Why autonomous AI agents need a tamper-evident black box

Autonomous AI agents are starting to act without a human in the loop: rebalancing a treasury, approving a payout, triaging a support queue, routing a payment. The moment an agent acts on its own, a hard question appears � after something goes wrong, how do you prove what the agent actually decided, in what order, and that the record was not edited afterward? A log file the operator can rewrite is not evidence. Screenshots are not evidence. The phrase trust me, the model said so is the opposite of an audit trail.

Aviation solved the analogous problem with the flight recorder: a tamper-resistant device that captures every input and action continuously, so investigators can reconstruct exactly what happened without trusting any single party. AI agents need the same thing � a black box. The mechanism is straightforward: each decision record (the input hash, the output, the model id, a timestamp) is signed, and each entry is chained to the hash of the previous one. Sign one byte differently, or remove an entry, and the chain no longer verifies. An auditor, an insurer, or a regulator can later demand the full signed history and check it independently � no trust in the operator required.

Using post-quantum signatures (Dilithium-2, NIST FIPS 204) matters here because these records must stay verifiable for years; a log signed with classical ECDSA becomes forgeable once large quantum computers arrive. Be honest about scope, though: a black box proves authenticity, ordering, and integrity of what was logged � it does NOT prove the agent reasoned correctly, and it cannot prove that nothing was omitted before an entry was ever written. Saying that plainly is the point: it is resistant to known classical and quantum attacks per NIST, and no signature scheme is secure forever. It is an accountability layer, not a correctness oracle. For anyone deploying agents that move money or make consequential decisions, that accountability layer is quickly becoming non-optional.