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Hello, in October 1586 in the forbidding hall of Fotheringay Castle, Mary Queen

of Scots was on trial for her life, accused of treason and denied legal representation, she sat alone in the shadow of a vast and empty

throne belonging to her absent cousin, an arch rival Elizabeth I of England.

Walsingham, Elizabeth's principal secretary,

had already arrested and executed Mary's fellow conspirators.

Her only hope lay in the code she'd used in all her letters concerning the plot. If her cipher remained unbroken, she might yet

be saved. Not for the first time, the life of an individual and the course of history depended

on the arcane art of cryptography.

What are the origins of this secretive science?

And what links the Caesar cipher

with the complex algorithms which underpin so much of our modern age?

With me, to discuss the history of cryptography

are Simon Singh, science writer,

and author of The Code Book,

The Secret History of Codes and Code Breaking.

Lisa Jardine, Professor of Renaissance Studies at Queen Mary, and Professor Fred Piper,

Director of the Department of Information Security at Royal Holloway University of London.

Simon Singh, can you tell us how secret messages were communicated before? of the stegonography and what is that? Yeah no stegonography is something that people

don't talk about much nowadays but it's what you do is well with cryptography you hide

the message by scrambling it up so nobody can read it. It's there in front of you staring in the face

...