Cybersecurity computer infrastructure representing smart contract signatures and permission checks

An AI agent that prepares token transactions can save users several clicks, but gasless approval signatures should not become invisible spending authority. This technical runbook compares ERC-2612 permit fields with EIP-712 signing domains and proposes a reproducible set of wallet approval tests.

What a permit authorizes, and what it does not

ERC-2612 defines a signed permit that updates the ERC-20 allowance for a specific spender, value and nonce before a deadline. The signer can authorize that allowance without first submitting a standalone on-chain approval transaction. The signature is not itself proof that a subsequent trade is profitable, safe or even intended by the user. An AI agent should distinguish the proposed swap from the separate authorization to let a contract transfer tokens. Otherwise a conversational instruction such as ‘compare the cheapest routes’ can be mistakenly interpreted as consent to an allowance. The original ERC-2612 proposal was created in April 2020, and it should be read as a narrow token interface extension rather than a blanket autonomous-agent standard. Each token integration needs contract-level testing because implementations and signature conventions can differ from common examples.

Bind every approval to a visible spender and value

The permission screen should show the token contract, chain ID, spender address, approval amount, proposed operation and deadline as independent reviewable fields. A friendly protocol name can accompany an address but must never replace it. The user should see whether the amount is exact, a modest bounded maximum or an unlimited allowance. For an example design, approving 100 units for a planned 40-unit swap leaves a residual authority that may outlast the transaction. The interface should explicitly explain this difference instead of promising that approvals are consumed automatically. A smart agent should default to a just-enough value when the transaction route is stable and provide a documented exception path for repeated interactions. Never silently upgrade a fixed limit to a maximum integer because an integration library makes that convenient.

Use the EIP-712 domain as a security boundary

EIP-712 describes structured typed-data signing, including domain parameters such as name, version, chainId and verifyingContract. It explicitly notes that the standard does not itself supply replay protection. ERC-2612 adds nonce and deadline conditions for its permit semantics, and the token implementation uses a domain separator to prevent accidental cross-domain reuse. For an agent wallet, the displayed domain must match the actual verifying contract and current chain context. Developers should reject mismatches rather than auto-correct a signature after a network switch. A signature copied from one token should fail when replayed against an unrelated token. Test signatures from a stale domain version, an expired deadline, an altered spender address and a nonce already consumed. These are specification-driven checks, not a claim that every wallet interface enforces them identically.

Model frontend phishing and the relayer threat

The party submitting a permit need not be the token owner. ERC-2612 notes that any caller can relay a valid signature, which means an agent cannot rely on the transaction sender as the original authorizer. A relayer may submit the signature earlier than expected or withhold it until a convenient time before expiry. The product must not treat a signed permit as though it has already executed. Track prepared, signed, submitted, confirmed, expired and rejected as distinct states, and query the actual allowance and nonce after confirmation. A fraudulent interface might ask the user to approve a well-known token but point to a malicious spender. Address verification, contract provenance and narrowly scoped consent must therefore remain accessible before the signature prompt. Never request private keys or seed phrases as a shortcut to approval automation.

A six-case test matrix for AI-assisted transaction flows

Build an isolated test environment with a real ERC-2612-compatible token contract and a controlled spender. First test an exact-value permit that is used once. Second, replay the same signature after the nonce changes. Third, alter one byte of the spender address and assert signature rejection. Fourth, switch networks so chain IDs differ. Fifth, let the deadline expire and verify the transaction reverts. Sixth, submit a valid permit through a different relayer and confirm that the end-state allowance is the same as the authorization, not an agent-generated guess. Capture contract calls, signed structured data, UI screenshots and expected-versus-observed allowance values. These are proposed tests; they should not be presented as measured attack statistics. Re-run the matrix whenever token adapters or wallet libraries change.

Ship an agent authorization ledger, not invisible automation

A useful permission ledger stores a hash of the typed message, token and spender identifiers, intended business action, user confirmation time and on-chain transaction reference. Keep the full signature only for as long as operationally required and avoid displaying sensitive authorization artifacts in public logs. If an agent prepares multiple alternatives, each route change should trigger a fresh risk review rather than inheriting a broad grant from the first candidate. Present a clear cancellation path while the permit has not been submitted, and explain that on-chain approvals require a separate revocation or replacement transaction once executed. The product’s success metric is not the number of frictionless signatures. It is the proportion of transactions where the user can accurately predict the authority granted, observe the resulting allowance and reverse residual risk when needed.

Sources

Editorial photograph: Michael Förtsch / Unsplash.