NonRepudiation is a Key Usage bit that is asserted when the Certificate Subject Public Key is used to verify Digital Signature, other than signatures on certificates (bit 5) and CRLs (bit 6), used to provide a Non-Repudiation service that protects against the signing entity falsely denying some action.

NonRepudiation in the case of later conflict, a reliable Third-party may determine the authenticity of the signed data. (Note that recent editions of X.509 have renamed the NonRepudiation bit to contentCommitment.)

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