Final answer:
Nonrepudiation is a concept in cryptography that ensures a person cannot deny the validity of their digital actions, often enforced through digital signatures.
Step-by-step explanation:
Cryptography is employed to protect information and establish trust in the digital world. One aspect of this is ensuring that once a person has sent a message or committed to a transaction, they cannot deny having done so later. The ability to prove that an action occurred and prevent denial of this action is known as nonrepudiation. Nonrepudiation is crucial in digital communications and transactions because it ensures that once individuals make a commitment, such as sending an email or signing a digital document, they cannot later claim that they did not. This is often enforced through the use of digital signatures and certificates that uniquely tie actions to individuals.