What constitutes "the most important papers" is highly subjective, so I will mention some of the papers that I think are influencial and that I have enjoyed reading.
I would start with this historical piece:
- Brassard, Gilles. "Brief history of quantum cryptography: A personal perspective." IEEE Information Theory Workshop on Theory and Practice in Information-Theoretic Security, 2005.. IEEE, 2005
Then, depending on your interests, there are several potential directions.
On quantum two-party crypto, some early papers had flawed (or incomplete) security proofs, but they are still a fun read.
- Brassard, Gilles, et al. "A quantum bit commitment scheme provably unbreakable by both parties." Proceedings of 1993 IEEE 34th Annual Foundations of Computer Science. IEEE, 1993.
- Bennett, Charles H., et al. "Practical quantum oblivious transfer." Annual international cryptology conference. Springer, Berlin, Heidelberg, 1991.
- Dominic Mayers. Unconditionally secure quantum bit commitment is impossible.
- Lo, Hoi-Kwong, and Hoi Fung Chau. "Why quantum bit commitment and ideal quantum coin tossing are impossible." Physica D: Nonlinear Phenomena 120.1-2 (1998): 177-187.
The bounded storage model is a nice assumption that can be used to overcome the impossibility.
- Ivan Damgård, Serge Fehr, Louis Salvail, and Christian Schaffner. Cryptography in the bounded-quantum-storage model.
On quantum key distribution protocols and proofs:
- The QKD protocols themselves are better learned through textbooks, e.g. Nielsen and Chuang's.
- Renato Renner's thesis introduced much of the theoretical foundation used to analyze QKD and other quantum cryptographic protocols.
On quantum money:
- Aaronson, Scott, and Paul Christiano. "Quantum money from hidden subspaces." Proceedings of the forty-fourth annual ACM symposium on Theory of computing. 2012.
- Zhandry, Mark. "Quantum lightning never strikes the same state twice. or: quantum money from cryptographic assumptions." Journal of Cryptology 34.1 (2021): 1-56.
I you want to see more recent work in quantum cryptography, some conferences to follow include:
- The IACR track of conferences (Crypto, Eurocrypt, TCC, etc.)
- QCrypt (specific to quantum crypto, theory + practice)
- To a lesser extent QIP and TQC, which are general quantum conferences.