Tuesday 13 November 2012

Cryptography and Linear B by Manda Scott

One of the real joys of a writing life, is the ability to fall into a topic, to become immersed in the minutiae of something out of the ordinary and call it ‘work’. It is possible, even, to be paid for doing so, and then exercising one’s imagination on the product of that immersion; a fact that never ceases to amaze (and delight) me.
So it is with spies and spying.  Since the first cave family sent someone out to listen in on their neighbour’s plans for hunting woolly mammoths, spying has been part of our world, so hidden, so unspoken that it didn’t even merit the title of ‘the first profession’ although it surely was.  
Since then, almost every era has had a text that relates one way another to clandestine investigation, to codes or ciphers, starting with Sun Tzu’s ‘Art of War’ which lists the five types of spy and how they should be treated.  
The following, from Chapter 13 still seems to me a perfect distillation of espionage, it’s value and promotion: 

Knowledge of the enemy's dispositions can only be obtained from other men.
Hence the use of spies, of whom there are five classes: (1) Local spies; (2) inward spies; (3) converted spies; (4) doomed spies; (5) surviving spies.
When these five kinds of spy are all at work, none can discover the secret system. This is called "divine manipulation of the threads." It is the sovereign's most precious faculty.
Having local spies means employing the services of the inhabitants of a district.
Having inward spies, making use of officials of the enemy.
Having converted spies, getting hold of the enemy's spies and using them for our own purposes.
Having doomed spies, doing certain things openly for purposes of deception, and allowing our spies to know of them and report them to the enemy.
Surviving spies, finally, are those who bring back news from the enemy's camp.
Hence it is that which none in the whole army are more intimate relations to be maintained than with spies.
None should be more liberally rewarded. In no other business should greater secrecy be preserved.
Spies cannot be usefully employed without a certain intuitive sagacity.
They cannot be properly managed without benevolence and straightforwardness.
Without subtle ingenuity of mind, one cannot make certain of the truth of their reports.
Be subtle! be subtle! and use your spies for every kind of business.

If you allow that 'men' also equals 'women', I have yet to find a better elucidation of the nature of spies or their use. 
But the spy herself is only the first part of the chain of espionage; information is of no use if it cannot be transmitted back to those who need it most, and it's the use of codes and ciphers that seems to me most fascinating, particularly nowadays, when we conduct so many transactions over the internet, and rely on secrecy – ciphers – to keep our bank and credit card secrets secure. 
The origins of ciphers doubtless also goes back to Sun Tzu even if he was astute enough not to mention them.  Julius Caesar wrote a treatise on ciphers, which has sadly been lost to posterity – the only surviving example is a simple letter substitution cipher of the kind we all used at school where A=b, B=c and on until the alphabet wraps round and Z=a.  This isn’t enough to fill a whole book, though and there seems little doubt that the man with the military capacity to conquer Gaul will have found more complex ways of scrambling and unscrambling text than simply shifting letters one space along in a linear alphabet. 

(Image of Julius Caesar courtesy of ‘thisisbossi’ on Flickr)
Other methods of the time that did not require either party to write out the alphabet to decode the message included winding a strip of leather around a stick with (say) a hexagonal cross section. The message was written along the leather-wound stick, then the leather unwound and hidden, or perhaps used as a belt with the letters on the inside. As long as the recipient had a stick of the same diameter, then winding the belt around it would once again demonstrate the message.
Sometimes simply writing – or sending – the message in a different language was enough. We know that the Romans used Greek on occasion, believing that ‘barbarian’ tribes couldn’t read it (this was almost certainly false given that Greek was the lingua franca of the time) and in the second world war, the US successfully used teams of native Navajo speakers to produce entirely unbreakable wireless transmissions. While the statisticians of the US military cryptographic units were working out Japanese code, their counterparts were unable to penetrate the Navajo, partly because of the entirely unique language structure.
And then there’s the fascination of a code that is in an entirely different language – such as Linear B.   The story of the breaking of Linear B has been called one of the greatest archaeological decipherment of all time (Breaking the Nazi Geheimschreiber teleprinter codes in the Second World War was probably the greatest military cryptographic feat of all time, if only for the technological development of the computer that grew out of it).
Linear B is found on a series of baked clay tablets – most of them either leaf-shaped or rectangular - found in the remains of a large and complex palace at Knossos, on Crete, at the start of the twentieth century.   These were unusual for a number of reasons, but primarily because clay tablets of the time were rarely baked hard to preserve them, but usually kept ‘air dry’ so they could be soaked in water and re-used. 

