“Correspondences Regarding Cryptography between John Nash and the NSA [Typeset Version]”, 2012-02-20 (; backlinks; similar):
In 1955, well-known mathematician John Nash was in correspondence with the United States National Security Agency. In these letters, Nash proposes a novel enciphering scheme. He also sets forth an important cryptographic principle that now underpin modern computational complexity theory and cryptography. In particular, he proposes a natural definition for “[security] in a practical sense”—that exponential computational effort is required for an enemy to recovery a secret key. Nash further conjectures that this property holds for any suitable enciphering mechanism.
These correspondences, recently declassified by the NSA1, have been transcribed and typeset in this document. [Typeset by Mike Rosulek: Department of Computer Science, University of Montana, mikero@cs.umt.edu]