Non-repudiation is the concept of ensuring that a contract, especially one agreed to via the Internet, cannot later be denied by one of the parties involved. In today's global economy, where face-to-face agreements are often not possible, non-repudiation is becoming extremely important to commerce.

With regards to digital security, non-repudiation means that it can be verified that the sender and the recipient were, in fact, the parties who claimed to send or receive the message, respectively. In other words, non-repudiation of origin proves that data has been sent, and non-repudiation of delivery proves it has been received.

Traditional methods such as seals or signatures are vulnerable to forgery. Digital transactions are also potentially subject to fraud, such as when computer systems are broken in to or infected with trojan horses or viruses. Participants can potentially claim such fraud to attempt to repudiate a transaction.