The Code Book: The Science of Secrecy from Ancient Egypt to Quantum Cryptography

In 1586, Queen Mary was put on trial for treason, accused of planning to assassinate Queen Elizabeth, Queen of England, in an attempt to take the throne for herself. Her mortal fate hung in the balance and would eventually be decided on the basis of whether or not it could be proved that she was a willing participant in the assassination plot. Those who had already been caught and declared guilty were a party of restless Catholic noblemen intent on bring the nation back to its Catholic roots; this of course necessitated the ousting of the Protestant Elizabeth.

In order to prove that Mary had been involved in the plot, the prosecution needed to show that the ciphers the conspirators had used in their plan, and which they had used in order to communicate with Mary, implicated Mary in the plot explicitly. To do this, the ciphers would have to be interpreted. The judgment of the court depended on this alone, for “if Mary’s cipher was strong enough to conceal her secrets, then there was a chance that she might survive” (18-19).

The use of ciphers in order to conceal messages and important communication dated back to the days of ancient Greece and Rome.