Non-repudiation
Non-repudiation is the ability to prove that a specific action or transaction occurred and cannot later be denied by the parties involved.
“The degree to which actions or events can be proven to have taken place, so that the actions or events cannot be repudiated later.”
(Definition reproduced from the ISTQB Glossary. Copyright belongs to ISTQB.)
View the complete ISTQB GlossaryWhat is Non-repudiation?
Security mechanisms such as digital signatures, audit logs, and cryptographic techniques provide evidence of actions and identities.
Proof of origin: Demonstrates who performed an action.
Evidence preservation: Records remain trustworthy over time.
Security objective: Supports accountability and legal compliance.
Real World Example
A digital contract-signing platform lets customers sign loan agreements electronically. Six months later, a customer disputes ever having signed, claiming someone else must have done it.
The platform only stores "signed: yes," with no other evidence — there is no way to prove to a court or regulator that this specific customer, at this specific time, actually performed the signing action, so the dispute becomes unresolvable.
The tester verifies Non-repudiation directly: confirming the system captures a timestamped, cryptographically signed audit record tied to the authenticated user for every signing action, that the record can't be altered afterward without detection, and that the resulting evidence would actually hold up if challenged.
Testing finds that an admin can silently overwrite the audit log timestamp without leaving a trace — a serious Non-repudiation gap that would leave the company unable to prove the original signing event happened as claimed, exactly the property this concept exists to guarantee.
Practice Questions
Question 1
A customer disputes ever signing a digital loan agreement, and the platform can only show "signed: yes" with no other evidence. Which property has NOT been adequately verified?
Question 2
Which test check MOST directly verifies non-repudiation for an electronic signing feature?
Test your knowledge with real ISTQB-style questions
You’ve learned Non-repudiation. Test your understanding with topic-specific questions in our Mock Exams.