“Fifty Years of Mathematical Cryptanalysis (1937-1987),” by Glenn F. Stahly, was just declassified—with a lot of redactions—by the NSA. I have not read it yet. If you find anything interesting in the document, please tell us about it in the comments.

Really interesting research into the structure of prime numbers. Not immediately related to the cryptanalysis of prime-number-based public-key algorithms, but every little bit matters.