The classification of quantum symmetric-key encryption protocol is presented. According to five elements of a
quantum symmetric-key encryption protocol: plaintext, ciphertext, key, encryption algorithm and decryption
algorithm, there are 32 different kinds of them. Among them, 5 kinds of protocols have already been constructed
and studied, and 21 kinds of them are proved to be impossible to construct, the last 6 kinds of them are not
yet presented effectively. That means the research on quantum symmetric-key encryption protocol only needs to
consider with 5 kinds of them nowadays.
We investigate the definition of security for encryption scheme in quantum context. We systematically define the
indistinguishability and semantic security for quantum public-key and private-key encryption schemes, and for
computational security, physical security and information-theoretic security. Based on our definition, we present a
necessary and sufficient condition that leads to information-theoretic indistinguishability for quantum encryption
scheme. The equivalence between the indistinguishability and semantic security of quantum encryption scheme
is also proved.
Ekert91 protocol of quantum key distribution is an important protocol of key distribution that based on the quantum mechanics. According to it, we first discuss the variance functions of Bell inequality test and error rate comparison, and then define the sensitivities of two security strategies based on Bell inequality test and error rate comparison respectively. Finally we give out the eavesdropper's optimal attack strategy and compare the sensitivities of two security strategies.