(Image courtesy of Sharon Mollerus, ‘Clairity’ on Flickr)
These, however, were complete and covered in inscriptions of a kind never seen before.  They were soon sorted into three groups: ancient tablets with symbols that related (probably) to seals of office; these came from 2000 to 1650 BC.  The second group hailed from 1750 to 1450 BC and were called Linear A. The third group, Linear B, were dated from 1450 to 1375BC.   Of these, many were inventories and the numbers were easy to decipher.  The writing was a different matter: 90 separate characters existed, but none were related in any obvious way to any of the ancient languages of the region
Sir Arthur Evans, the archaeologist who found the tablets, was convinced that Linear B was a form of pre-Greek Cretan, arising from the Minoan Empire – the same civilization that gave rise to King Minos and the Minotaurs (in fact, it was suggested that the highly complex, labyrinthine palace had given rise to the Minotaur legend).

(Photo taken by flickrolf on Flickr, This is the room described by Evans as ‘The Queen’s Boudoir’)
Evans’ argument was supported by much of the Establishment and they didn’t take dissent lightly: individuals who dared suggest that the tablets might not be Minoan (and evidence of Minoan supremacy in the region at the time) frequently found their careers suffered as a result of their audacity. Still, nobody decoded the plates.

(Photo courtesy of Kiminoa on Flickr)
It took an American academic, Alice Kober, to begin to break the code. Using statistical analysis of the type that became the bread and butter of Alan Turing and the teams at Blechley Park during the war, she created tables of allied symbols: pairs of symbols which were seen together frequently.   It had been decided already that Linear B was a syllabic script – there were too many symbols to be alphabetic, and too few to be purely symbolic (as in Chinese),  thus it made sense for some pairs or groups of syllables to be allied.  Kober also found certain ‘bridging’ syllables which joined other pairs.
Sadly, Alice Kober died before she could take the next essential step in decoding the cipher, that was taken by an English architect with a fascination for Linear B, Michael Ventris.  As with many cryptographers, Ventris was an outstanding linguist: he was fluent in French and German by the time he went to school and taught himself Polish at the age of six.
Although by profession an architect, Ventris spent all of his spare time on Linear B, and began to work out which consonant/vowel combinations carried similar consonants but different vowels. By linking these together, and by discovering which of the 90 symbols represented vowels alone, he was able to discover the name of a city within the text: Knossos.  (or rather, Knosso – the final ‘s’ was missing, but in the scale of things, that was irrelevant).
Using the syllables already discovered, Amnisos and Tulissos soon fell to his statistical analysis and so the threads began to unravel.  Codebreakers at Bletchley Park said they could work for 30 hours at a stretch on a code, in the early days, when they were all done by hand; that finding one word and then another became addictive, and over-rode the need for sleep.
So it may have been with Ventris who began slowly to discern other words within the text: there was only one problem: what he had found was Greek and that meant turning over an entire archaeological theory about the nature of the ancient world: that the Minoan Empire perhaps was not supreme when it was thought to have been: that Greece was superior for longer than was known and was able to exert influence – and force a change in language – far earlier than anyone had believed.
It took another scholar, John Chadwick, who had worked as a cryptologist at Bletchley Park to complete the cycle.  Chadwick was an expert in the evolution of ancient Greek and so was able to support Ventris at a point when the Establishment might otherwise have closed against him.  Together, they decoded the script and thus the tablets – and in doing so, found out why they were baked: several of the tablets record the possibility of invasion, and outline detailed ceremonies aimed at placating gods who might repel the invaders.  It seems likely that the palace was destroyed by fire, thus baking for posterity the last words of the ancient scribes.
And the greater mass of the tablets? They were inventories, written in exhaustive detail, of the taxes paid and good traded, so that we know to the nearest pig and sheep who paid what and where and when.  If we think our own Inland Revenue are a bunch of mean minded bean counters, at least there is some consolation in knowing that they didn’t arise in the recent past. Three thousand years ago, someone was busy recording the details of one sheep in a herd of thousands, so they could tax the owner accordingly.


Simon Jones said...

Fascinating - I had not realised the Bletchley/Linear B connection.
Great scope - from Sun Zsu to the Minoans via WW2!

jongleuse said...

Completely fascinating post. I had heard about the Navajo code talkers but didn't know about the WW1 involvement. The Linear B story is so fascinating.

Manda Scott said...

The amazing thing for those of us fascinated with cryptography is that Linear A remains undeciphered...

Thanks, all


Mary Tod said...

Fascinating stuff ... have you read the book about Bletchley Park by Sinclair McKay? Also fascinating.

Katherine Langrish said...

Oh yes, Manda - I'm WAITING for Linear A. Who's working on it? Come on!