What does it mean for a digital signature to be described as "non-repudiable"?

A digital signature being described as "non-repudiable" means that the signer cannot deny having signed a digital document or message. This characteristic is a fundamental aspect of digital signatures and ensures the integrity and authenticity of electronic communications. When a digital signature is created, it is uniquely linked to the signer’s identity through a cryptographic process, typically involving the signer’s private key. This linkage establishes a strong evidence trail that supports the originating party's claims about the document’s authorship. Thus, if a dispute arises regarding the signed document, the signer is unable to refute their involvement, providing legal standing and trust in transactions.

The other options do not align with the definition of non-repudiation. For example, digital signatures are designed to not be easily altered, and they do not require multiple signatures for validity unless specified by a particular process or framework. Additionally, non-repudiable signatures do not have inherent time limitations as their validity is determined by the cryptographic keys involved rather than by a temporal condition.