be recorded by entering a X in the cell in column G and row K.The Herivel tip suggested that there would be a cluster of entries close together, such as the cluster around GKX in the above example. This would narrow the options for the ring settings down from 17,576 (263) to a small set of possibilities, perhaps 6–30, which could be tested individually.
The effect predicted by Herivel was not immediately apparent in the Enigma traffic, however, and Bletchley Park relied chiefly on a different technique to get into Enigma: the method of "perforated sheets
Perforated sheets
The method of Zygalski sheets was a cryptologic technique used by the Polish Cipher Bureau before and during World War II, and during the war also by British cryptologists at Bletchley Park, to decrypt messages enciphered on German Enigma machines....
", which had been passed on by Polish cryptologists. The situation changed on 1 May 1940, when the Germans changed their indicating procedure, rendering the perforated sheets obsolete. Hut 6 was suddenly unable to decrypt Enigma.
Fortunately for the codebreakers, the pattern predicted by the Herivel tip began to manifest itself. David Rees spotted a cluster in the indicators, and on 22 May an Air Force message sent on 20 May was decoded, the first since the change in procedure. The Herivel tip was used in combination with another class of operator mistake, known as "cillies", in order to solve the settings and decipher the messages. This method was used for several months until specialised codebreaking machines designed by Alan Turing
Alan Turing
Alan Mathison Turing, OBE, FRS , was an English mathematician, logician, cryptanalyst, and computer scientist. He was highly influential in the development of computer science, providing a formalisation of the concepts of "algorithm" and "computation" with the Turing machine, which played a...
, the so-called "bombe
Bombe
The bombe was an electromechanical device used by British cryptologists to help decipher German Enigma-machine-encrypted signals during World War II...
s", were ready for use.
Gordon Welchman speculates that the Herivel tip was a vital part of breaking Enigma at Bletchley Park, writing, "If Herivel had not been recruited in January 1940, who would have thought of the Herivel tip, without which we whould have been defeated in May 1940 — unable to maintain continuity until the bombes began to arrive many months later? Let there be no misconceptions about this last point. Loss of continuity would, at all stages, have been very serious, if not disastrous."
Because of the importance of his contribution, Herivel was singled out and introduced to Winston Churchill
Winston Churchill
Sir Winston Leonard Spencer-Churchill, was a predominantly Conservative British politician and statesman known for his leadership of the United Kingdom during the Second World War. He is widely regarded as one of the greatest wartime leaders of the century and served as Prime Minister twice...
during a visit to Bletchley Park. He also taught Enigma cryptanalysis
Cryptanalysis
Cryptanalysis is the study of methods for obtaining the meaning of encrypted information, without access to the secret information that is normally required to do so. Typically, this involves knowing how the system works and finding a secret key...
to a party of Americans assigned to Hut 6
Hut 6
Hut 6 was a wartime section of Bletchley Park tasked with the solution of German Army and Air Force Enigma machine ciphers. Hut 8, by contrast, attacked Naval Enigma...
in an intensive two-week course. Herivel later worked in administration in the "Newmanry
Newmanry
The Newmanry was a section at Bletchley Park, the British codebreaking station during World War II. Its job was to develop and employ machine methods in Cryptanalysis of the Lorenz cipher. The Newmanry was named after its founder and head, Max Newman...
", the section responsible for solving German teleprinter ciphers using machine methods such as the Colossus computer
Colossus computer
Not to be confused with the fictional computer of the same name in the movie Colossus: The Forbin Project.Colossus was the world's first electronic, digital, programmable computer. Colossus and its successors were used by British codebreakers to help read encrypted German messages during World War II...
s, as assistant to the head of the section, mathematician Max Newman
Max Newman
Maxwell Herman Alexander "Max" Newman, FRS was a British mathematician and codebreaker.-Pre–World War II:Max Newman was born Maxwell Neumann in Chelsea, London, England, on 7 February 1897...
.
In 2005, researchers studying a set of Enigma-encrypted messages from World War II noted the occurrence of the Herivel tip in messages from August 1941.
After World War II
After the end of the war, Herivel taught mathematics in a school for a year, but he found he could not handle the "rumbustious boys". He then lectured at Queen's University Belfast, where he was a reader in the History and Philosophy of Science.He published books and articles on Isaac NewtonIsaac Newton
Sir Isaac Newton PRS was an English physicist, mathematician, astronomer, natural philosopher, alchemist, and theologian, who has been "considered by many to be the greatest and most influential scientist who ever lived."...
, Joseph Fourier
Joseph Fourier
Jean Baptiste Joseph Fourier was a French mathematician and physicist best known for initiating the investigation of Fourier series and their applications to problems of heat transfer and vibrations. The Fourier transform and Fourier's Law are also named in his honour...
and Christiaan Huygens. In 1978 he retired to Oxford, where he became a Fellow of All Souls College
All Souls College, Oxford
The Warden and the College of the Souls of all Faithful People deceased in the University of Oxford or All Souls College is one of the constituent colleges of the University of Oxford in England....
. His books include: