Great Cipher
Encyclopedia
In the history of cryptography
, the Great Cipher or Grand Chiffre was a nomenclator cipher developed by the Rossignols
, several generations of whom served the French Crown as cryptographers. The Great Cipher was excellent of its class and so was given this name; it was reputed to be unbreakable. Modified forms were in use by the French Peninsular army until the summer of 1811, and after it fell out of current use, the mostly diplomatic messages in the French archives were entirely unreadable.
, controlled by the Huguenot
s and surrounded by the French army. The letter told that the Huguenots would not be able to hold onto the city for much longer, and by the end of the day Rossignol had successfully deciphered it. The French returned the letter with the deciphered message, forcing the Huguenots to surrender. He and his son, Bonaventure Rossignol, were soon appointed to prominent roles in the court.
Together, the two devised a code so strong it baffled cryptanalysts for centuries. Commandant Étienne Bazeries
managed to break the cipher around 1893 over a period of three years, realizing that each number stood for a French
syllable rather than single letters as traditional codes did. He guessed that a particular sequence of repeated numbers, 124-22-125-46-345, stood for les ennemis ("the enemies") and from that information was able to unravel the entire cipher.
town of Cuneo
but instead fled, fearing the arrival of the Austria
ns, and consequently put in serious danger the success of the entire French campaign in Piedmont
. The letter said:
The "330" and "309" codegroups appeared only once in the correspondence, so it is impossible to confirm what they stand for. Bazeries verified General Bulonde was disgraced and removed from command, so he reasoned 330 and 309 stood for masque and a full stop. However, none of the cipher variants used in the Iron Mask period included masque, an unlikely word to include in the cipher's small repertory.
, some number sets were "nulls" meant to be ignored by the intended receipt. Others were traps, including a codegroup that meant to ignore the previous codegroup.
As a nomenclator cipher, the Great Cipher replaced the names of key generals such as Auguste de Marmont, references to les ennemis, and other sensitive terms with homophonic substitutions
. Code sheets included alternative digits to modify the gender or letter case, so the rules of French composition held true to encryptions as well. Since e is the most commonly used letter in French, the Cipher typically allocated the most code numbers to writing this vowel: in one nomenclature, 131 out of 711 code numbers stood for e.
History of cryptography
The history of cryptography begins thousands of years ago. Until recent decades, it has been the story of what might be called classic cryptography — that is, of methods of encryption that use pen and paper, or perhaps simple mechanical aids...
, the Great Cipher or Grand Chiffre was a nomenclator cipher developed by the Rossignols
Rossignols
The Rossignols, a family of French cryptographers and cryptanalysts, included:* Antoine Rossignol * Bonaventure Rossignol* Antoine-Bonaventure RossignolThe family name meant "nightingale" in French...
, several generations of whom served the French Crown as cryptographers. The Great Cipher was excellent of its class and so was given this name; it was reputed to be unbreakable. Modified forms were in use by the French Peninsular army until the summer of 1811, and after it fell out of current use, the mostly diplomatic messages in the French archives were entirely unreadable.
Historical background
Antoine Rossignol's cryptographic skills became known when in 1626 an encrypted letter was taken from a messenger leaving the city of RéalmontRéalmont
Réalmont is a commune in the Tarn department in southern France.-References:*...
, controlled by the Huguenot
Huguenot
The Huguenots were members of the Protestant Reformed Church of France during the 16th and 17th centuries. Since the 17th century, people who formerly would have been called Huguenots have instead simply been called French Protestants, a title suggested by their German co-religionists, the...
s and surrounded by the French army. The letter told that the Huguenots would not be able to hold onto the city for much longer, and by the end of the day Rossignol had successfully deciphered it. The French returned the letter with the deciphered message, forcing the Huguenots to surrender. He and his son, Bonaventure Rossignol, were soon appointed to prominent roles in the court.
