Publicly Available Directory is a public storage for #public key retrieval where participants could register keys in it. It must contain entries in the form of name with associated public keys, periodically published and able to be accessed electronically. The participants should register securely with the directory and able to change their keys at any time. However, like Public Announcement, it is still vulnerable to forgery.
Publicly Available Directory
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Public-Key Authority
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.
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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.