Nonrepudiation uses a valid digital signature to provide evidence of the purported signer’s intent. If the private key remains secure and the signature scheme is unbroken, its owner cannot plausibly deny signing the data. section 9.2 section 9.7
A signature as evidence of intent
A signed digital contract, software package, or blockchain transaction can be checked with the signer’s public key. The verifier need not possess the private key, unlike a MAC verifier, so verification does not grant signing capability. section 9.2 section 9.7
Treat nonrepudiation as conditional engineering evidence:
- Protect the private key: a valid signature can be denied if an attacker obtained the key. section 9.2
- Use a sound signature scheme and implementation; forgery or key recovery invalidates the security claim. section 9.7
- Prefer asymmetric signatures when verifiers should validate evidence without sharing a signing secret. section 9.2 section 9.7
