What does a digital certificate NOT verify about a public key?

A digital certificate primarily serves to verify the ownership of a public key and the identity of the individual, organization, or entity that owns the key. In doing so, it helps establish trust in the public key, ensuring that it indeed belongs to a legitimate sender. The certificate itself is issued by a trusted third-party entity known as a Certificate Authority (CA).

The aspect that a digital certificate does not verify is whether the public key is encrypted. Public keys are, by their nature, designed to be widely accessible and are not encrypted, which allows anyone to use them to encrypt messages intended for the key's owner or to verify signatures made with the corresponding private key.

In contrast, verification of the sender's legitimacy, the connection's security status, and the validity of the certificate's signature are all within the purview of what a digital certificate ensures. This is vital for maintaining secure communications and ensuring that data integrity is upheld when using public key infrastructure (PKI).