Welcome to Saturday Night at the Movies.

I'm your host, Glenn Holland.

Tonight's film is the 2014 Historical Drama, The Imitation Game, directed by Morten Tyldum.

It Stars Benedict Cumberbatch, Keira Knightley, Matthew Goode, Rory Kinnear, Allen Leech, and Charles Dance.

The film chronicles the attempt to analyze and duplicate the Enigma machine used by the Nazis to send encrypted military orders during the Second World War.

The Enigma machine produced a new encryption each day, frustrating attempts to decipher it using traditional methods.

Alan Turing a mathematician, logician, and cryptologist is recruited by British Intelligence to join other men working on the project at Bletchley Park in Buckinghamshire.

But Turing is difficult to work with, and doesn't hesitate to demonstrate his superior intellect or to berate his fellows, even if it hinders the work of the team.

When the officers supervising Turing refuses him the funding he needs to build a machine he is designed to decipher Enigma, Turing writes to Prime Minister Winston Churchill to have himself put in charge of the project.

He fires several of his coworkers and secures new ones by placing a particularly difficult crossword puzzle in the daily newspapers.

In this way, he recruits Joan Clark a graduate in mathematics from Cambridge but her parents refuse her permission to work with men.

Turing arranges for her to live and work with the women's unit at Bletchley Park while making her own contributions to the Enigma Project.

As their work continues, the other cryptologist begin to respect Turing.

But the difficulties of building a decrypting machine and the pressures imposed by the continuation of the war take their toll on all of those engaged in the work they know is essential to an allied victory over the Nazis.

The practice of sending secret messages that could be understood by allies, but baffled enemies goes back to ancient times.

There are essentially three ways of sending secret messages.

One is to hide the intended message by some means such as the use of invisible ink.

Herodotus, a Greek historian of the fifth century BCE provides the example of a secret message tattooed on the shaved head of a slave that was concealed once his hair grew back.

A second form of secret message is the code which substitutes one word for another in a message.

Codes require a code book used by both sender and receiver.

One that theoretically includes all the words that might possibly appear in a message between them.

The third and most common method for sending secret messages is the cipher, which focuses on the individual letters used to write a message.

A cipher might transpose the letters of a message or more often substitute a different letter or symbol for each letter of the original message.

The Roman historian Suetonius, right in the early Imperial era, reports that Julius Caesar would replace each letter of a message to his generals with a letter of some fixed number of positions, say three further down the alphabet.

So A would become D, B would become E, and so on.

But obviously ciphers of this sort are easily devised and easily detected.

A common feature in daily newspapers is a substitution cipher for the reader to figure out after perusing the comics and completing the crossword puzzle.

This is because solving these ciphers is based on what we know about how our language works, linguistics, and what we know about how our system of writing works.

But for the last hundred years or so cryptography has been increasingly based on mathematics including statistics, abstract algebra, and number theory.

It has also become the work of various sorts of machines including ancestors of modern computers.

The Enigma machine had an electro mechanical rotor mechanism that randomly scrambled the letters of the alphabet.

The security of the system depended on a set of machine settings that were generally changed daily during the war based on secret key lists distributed to each receiving station in advance.

Each station had to know and use the exact settings employed by their transmitting station to successfully decrypt a message.

Based on information gathered from intelligence services, Polish cryptologists were able to produce their own version of an Enigma machine in the early 1930s.

But the Germans continued to improve the machine, and its functions, so that by the time the second World War began their military ciphers were considered unbreakable.

This was the problem faced by Alan Turing and his fellow cryptologists at Bletchley Park and the driving force behind their work.

Graham Moore's screenplay for the Imitation Game won the 2014 Academy Award for best adapted screenplay.

It was based on the 1983 biography, Alan Turing: The Enigma by Andrew Hodges, a British mathematician.

A critic who compared the film to the book wrote, "The Imitation Game takes major liberties with its source material injecting conflict where none existed, inventing entirely fictional characters, rearranging the chronology of events, and misrepresenting the very nature of Turing's work at Bletchley Park."

Some variation on this critique might be written about almost every historical drama ever filmed since a screenplay must compress actual events into a story that is both comprehensible and compelling for its audience.

This is an especially difficult task when one is dealing with characters engaged in work that involves the intricacies of higher mathematics.

Take the character of Joan Clark, for example.

She was recruited by the government code in Cipher School at Bletchley Park, not by Alan Turing, but by her former academic supervisor mathematician Gordon Welchman.

Most of her work there involved banburismus an analytic process developed by Alan Turing that used sequential conditioning probability to infer information about the likely settings of the Enigma machine greatly expediting the process of deciphering.

Hugh Alexander, played in the film by Matthew Goode, described Clark as one of the best banburismus in the section.

Alexander was himself considered the best of the banburismus at Bletchley Park.

He and I.J.

Good, played in the film by James Northcote, consider the process more of an intellectual game than a job.

Alexander said it was not easy enough to be trivial but not difficult enough to cause a nervous breakdown.

If you're not confident, you know just what Joan Clark Hugh Alexander, and Jack Good were up to at Bletchley Park, there's a good chance you have a degree in mathematics.

On the other hand, if you have only a tentative grasp of what they were doing, you'll appreciate why a screenplay might take major liberties with its source material.

Even though filmmakers might present biographical films about a mathematician like John Nash in a Beautiful Mind in 2001, or a theoretical physicist like Stephen Hawking in The Theory of Everything in 2014, the story is always more about the person rather than the intricacies of his or her work.

In the case of The Imitation Game, the story focuses very much on Alan Turing and presents the complicated business at deciphering Enigma with Turing at the center of it all.

The other people involved in that effort and the other very important intelligence work at Bletchley Park are important to the film only in relationship to Turing, its primary character.

As director Morten Tyldum said in an interview, "We wanted the movie to be emotional and passionate.

Our goal was to give you what does Alan Turing feel like?

What does his story feel like?

What did it feel like to be Alan Turing?"

Although her relationship with Turing might be romanticized in the film, Joan Clark was an important part of the story.

She became close friends with Turing soon after they met at Bletchley Park.

They shared many of the same interests and hobbies and had similar personalities.

Turing arranged their shifts so they could work together.

He proposed marriage to her in early 1941 and introduced her to his family, but broke off their engagement after a few months.

He had earlier told Clark he was gay.

She was apparently unphased by the revelation and decided he could not go through with a marriage.

In 1947, Clark met a retired army officer Lieutenant Colonel John Kenneth Ronald Murray while working at government communication headquarters.

She married him five years later.

She remained friends with Alan Turing until his death in 1954.

Turing's death is described to the film as a suicide following his chemical castration as a penalty for his homosexuality.

But there are doubts about that claim.

More than a year after the chemical castration ended, Turing ate an apple laced with cyanide.

His biographer, Andrew Hodges, believes this was a suicide based on the poison apple from the story of Snow White, Turing's favorite fairy tale.

But Jack Copeland, another authority on Turing's life and work has suggested the apple may have been contaminated by cyanide fumes from one of Turing's experiments and his death a tragic accident.

But of course, we will never know for sure.

Please join us again next week for another Saturday Night at the Movies.

I'm Glen Holland.

Goodnight.