Which of the following describes the digital signature of a Certificate Authority (CA)?

The digital signature of a Certificate Authority (CA) is fundamentally a technique to sign digital documents, which serves to ensure their authenticity and integrity. When the CA issues a digital certificate, it uses its private key to create this signature on the certificate. This signature can then be verified by anyone using the corresponding public key of the CA, assuring users that the certificate has not been tampered with and that it indeed comes from a trusted source.

This process of signing is crucial to the functioning of Public Key Infrastructure (PKI) because it establishes trust in the digital certificates that facilitate secure communications and transactions. In essence, the digital signature validates the identities of entities exchanging information over insecure channels, ensuring that digital documents have not been altered in transit and confirming the legitimacy of the signatory.

In contrast, other options presented do not accurately reflect the role of a digital signature in this context. Encrypting data is not the primary purpose of a digital signature; it is aimed at confirming authenticity. Labeling the digital signature as irrelevant undermines its critical importance in certificate management. Lastly, while public keys play a significant role in user authentication, a public key itself does not function as a signature; it is the private key that is used to create the signature.