Musical Cryptography

Cryptologia vol. 3, n. 4, Oct., 1979 © the estate of eric sams

Also in Grove 1980 ("Cryptography, Musical")

Cryptography (“secret writing”) includes any method of masking a message. Sometimes the act of communication is itself concealed, for example by the use of invisible ink. More commonly, an overt message is disguised by code or cipher. In code an arbitrary assemblage of letters or numbers is assigned some specific meaning, or an ordinary word or phrase may be allotted some quite different significance. In cipher, the letters of a message are systematically transformed, either by changing their order or by replacing them with other letters or symbols. Both code and cipher principles can facilitate communications as well as conceal them, as for example in the Morse code (strictly a cipher) and in the invention of artificial languages. All these procedures are akin to some aspects of music. Thus “key” is a basic common concept, while pitch and rhythm have evident semantic application. Indeed, music has often been conceived and described as a communication intelligible only to the initiated, which is precisely what language-structures in general and cryptograms in partic­ular are designed to be.

   Many cryptologists have been notable musicians. Among composers, Tartini, Michael Haydn, Schumann and Elgar are known to have been interested in cryptog­raphy. There is some evidence (e.g. Kahn, 1967, p.563) that the two abilities are positively correlated. The connection was also recognized and used in World War II by the British crypto-analytic service, candidates for which were asked among other things whether they could read an orchestral score. It is not surprising, then, that musical symbols or ideas should have been used in cryptography and allied disciplines from the earliest times, nor that quasi-cryptographic ideas should have been freely used in music. This article considers those separate areas in turn, dealing with each in chronological order, and than in conclusion discusses their occasional overlap.

1. Cryptography using musical ideas and symbols. 2. Other commu­nication systems using musical symbols. 3. Music using cryptographic and related concepts. 4. Conclusion.

1. Cryptography using musical ideas and symbols

The most obvious method, the assignment of letters to individual notes of music, seems to have been the earliest and has certainly remained the commonest. The late 15th-century manuscript Rules for Carrying on a Secret Correspondence by Cipher (GB-Lbl Sloane 351, f.15b) describes a musical cipher. Symbols for 24 letters and the word `et' are formed by using five different pitches on a three-line staff and altering the stem directions and note values. The five vowels are represented as in ex.1.

As an illustration, the scribe has spelt out in his music-cipher the words “In nomine summe et individue trinitatis hoc opus incipio”. The earliest documented system thereafter seems to be the analogous cipher used about 1560 by Philip II of Spain. This begins as in ex.2

and continues similarly with different note values. By the end of the 16th century some very complex systems were in practical use. Thus the papal cryptographic service about 1596 used a music-cipher of nine different pitches each variable in eight ways, yielding a possible 72 symbols. Such prolifer­ation is over-elaborate, and the simpler 11 x 2 system published by Giovanni Porta (c1600, in later editions of his seminal work on cryptography) found more general favour (ex.3).

   Many other possible uses of musical symbols were exploited by cryptographers. In 1596 Porta described a method of communication whereby a beleaguered city could send messages by ringing bells in a prearranged permutation, for example one bell once = A, twice = B, thrice = C; a second bell once = D; and so on. By 1650 Athanasius Kircher had transferred this idea to the orchestra, by allotting up to four successive notes among six instruments; thus one note from the first instrument would mean the letter A, two notes B, and so on. In 1685 Friderici proposed a number of novel and ingenious music-ciphers (such as ex.4).

Nor were the visual aspects of music neglected; thus a 17th-century manuscript (Lbl Add.45850M) when folded spells out a message, suppos­edly to Charles II, with the stems and tails of notes.

  In general the cryptographic textbooks and source-books continued to describe some form of Porta's basic table (ex.3), which recurs in readily recognizable adapta­tions throughout the 16th and 17th centuries (Davies, 1967). Between 1620 and 1685 it appeared in five major works published in England, Germany and Italy (Schwen­ter, Godwin, Kircher, Schott, Friderici). Telemann may well have been referring to it when he wrote in the oratorio Der Tag des Gerichts of having been offered instruction in a secret method of “discovering by means of music the dealings of ambassadors and generals, and conveying orders to them”.

