However, traditional PKI systems have significant limitations:

• Administrative trust dependencies: Reliance on CAs as trusted third parties
• Key rotation vulnerabilities: Rotating keys breaks the chain of trust
• Centralized points of failure: CA compromise affects all downstream certificates
• Portability limitations: Identifiers are locked to specific trust domains

KERI's Approach

KERI fundamentally reimagines non-repudiation by replacing administrative trust with cryptographic root-of-trust through self-certifying identifiers (SCIDs).

Self-Certifying Identifiers

In KERI, non-repudiable signatures are created using private keys associated with Autonomic Identifiers (AIDs). The verification process allows anyone to:

1. Extract the public key directly from the identifier itself or from incepting information uniquely associated with the cryptographic derivation process
2. Verify signatures without relying on external certificate authorities
3. Establish control authority through the Key Event Log (KEL)

This creates a self-contained mapping between an identifier and its controlling public key embedded within the identifier structure itself, eliminating dependency on trusted third parties.

Security Overlay Architecture

KERI functions as an identifier-system security overlay for IP packets, establishing message authenticity through:

• Cryptonymous AIDs: Messages are verifiably attributed to self-certifying identifiers
• Asymmetric keypair signatures: One or more non-repudiable digital signatures are attached to messages
• Key Event Logs: Verifiable data structures prove the current valid set of asymmetric keypairs

Message Authentication Process

An authenticatable (verifiable) internet message or data item in KERI includes:

• The identifier in the payload
• The data in the payload
• Attached digital signature(s) made with private key(s) from controlling keypair(s)

Verification workflow:

1. Verifier receives message with identifier in payload
2. Verifier uses identifier system mapping to look up public key(s) from controlling keypair(s)
3. Verifier checks attached signature(s) using the public key(s)
4. Because the payload includes both identifier and data, the signature creates a non-repudiable cryptographic commitment to both the source identifier (who) and the message data (what)

Pre-Rotation and Post-Quantum Security

KERI's pre-rotation mechanism provides additional non-repudiation guarantees:

• Forward commitments: Each key event includes cryptographic digests of next keys
• One-time use: Rotation keys are used exactly once, minimizing exposure
• Post-quantum protection: Hidden pre-rotated keys resist future quantum attacks
• Recovery capability: Compromise of current keys doesn't compromise pre-rotated keys

This ensures that even if current signing keys are compromised, the non-repudiable commitments made with pre-rotated keys remain secure.

Duplicity Detection

KERI's duplicity detection mechanisms enhance non-repudiation by making controller misbehavior evident:

• Internal consistency: Prevented by log verification from self-certifying root-of-trust
• External inconsistency: Detected when multiple verifiable but conflicting logs exist
• First-seen policy: Ensures "first seen, on the record, always wins"
• Ambient verifiability: Anyone can verify anywhere, at any time

If a controller signs two conflicting events, both signatures serve as cryptographic proof of duplicitous behavior, making repudiation impossible.

Practical Implications

Use Cases

Non-repudiation in KERI enables critical applications:

Legal Entity Verification: The vLEI (verifiable Legal Entity Identifier) system uses KERI's non-repudiation to create cryptographically verifiable organizational credentials. When a Legal Entity Official Organizational Role holder signs a document, the signature provides non-repudiable proof of authorization.

Supply Chain Provenance: ACDCs (Authentic Chained Data Containers) use non-repudiable signatures to create verifiable chains of custody. Each transformation or transfer in a supply chain is signed, creating an immutable audit trail.

Credential Issuance: When a Qualified vLEI Issuer (QVI) issues credentials, the issuance event is signed with non-repudiable signatures anchored to the issuer's KEL. The issuer cannot later deny having issued the credential.

Regulatory Reporting: Organizations can submit regulatory reports with non-repudiable signatures, providing cryptographic proof of submission that satisfies compliance requirements without requiring trusted intermediaries.

Benefits

Decentralized Trust: Non-repudiation without certificate authorities eliminates single points of failure and reduces infrastructure dependencies.

Portability: Identifiers and their non-repudiation properties are portable across trust domains, enabling cross-organizational workflows.

Scalability: Each identifier has its own KEL, avoiding global consensus bottlenecks while maintaining non-repudiation guarantees.

Legal Defensibility: Cryptographic proofs provide objective evidence in disputes, with mathematical certainty rather than procedural trust.

Privacy Preservation: Non-repudiation can be achieved with cryptonymous identifiers, separating authentication from identification.

Trade-offs

Key Management Responsibility: Controllers bear full responsibility for protecting private keys. Key compromise undermines non-repudiation, though KERI's pre-rotation provides recovery mechanisms.

Computational Overhead: Signature generation and verification require cryptographic operations, though modern hardware makes this negligible for most applications.

Complexity: Understanding and implementing KERI's non-repudiation mechanisms requires cryptographic expertise, though libraries and tools abstract much of this complexity.

Irrevocability: Non-repudiable commitments cannot be undone. While KERI supports key rotation and credential revocation, the historical record of signed events remains immutable.

Security Properties

KERI's non-repudiation achieves SUF-CMA (Strong UnForgeability under Chosen Message Attack) properties through Ed25519 signatures, providing:

• Existential unforgeability: Attackers cannot forge signatures even after seeing many valid signatures
• Strong unforgeability: Even the signer cannot create two different valid signatures for the same message
• Key substitution resistance: Attackers cannot substitute their own public key for the legitimate one

These properties ensure that non-repudiation guarantees hold even against sophisticated adversaries with significant computational resources.

Legal Considerations

When implementing non-repudiation for legal purposes:

• Ensure compliance with electronic signature regulations (eIDAS, ESIGN, etc.)
• Maintain audit trails of signature operations
• Implement timestamp services for temporal proof
• Document key management procedures and policies
• Establish dispute resolution processes for signature challenges