NSA declassifies handwritten letter from Nash which anticipates P vs NP and its application to crypto in '55
The nature of this conjecture is such that I cannot prove it, even for a special type of cipher. Nor do I expect it to be proven. But this does not destroy its significance. The probability of the truth of the conjecture can be guessed at on the basis of experiencing with enciphering and deciphering.
There are so many reasons that this is amazing. John Nash’s handwriting! His lucid explanation of good security practice! His understanding of the fundamental difference between tractable and intractable computations! Circuit diagrams seemingly drawn in crayon!