Skip to content
Software Architecture Guide

Nonrepudiation

Explanation

Section titled “Explanation”

Nonrepudiation is a sub-characteristic of security in the ISO/IEC 25010 quality model (see the article ISO/IEC 25010 Product Quality Model). The standard describes it as the degree to which actions or events can be proven to have taken place.

In practice, an author cannot successfully dispute that they wrote a statement. They also cannot dispute the validity of a contract tied to it.

Related properties. Two sibling sub-characteristics support it:

  • Accountability means tracing actions uniquely to one entity.
  • Authenticity means proving that an identity is the one claimed. Without it, you cannot attribute an action to anyone.

Digital signatures. A digital signature gives non-repudiation that anyone can verify. A message authentication code (MAC) is different. It relies on a shared secret, so it cannot offer the same public proof.

Certificates. A public key certificate lets anyone check a signature. Certificate authorities attest to whom a certificate belongs.

Trusted third parties. A trusted third party is an independent party that all sides rely on. Involving one is the standard way to reduce the risk that signers disown their signatures. A time stamping authority is one kind. It issues tokens showing that data existed at a given point in time.

Example

Section titled “Example”

An online shop receives an order from a customer. The customer signs the order with a private key. The shop checks the signature using the customer’s public key certificate. A time stamping authority adds a token showing when the order existed. Later, the customer claims they never placed the order. The shop shows the signed, time-stamped order as proof.

Trade-offs

Section titled “Trade-offs”

Key management is the main weakness. If a signing key is not properly safeguarded, someone can forge signatures. That undermines non-repudiation. Teams that rely on signatures must therefore protect keys carefully.

Checks

Section titled “Checks”
  • The document states which actions must be provable and how, for example with digital signatures.
  • Signing keys are protected, and the document says how, because forged signatures would undermine non-repudiation.
  • The document names a trusted third party, such as a certificate authority or time stamping authority, where proof must hold up against disputes.
Section titled “Related”

Sources

Section titled “Sources”