Together, the two devised a code so strong it baffled cryptanalysts for centuries. Commandant Étienne Bazeries
Étienne Bazeries
Étienne Bazeries was a French military cryptanalyst active between 1890 and the First World War. He is best known for developing the "Bazeries Cylinder", an improved version of Thomas Jefferson's cipher cylinder. It was later refined into the US Army M-94 cipher device. Historian David Kahn...
managed to break the cipher around 1893 over a period of three years, realizing that each number stood for a French
French language
French is a Romance language spoken as a first language in France, the Romandy region in Switzerland, Wallonia and Brussels in Belgium, Monaco, the regions of Quebec and Acadia in Canada, and by various communities elsewhere. Second-language speakers of French are distributed throughout many parts...
syllable rather than single letters as traditional codes did. He guessed that a particular sequence of repeated numbers, 124-22-125-46-345, stood for les ennemis ("the enemies") and from that information was able to unravel the entire cipher.
The Man in the Iron Mask
In one of the encrypted letters between Louis XIV and his marshal Nicolas de Catinat appeared a possible solution to the mystery of The Man in the Iron Mask. The letter concerned a general named Vivien de Bulonde who was to attack the ItalianItaly
Italy , officially the Italian Republic languages]] under the European Charter for Regional or Minority Languages. In each of these, Italy's official name is as follows:;;;;;;;;), is a unitary parliamentary republic in South-Central Europe. To the north it borders France, Switzerland, Austria and...
town of Cuneo
Cuneo
Cuneo is a city and comune in Piedmont, Northern Italy, the capital of the province of Cuneo, the third largest of Italy’s provinces by area...
but instead fled, fearing the arrival of the Austria
Austria
Austria , officially the Republic of Austria , is a landlocked country of roughly 8.4 million people in Central Europe. It is bordered by the Czech Republic and Germany to the north, Slovakia and Hungary to the east, Slovenia and Italy to the south, and Switzerland and Liechtenstein to the...
ns, and consequently put in serious danger the success of the entire French campaign in Piedmont
Piedmont
Piedmont is one of the 20 regions of Italy. It has an area of 25,402 square kilometres and a population of about 4.4 million. The capital of Piedmont is Turin. The main local language is Piedmontese. Occitan is also spoken by a minority in the Occitan Valleys situated in the Provinces of...
. The letter said:
- His Majesty knows better than any other person the consequences of this act, and he is also aware of how deeply our failure to take the place will prejudice our cause, a failure which must be repaired during the winter. His Majesty desires that you immediately arrest General Bulonde and cause him to be conducted to the fortress of Pignerole, where he will be locked in a cell under guard at night, and permitted to walk the battlement during the day with a 330 309.
The "330" and "309" codegroups appeared only once in the correspondence, so it is impossible to confirm what they stand for. Bazeries verified General Bulonde was disgraced and removed from command, so he reasoned 330 and 309 stood for masque and a full stop. However, none of the cipher variants used in the Iron Mask period included masque, an unlikely word to include in the cipher's small repertory.
Technical nature of the Cipher
The basis of the code cracked by Bazeries was a set of 587 numbers that stood for syllables. There were other variations, and Louis XIV's overseas ministers were sent different code sheets that encrypted not only syllables but also letters and words. To counter frequency analysisFrequency analysis
In cryptanalysis, frequency analysis is the study of the frequency of letters or groups of letters in a ciphertext. The method is used as an aid to breaking classical ciphers....
, some number sets were "nulls" meant to be ignored by the intended receipt. Others were traps, including a codegroup that meant to ignore the previous codegroup.
As a nomenclator cipher, the Great Cipher replaced the names of key generals such as Auguste de Marmont, references to les ennemis, and other sensitive terms with homophonic substitutions
Substitution cipher
In cryptography, a substitution cipher is a method of encryption by which units of plaintext are replaced with ciphertext according to a regular system; the "units" may be single letters , pairs of letters, triplets of letters, mixtures of the above, and so forth...
. Code sheets included alternative digits to modify the gender or letter case, so the rules of French composition held true to encryptions as well. Since e is the most commonly used letter in French, the Cipher typically allocated the most code numbers to writing this vowel: in one nomenclature, 131 out of 711 code numbers stood for e.