We are entering the era of the autonomous economy, where the volume of agent-to-agent (A2A) interactions is beginning to surpass human-to-machine interactions. AI agent decision-making has reached millisecond speeds, yet legal and financial liability for these decisions remains firmly with humans and organizations.
Core Challenges
Machine Speed vs. Human Responsibility: When an agent makes a mistake or exceeds its authority in a cross-company process (e.g., procurement or logistics), real-time auditing becomes impossible.
The Inter-corporate Trust Deficit: Traditional systems rely on database logs owned by one of the parties. These logs can be rewritten, deleted, or forged retroactively.
Inadequacy of Standard Logs: Typical text logs do not contain cryptographic proof that "this specific agent" had "this specific right" at "this specific point in time."
The Solution: Building an independent, neutral layer (Trust & Audit Layer) that decouples logic execution from action recording.
Threat Model: Specific Risks for AI Agents
To secure A2A interactions, we identify five critical attack vectors:
Impersonation: An attacker captures agent API keys or creates a clone to perform unauthorized transactions.
Agent Drift: Due to hallucinations or prompt errors, an AI agent begins performing actions outside its defined business role (e.g., placing a $1M order instead of $1K).
Replay Attacks: Intercepting a signed message and re-sending it to duplicate a payment or order.
Retroactive Log Tampering: Deleting compromising records from a centralized database after an incident is detected.
Multi-party Disputes: "Word-against-word" scenarios where Company A claims they didn't receive a request, and Company B cannot provably confirm it was sent.
Core Primitives: The Technological Foundation
The system is built on five cryptographic pillars:
DID + Keys (Identity): Every agent possesses a Decentralized Identifier (DID). Public keys are stored in a registry; private keys are held in the agent's secure HSM/KMS.
VC/Attestations (Authority): Verifiable Credentials define the agent's scope, limits, expiry, and revocation conditions. Credentials are verified cryptographically before every action.
Signed Envelopes: Every message between agents is wrapped in a signed envelope containing a nonce (replay protection) and TTL (time-to-live).
Signed Receipts: Upon execution, the agent (or receiving party) generates a receipt—a legally significant confirmation of the transaction.
Merkle Batching + On-chain Anchoring: Receipts are aggregated into a Merkle tree. The root is regularly written to a public blockchain as an "immutability anchor." This allows for proof of receipt validity without disclosing content on-chain (privacy-preserving audit).
Architecture and Integration
Stack Placement
The system is implemented as a Trust Proxy or Sidecar SDK positioned in the agent's traffic path. Integration includes support for A2A protocols and Model Context Protocol (MCP) tools.
Data Storage
Off-chain: Full receipt and VC data are stored in local organizational storage or an encrypted cloud service.
On-chain: Only 32-byte hashes (commitments) reach the blockchain, ensuring extreme cost-efficiency and scalability.
Audit Console
A specialized interface for security officers and compliance managers:
Search by agent ID or transaction ID.
Cryptographic proof verification.
Exportable reports for regulators.
MVP, Implementation, and Metrics
Phases of Deployment
Shadow Mode: The system records agent actions and validates them against policies (VC) without blocking traffic, building an analysis baseline.
Enforcement Mode: The system proactively blocks actions that are unsigned or violate policy constraints.
Efficiency Metrics
Time-to-investigate (TTI): Reducing incident investigation time from days to minutes.
Policy Violations Count: Number of prevented unauthorized actions.
Coverage %: Percentage of business processes protected by the trust layer.
Cost per 1k Receipts: Target cost of less than $0.01 per 1,000 recorded actions.
Future Roadmap
Developing a Cross-org Trust Graph and implementing Consortium Governance mechanisms for automated dispute resolution without legal intervention.