Which of the following is an example of a security measure that provides non-repudiation?

Non-repudiation refers to a security measure that ensures that a sender cannot deny having sent a message and that a recipient cannot deny having received it. Digital signatures fulfill this requirement by providing a unique, encrypted signature for a specific message or document that can be verified by other parties.

When a sender applies a digital signature to a message, it is generated using the sender's private key and can be decrypted and validated using the corresponding public key. This process not only verifies the authenticity of the message but also confirms that the message has not been altered in transit. Consequently, the sender cannot deny their intent to send the message, and the recipient can trust that the message truly comes from the claimed sender.

In contrast, while data encryption secures the contents of a message, it does not inherently provide proof of origin or integrity in the way that digital signatures do. SSL certificates are primarily used to secure communications over networks rather than specifically providing non-repudiation. Firewalls act as a barrier to control incoming and outgoing traffic but do not offer any mechanism for verifying the authenticity of specific communications or documents. Thus, digital signatures are the standout option when it comes to ensuring non-repudiation in digital communications.