In the 1940s and 50s, as technology raced forwards and the Cold War intensified, many states came to rely on encryption machines to keep their secrets safe.

But what if the founder of a leading code-machine company gave the US National Security Agency secret access to their best machines - machines they were selling to states across the world?

Gordon Corera reveals new evidence of a secret 'gentlemen's agreement', and examines its implications at the height of the Cold War.

With Richard Aldrich, John Alexander, James Bamford, Stephen Budiansky, David Easter, Paul Reuvers, Scott Shane, David Sherman, Betsy Smoot

PRODUCER: PHIL TINLINE. Show less