What are some "must-read" papers for someone getting into Quantum Cryptography?
For an interesting starting paper, that nearly was never a paper see Stephen Wisener's paper on Conjugate Coding. This paper started off things like the BB 84. The paper is paywalled though, and a typewritten copy (with typos too,), as it was written sometime in the  60s or 70s is an interesting read, to start, or to get a historical perspective.