The most regularly performed nontrivial task using quantum information to date has been quantum key distribution. Quantum key distribution (QKD) is a method of securely distributing cryptographic key material for subsequent cryptographic use. In particular, it is the sharing of random classical bit strings using quantum states. Its use of a set of nonorthogonal quantum states then requires this key material to be considered quantum information.1 The quantum encoding of cryptographic keys for distribution is valuable because the no-cloning theorem and the superposition principle governing quantum states confer a uniquely powerful form of information security during transmission of key bits. For maximal security, it can be followed by one-time pad message encryption, which is the only cryptographic method that has been proven to be unbreakable once a random key has been securely shared.
KeywordsQuantum Channel BB84 Protocol Plaintext Message Unambiguous State Discrimination Eavesdrop Strategy
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