His “Communication Theory of Secrecy Systems”, from a few years prior, is right up there too.

https://en.m.wikipedia.org/wiki/Communication_Theory_of_Secr...

IMO Shannon does an amazing job laying out the foundational ideas behind cryptographic security in a way that is very accessible to anyone with a basic understanding of probability.

The clarity and simplicity that he achieves is especially striking when you compare his approach to what you’ll see from modern cryptographers. No offense to those guys - they’re amazing - but accessible their stuff is not.