What action does nonrepudiation help ensure in online transactions?

Nonrepudiation is a critical concept in online transactions, ensuring that parties involved in a transaction cannot deny their involvement or the authenticity of the transaction. This is typically achieved through the use of cryptographic techniques such as digital signatures. By providing a way to verify the origin and integrity of electronic messages or transactions, nonrepudiation helps in avoiding disputes that may arise over whether a transaction occurred as claimed.

When a transaction is sealed with a digital signature, for instance, the sender cannot deny having sent the message, as the signature ties them to the transaction. This not only builds trust between parties but also provides legal evidence, should a dispute arise. Therefore, ensuring that both parties are held accountable for their actions in a transaction reinforces the trust necessary for conducting business online. The other options do not capture this accountability feature that is central to nonrepudiation in online transactions.