Digital signatures provide a way to ensure non-repudiation as they are unique to each user and cannot be replicated by others. They use a mathematical scheme for demonstrating the authenticity of a digital message or document. When a document is signed digitally, it is nearly impossible for the signer to deny having signed it. As for the other options: Salting is used in conjunction with hashing to protect passwords, and while a multi-factor authentication enhances the security of a system, it doesn't concern non-repudiation. Hash values, while unique to the content they represent, do not by themselves provide non-repudiation, as they do not bind a document or message to a specific individual's identity.