Repudiation: Accountability and Non-Repudiation Threats

Repudiation threats involve users denying their actions, making it impossible to prove what occurred. While often overlooked compared to more dramatic threats, repudiation can have serious consequences for regulatory compliance, fraud investigation, and dispute resolution. In systems handling financial transactions, healthcare records, or legal documents, non-repudiation is often a critical requirement.

Consider an e-commerce platform where users claim they didn't place orders, a healthcare system where staff deny accessing patient records, a financial system where traders disavow transactions, or a document management system where users deny approving documents. Without proper non-repudiation controls, organizations cannot prove what actually occurred, potentially leading to financial losses, compliance failures, or legal liabilities.

Technical repudiation might involve deleting or modifying log entries, spoofing IP addresses or user agents to obscure identity, exploiting weak authentication to claim account compromise, or manipulating timestamps to alter apparent sequences of events. Sophisticated attackers understand that covering their tracks through repudiation can be as valuable as the initial compromise.

Establishing non-repudiation requires comprehensive logging and auditing capabilities. Every security-relevant action must be logged with sufficient detail to reconstruct events. Logs must be protected against tampering through centralized collection, cryptographic signing, and immutable storage. Strong authentication ensures actions can be reliably attributed to specific users. Digital signatures on critical transactions provide cryptographic non-repudiation. Time synchronization across systems ensures accurate event correlation. Legal and regulatory requirements often dictate specific non-repudiation controls that must be implemented.