Chain of Custody

The absolute assurance that an audit record has not been altered since its creation. This is achieved through cryptographic hashing, where any modification to the data—even a single bit—produces a completely different hash digest, immediately signaling corruption.

• Mechanism: Uses SHA-256 or BBS+ Signatures to generate a unique digital fingerprint.
• Implementation: Hash chains link sequential log entries, making retroactive alteration computationally infeasible.
• Verification: A Merkle Tree structure allows for efficient, partial verification of large datasets without rehashing the entire log.

The property that prevents an entity from denying its involvement in a logged action. It cryptographically binds an identity to a specific event, providing legal accountability for AI-driven decisions.

• Mechanism: A Digital Signature is created using the actor's private key, which can be universally verified with their public key.
• Infrastructure: Relies on a robust Public Key Infrastructure (PKI) or Decentralized Identifiers (DIDs) to manage and verify the trustworthiness of public keys.
• Token: A Non-Repudiation Token combines the signed log entry with a trusted timestamp to create a complete, undeniable proof of action.

The precise and verifiable sequencing of events to establish a definitive timeline. This is critical for reconstructing the causal chain of an AI system's decisions and proving what data was known at what time.

• Mechanism: A Timestamping Authority (TSA) issues a cryptographically signed timestamp that is embedded in the log entry.
• Structure: An Append-Only Log enforces strict chronological order, where new records can only be added to the end, preventing backdating or insertion.
• Anchoring: Blockchain Anchoring periodically publishes a hash of the log's current state to a public ledger, providing an independent, immutable proof of its existence at a specific point in time.

The hardware and software-enforced guarantee that once a record is finalized, it can never be overwritten, deleted, or modified. This creates a permanent, unalterable archive for long-term compliance.

• Storage: WORM Storage (Write Once, Read Many) provides a physical media-level guarantee of immutability.
• Architecture: Content-Addressable Storage (CAS) retrieves data by its hash, making any alteration result in a new, distinct address and preserving the original.
• External Proof: An Immutable Ledger or a Transparency Log like Sigstore provides a publicly auditable, append-only record of all log commitments, ensuring the system itself is operating correctly.

The ability for an independent third party to systematically validate the integrity, authenticity, and chronology of the entire chain of custody without needing to trust the system that created it.

• Proofs: Zero-Knowledge Proofs (ZKPs) allow for privacy-preserving verification, proving a log is compliant without revealing its sensitive contents.
• Completeness: A Proof of Retrievability (PoR) assures an auditor that the archived log is not only intact but can be fully recovered.
• Artifact Binding: A Model Inference Hash ties a specific AI prediction to its exact input, output, and model version, creating a verifiable AI Bill of Materials (AI BOM) for each decision.

The foundational security layer that protects the cryptographic keys used for signing and verification. Compromised keys destroy the entire chain of custody's credibility.

• Key Generation: A Hardware Security Module (HSM) generates and stores private keys in a tamper-resistant physical device, preventing extraction.
• Execution: A Trusted Execution Environment (TEE) or Confidential Computing enclave processes signing operations, protecting keys even from a compromised host operating system.
• Future-Proofing: Implementing Quantum-Safe Cryptography ensures that today's signed audit logs remain secure and non-repudiable against future attacks from cryptographically relevant quantum computers.