Non-Repudiation Token

A cryptographic mechanism using asymmetric cryptography to prove the authenticity and integrity of a digital message. The signer uses a private key to create the signature, and any party with the corresponding public key can verify it. This binds an identity to the logged AI decision, providing the core non-repudiation property.

• Algorithm examples: ECDSA, EdDSA, RSA-PSS
• Key property: Only the holder of the private key could have generated the valid signature.

A cryptographic token issued by a Timestamping Authority (TSA) that proves specific data existed at a particular point in time. The TSA binds the hash of the AI audit record to a certified time source, creating a verifiable chronology.

• Standard: RFC 3161
• Function: Prevents backdating of logs and establishes a precise sequence of events for legal admissibility.

A sequential application of a cryptographic hash function where each link in the chain incorporates the hash of the previous record. This creates a tamper-evident structure: altering any single log entry would require recalculating all subsequent hashes, which is computationally infeasible.

• Common function: SHA-256
• Result: A verifiable, ordered sequence where the integrity of the entire chain depends on the integrity of every link.

The process of embedding a single Merkle root or aggregate hash of a batch of audit logs into a public blockchain transaction. This leverages the blockchain's global consensus and immutability to provide an independent, external witness to the existence and integrity of the records at that point in time.

• Benefit: Decouples the integrity proof from the organization's own infrastructure.
• Mechanism: The transaction timestamp and block hash serve as an irrefutable, public anchor.

The use of a Hardware Security Module (HSM) or Trusted Execution Environment (TEE) to generate and safeguard the private signing keys. The key material never leaves the secure hardware boundary in plaintext, ensuring the signing ceremony itself is non-repudiable and protected from host-level compromise.

• HSM: Dedicated physical device for key management and crypto-processing.
• TEE: A secure enclave within a main processor guaranteeing code and data confidentiality.

The application of post-quantum cryptography to ensure the non-repudiation of archived AI audit trails remains valid against future attacks by cryptographically relevant quantum computers. This involves replacing vulnerable algorithms like RSA and ECDSA with quantum-resistant alternatives.

• Threat: A future quantum computer could break current asymmetric cryptography, allowing an entity to repudiate a historically valid signature.
• Mitigation: Hybrid schemes combining classical and NIST-standardized post-quantum algorithms (e.g., CRYSTALS-Dilithium) for long-term archival integrity.

Establishes a cryptographic chain of custody for high-risk AI outputs, ensuring they meet evidentiary standards in court. A non-repudiation token binds the model version, input data hash, inference output, and operator identity into a single, verifiable package. This prevents an organization from plausibly denying that a specific model generated a specific, potentially harmful, decision. The token serves as a digital witness, proving that the log was not retroactively altered and that the decision originated from a known, authenticated system.

Enables real-time, auditable proof of regulatory adherence. Each non-repudiation token acts as a self-contained compliance artifact that can be streamed to a Verifiable Data Registry. Key benefits include:

• Continuous monitoring: Auditors can cryptographically verify compliance without accessing raw data.
• Automated filings: Tokens can be aggregated to generate tamper-proof reports for regulations like the EU AI Act.
• Selective disclosure: Using schemes like BBS+ Signatures, a token can prove a decision was reviewed by a human without revealing the human's identity.

In a Multi-Agent System, a single business process may involve a chain of delegated decisions. A non-repudiation token cryptographically seals each agent's action, creating an immutable provenance trail. This prevents a rogue or faulty agent from blaming another for a cascading failure. The token links each step via a hash chain, ensuring that the sequence of agentic decisions is tamper-evident and that each agent's liability is isolated and provable.

Creates a Model Inference Hash that acts as a non-repudiation token for a single prediction event. This token combines:

• The cryptographic hash of the input prompt.
• The generated output.
• The unique digest of the model weights (e.g., a SHA-256 of the safetensors file).
• A Timestamping Authority (TSA) counter-signature. This proves that a specific, unaltered model version produced a specific output at a specific time, which is essential for debugging model drift and contesting erroneous predictions.

To eliminate reliance on internal system integrity, the aggregate hash of a batch of non-repudiation tokens (a Merkle root) is periodically published to a public blockchain. This process, called blockchain anchoring, leverages the global consensus of a decentralized network to provide an irrefutable, external timestamp. Even if an organization's entire internal logging infrastructure is compromised, the anchored Merkle root proves that the audit trail existed in its exact state at that point in time, providing the highest level of non-repudiation.

Combines non-repudiation tokens with Zero-Knowledge Proofs (ZKPs) to satisfy auditors without exposing sensitive business logic or personal data. An organization can generate a ZKP that proves: 'A valid non-repudiation token exists, signed by an authorized Hardware Security Module (HSM), confirming a human-in-the-loop approved this high-risk decision.' The auditor verifies the cryptographic proof but learns nothing about the decision's data, the model's architecture, or the human operator's identity, preserving trade secrets and user privacy.