Public-Key Authority utilises Publicly Available Directory# but tighten the control over #public key distribution. Before the user could talk to the other user, they are required to obtain public key by interacting with the directory in real-time when needed. And the user must know the public key of the directory in order to be able to interact with it.
Public-Key Authority
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Public-Key Certificate
Public-Key Certificate is issued or signed by a trusted public-key or Certificate Authority (CA) which binds identity to public key. It allows #public key exchange without real-time access to Public-Key Authority. The certificate can be verified by anyone who knows the public-key authority’s public key.
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Asymmetric Cryptography
It addresses two issues faced by Symmetric Cryptography: Key Distribution# and Digital Signature#. One doesn’t need to have a secure channel or a third party to distribute public keys as it will not sufficient to undermine the security of the encrypted message. Public keys could be distributed by either Public Announcement#, Publicly Available Directory#, Public-Key Authority#, or Public-Key Certificate#. We can verify whether the message is coming from the intended sender using the public key, thus able to authenticate the author. That being said, it is vulnerable to quantum computing.