   The Porta system evolved with music history. A specimen in the Foreign Office archives from about 1750 uses crotchets and quavers with treble and bass clefs (Schooling, 1896). Another, suggested by Philip Thicknesse in 1772, uses crotchets and minims with treble clef and key signature for extra authenticity. In the late 18thand early 19th centuries the system appears in textbooks by Guyot in France, Hooper in England and Klüber in Germany, in the form of a cipher-wheel on which the notes and corresponding letters are written round in two circles, one fixed and one movable. This device, of vital importance in the history of general cryptography (cf Kahn, 1967, pp.128-9) permits frequent resetting, thus baffling the hostile analyst. In these sources also the cipher further evolves, in the same interest, towards the random allocation of cipher letters to musical notes, the occasional representation of one letter by a two-note group, and in general a policy of analogy with real music, at least in appearance (for which purpose Klüber recommended the addition of sharps and flats). This had always seemed desirable for cryptographic reasons. Thus the papal encipherers had added to their music-cipher messages an ostensibly relevant liturgical text, so as to avert suspicion. In the later 18th and early 19th centuries the possibility of combining real cipher with real music was the subject of lively experiment and debate (‘Cipher’, Rees's Cyclo­paedia, 1819-20). A notable contribution was made by Michael Haydn who (according to his biographers, 1808) invented an elaborate music-cipher of his own (ex.5) presumably for communication purposes but perhaps for composition as well.

At least it strikingly foreshadows cipher systems later used as compositional devices (see ex.10 below); and it may even have been designed (e.g. in its treatment of modified vowels) to yield results which were not too unlike real music. But it remained a private initiative. The only documented contemporary use of music-cipher in practice, in the French diplomatic service (correspondence between the Duke of Havre and the Duke of Lorges, GB-Lbl Add.32259, f.180v), relies on a Porta-type system which is neither convincing musically nor secure cryptographically. This use continued as late as 1800. Nor was the type entirely extinct in the 20th century; the first solved intercept of the New York City Police Department (“Codes are Fragile”, 1952) was a series of melodic lines in the treble clef which turned out to be a note-for-figure encipherment of illegal wagers – furnished with occasional accents and pauses in an optimistic attempt at verisimilitude.

2. Other communication systems using musical symbols.

Meanwhile, on a different (not strictly cryp­tographic) level, musical sounds or symbols had been considered as the basis for more general semantic systems and structures. One pioneer was Bishop Wilkins, who suggested (1641) that the ordinary notes of a musical instrument might be used to express not only letters and words but things and notions, so that “there might be such a general language as should be equally speakable by all nations and peoples”. Leibniz (c1678) put forward a similar suggestion for an artificial language consisting solely of tones and intervals (Couturat, 1903). There must also have been practical research and experiment in this area, for in 1800 (as Klüber recorded, 1809) pupils at a school for the blind in Paris were `reading' phrases played on the violin. The (unspecified) techniques used may have been a Porta-type system extended for communication purposes (as by Bertini, 1811). But they were more likely to have been precursors of the ideas later developed by Jean-Francois Sudre (1787-1862), whose pupils could also converse with him via the violin. By 1817 he had constructed a complete artificial language, in which any seven different symbols could be combined five at a time, with variations of order and stress. The seven sol-fa syllables or pitches formed one obvious basis of his system, which incorporated such quasi-musical ideas as the use of “domisol” (i.e. the perfect triad) to mean “God” and its retrograde form to mean “Satan”. Similarly “sollasi” means “ascend” and “silasol” “descend”. The idea was officially welcomed in its day as having potential practical value; but it found no lasting application, and was in effect superseded by the invention of the Morse code. With the demise of Sudre's system the last serious attempt to exploit purely musical resources for purely linguistic purposes came to an end.