Public-key certificates, which are used to associate public keys with certificate owner identifiers, play an important role in public-key infrastructures. Each public-key certificate must be revoked as soon as its corresponding private key is compromised, lost or invalid. Before a public key is used, its associated public-key certificate must therefore be verified to ensure that it has not been revoked. However, the revocation and revocation notification of public keys are sometimes costly in terms of communication and computation requirements. A new unimplemented public-key encryption is proposed, which allows a user to update his private key without changing the corresponding public key, so that public-key revocation and revocation verification are not needed. In addition, the proposed scheme provides the following benefits: (1) prompt disabling of decryption capability (users' decryption ability can be revoked in real time); (2) personal key privacy (users select their partial private key without exposing it to certificate authorities) and (3) chosen-ciphertext security (the proposed scheme is provably secure against adaptive chosen-ciphertext attacks, in the random oracle model).

This work presents quantum key distribution protocols (QKDPs) to safeguard security in large networks, ushering in new directions in classical cryptography and quantum cryptography. Two three-party QKDPs, one with implicit user authentication and the other with explicit mutual authentication, are proposed to demonstrate the merits of the new combination, which include the following: 1) security against such attacks as man-in-the-middle, eavesdropping and replay; 2) efficiency is improved as the proposed protocols contain the fewest number of communication rounds among existing QKDPs; and 3) two parties can share and use a long-term secret (repeatedly). To prove the security of the proposed schemes, this work also presents a new primitive called the unbiased-chosen basis (UCB) assumption