Which of the following illustrates the concept of non-repudiation in digital communication?

The concept of non-repudiation in digital communication is primarily concerned with ensuring that a sender cannot deny having sent a message. This is crucial for legal and contractual communications, where one party must be held accountable for their actions. When a sender uses mechanisms such as digital signatures, they create a unique signature that ties them to the message in such a way that they cannot argue against sending it later. This level of accountability helps establish trust in digital communications.

In contrast, while verifying content, encrypting messages, and changing hash values are important aspects of digital communication, they do not directly address the issue of a sender’s denial regarding their involvement. Content verification ensures that the recipient confirms they received the correct information, encryption protects the message confidentiality, and hash values serve to verify integrity and authenticity, but none of these elements provide evidence that the sender sent the message in the first place. Therefore, only the option highlighting the sender's inability to deny sending the message directly illustrates non-repudiation.