"A Method for Obtaining Digital Signatures and Public-Key Cryptosystems", Ronald L. Rivest, Adi Shamir, and Leonard M. Adleman. PDF reprint of: CACM 21/2, pp. 120-126 » . The original paper on RSA (and the birth of Alice and Bob).
LaTeX reprint of: CACM 3/4, pp. 184-195 » . It is the original paper on Lisp. (BTW: Part II was never published.)
Reprinted from: The Bell System Technical Journal 57 no. 6, part 2 (July-August 1978), which is a revised version of: CACM 17/7, pp. 365-375 » .
Reprinted from: CACM 27/8, pp. 761-763 » .