Describe the public key infrastructures.

What will be an ideal response?

Public key infrastructures (PKIs) evolved to facilitate asymmetric transactions. The term PKI describes the collection of technologies, protocols, and policies that maintain, distribute, create, and validate public keys and their associated information. PKIs serve as the trusted third party in a secure transaction and involve a certificate authority (CA), a key directory, and all of the associated management rules. Other components such as key recovery, and registration procedures, may also be included in a PKI.

The function of a PKI is to provide a digital certification through a CA, which is then verifiable through a Registration Authority (RA). A digital certificate is a public document that contains information which identifies a user, the user's public key, the time during which the certificate is valid, and other information. The digital certificate is unique to the individual user.