Public Key Infrastructure (PKI)
by Froga
Learn how trust is built on the internet. Explore how public–private key pairs, digital certificates, and Certificate Authorities work together to authenticate identities, secure communication, and prevent tampering.
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Study material
A digital certificate connects an identity claim, such as a host name, with a cryptographic verification key. A client must check that the identity in the certificate matches the identity it intended to reach; a valid signature alone is not enough. It also checks that the certificate is within its allowed time and that its signing chain leads to a trusted authority.
A client connects to service.example.net, but the server presents a certificate issued only for billing.example.net. What should a correctly validating client do?
multiple choice
Accept the connection because hostname checking is only needed for email
Accept the connection because any certificate signed by a CA is valid for every host
Use the certificate to ask the CA for the server's private key
Reject the connection because the certificate does not authenticate the requested host
The certificate must identify the same host the client intended to contact.
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