# Cryptography in the NTM (Prague)

Photography by Carlos Dorce

I hope this is my last post about the NTM in Prague after talking about the astronomical instruments and Kircher’s Organum Mathematicum! Opposite the astronomical exhibition, there is another about secrets and adults and children can play with the cryptography (if they know the Czec language!):

Ché Guevara used a number code when communicating with Fidel Castro. He transposed each letter in the text to a number […]. He then wrote those numbers one behind the other. Below that line he wrote a second line of numbers, known only to him and Castro, which was used only once. He then added both lines, number per number, and below each set of numbers he wrote (the last digit of) the sum. This give a third line of numbers. Only that row was transmitted. When Castro subtracted the second line from the third, he had the first line as the result.

The Ché method cannot be cracked because the key (the second line of numbers) is random, as long as the message, is only used once.

One of the oldest methods for hidding a message is the Ribbon Code:

The code system of winding ribbons around a shaft was already known to the Greeks of the seventh century BC. The generals of Sparta received a staff in deep secrecy, of which the other half was kept by the magistrates of the city. Messages were written on a leather belt.

The Greek called such a stick a scytale and code experts today still use that name. The scytale is an example of a ‘transposition code’, a code in which the letters of a text are mixed up according to a specified recipe. The drawback of a scytale is that the spy can already guess from the ribbons which coding technique was used. It is then only a matter of patience to find the right diameter of the shaft. Gabrielle Petit, a heroine of the Belgian resistance during World War I, passed messages on silk ribbons, which she camouflaged as part of her clothes.

Photography by Carlos Dorce

The Caesar code is also explained:

Photography by Carlos Dorce

The French cardinal Richelieu (1585-1642), a famous and powerful intrigant, fully used this technique to stay in contact with his agents and spies. They were each given a mask, to put over his letters.

In this method, you and your partner each have the same grid with holes. You write a message in the holes, and afterwards you fill in the remaining space with innocent text. This technique is known as the ‘Cardan grille’ after Girolamo Cardano, of Cardan joint fame, who invented the grille in 1550. It is very difficult to crack.

Photography by Carlos Dorce

Finally, a space for the Enigma machine:

The Enigma was the German top coding machine during World War II. The Germans thought their messages to be uncrackable. Which would indeed have been the case, if they operators hadn’t made procedural mistakes and the British hadn’t secured a code book. The mathematical genius Alan Turing designed the first automatic calculators to do the enormous amount of computations needed to check all possibilities. It is assumed Turing and his crew shortened the war with two years.

Photography by Carlos Dorce

LocationNational Technical Museum in Prague (map)

# Turing in the Science Museum

Photography by Carlos Dorce

Today is my birthday and I’m in London! My wife, my son, my daughter and me have decided to go to the Science Museum and we have found an interesting exhibition about Alan Turing:

The Second World War was not just fought with bombs and shells. It was a war of electronic whispers and secret radio signals snatched from the ether.

At Bletchey Park, Buckinghamshire, thousands of men and women laboured night and day to crack these coded radio messages which held Germany’s most secret plans. One of these codebreakers was Alan Turing.

But Turing was not just a codebreaker. Born 100 years ago, the British mathematician was also a philosopher and computing pioneer who grappled with some of the fundamental problems of life itself. Yet his own life was cut tragically short. In 1954 he was found dead, poisoned by cyanide. He was 41.

Throughout his life, Turing broke the codes of science and society. His ideas helped shape the modern world – but it was a world he did not live to see. This is his story.

After the Second World War, Alan Turing as asked to put his theories and experience into action by developing a ground-breaking electronic computer at the government’s National Physical Laboratory. His first specifications were written in 1945.

Following administrative delays, Turing left the project in 1948, but a trial version (known as Pilot ACE) was completed in 1950. It is now the most significant artefact in existence.

Yet the Pilot ACE computer was more than just a trial. It was used for several years by a variety of external customers desperate to employ its computing power. It also became a public celebrity, referred to as Turing’s ‘electronic brain’.

(Very bad) Photography by Carlos Dorce

So Turing was the man who broke Enigma and this machine is also shown in the exhibition:

Photography by Carlos Dorce

Enigma machines were first introduced in the 1920s for keeping commercial messages secret. An Enigma machine was used at both the transmitting and the receiving end of the message.

Senders typed their messages on the keyboard. Each typed letter was encrypted by passing an electrical signal through a plug-board and rotors, causing a different letter to light up. These new letters formed a secure message, ehich could be transmitted by radio to the recipient.

At the receiving end, the message was decrypted using an Enigma machine that had been set up initially in exactly the same way as the sending machine.

Soon after their introduction, government institutions and the military began to use modified Enigma machines for their secret communications, believing nobody would be able to break the cipher system. But this was what Alan Turing and his colleagues managed to do.

Alan Turing worked at Bletchey and he developed sophisticated decryption processes and devised the machines called ‘bombes’ that could break the code on an industrial scale. Some 200 bombes were built at a secret facility nearby. The exhibition had some pictures about the bombs and these two wheels from a bomb machine, c. 1940:

Photography by Carlos Dorce

Next to Turing’s bombs and computers we can also see these two pioneer calculating machines:

Photography by Carlos Dorce

The right one is a mechanical logic machine by William Stanley Jevons (1869) and the other is an electrical logic machine by Dietrich Pronz and Wolfe Mays (1949).

We have some personal aspects of this important man too. For example, the exhibition points to the fact that in 1927 Turing began a close friendship with a boy at this school, Christopher Morcom. In 1930 Morcom died from tuberculosis, aged 18, and Turing wrote a short essay expressing his belief that the human spirit can live outside the body.

Photography by Carlos Dorce

The exhibition also shows this calculating machine used at the Scientific Computer Service in 1939:

Photography by Carlos Dorce

I didn’t know that questions like…

What will be the position of the Moon in A.D.2000? How would you know the right direction in which to point an anti-aircraft gun?

were posed in a 1942 newspaper articleabout the Scientific Computing Service. Before Turing’s computer, ‘computers’ were human and usually women. In fact, in 1936 Turing wrote an article which was the theoretical basis for today’s computers because he imagined a machine that could compute any problem.

In 1948, Alan Turing moved to Manchester University to work on a ground-breaking stored-program computer developing mathematical theories of morphogenesis (growth and patterns in animals and plants). In those years he began a relationship with Arnold Murray and in 1952 Turing was arrested under anti-homosexuality legislation. Given a choice of imprisonment or a one-year course of female hormones, he opted for the latter. It seems that he couldn’t stand that kind of experiment and he committed suicide.

Photography by Carlos Dorce

Location: Science Museum in London (map)

# Cryptography in Peter and Paul Fortress

Encrypting code
Photography by Carlos Dorce

After visiting the exhibition about Leonardo da Vinci and the Russian Emperors and Empresses’ tombs in the church, I decided to finish my visit to Peter and Paul Fortress entering in the jail. All the cells of the jail have posters next to their doors with explanations about famous Russian people who were there. Of course I didn’t read all the posters but there was one which aroused my interest. The prisoners were isolated and they couldn’t talk to each other. So they developed a cryptographic code to communicate:

Tapping was the only way of communication between prisoners in single cells. They used so called “prison alphabet”. Letters in alphabetical order were accumulated in a table of six lines and five columns. Each letter was tapped in two steps, number of a line, then number of a column. Prisoners “spoke” tapping the floor, walls or legs of a bedstead.

This encrypting method is also known as Polybius square. Polybius was a Greek historian who lived in the IInd century BC and he is supposed to have invented the method.

Location: Peter and Paul Fortress (map)