Safe Signing

Threat Model

DeFi signing threat analysis: clipboard hijacking, blind signing, extension compromise, memory scraping, TX substitution, and approval farming. Why private keys must never exist on networked machines.

Hot machine threats What Safe Signing protects Limitations

Simulation proves a transaction is safe to execute. But safe calldata is worthless if the signing environment is compromised. This page covers the threats; the Signing Flow shows how x0x1 defends against each one.

Why signing on a hot machine is dangerous

A "hot machine" is any computer connected to the internet. This includes your desktop, your phone, and most laptops. The threat surface is enormous:

Clipboard hijacking

Malware replaces copied addresses. Funds sent to attacker.

Blind signing

Wallet shows hex blob, user clicks "confirm". Arbitrary contract calls executed.

Extension compromise

Malicious MetaMask update leads to key extraction or TX substitution.

Memory scraping

Malware reads decrypted keys from RAM. Full wallet compromise.

TX substitution

Man-in-the-middle between dApp and wallet. Different TX gets signed.

Approval farming

Infinite token approvals left active. Delayed drain at attacker's convenience.

What Safe Signing protects against

Keys and internet never coexist on the same device. Physical separation, not software isolation:

No private key ever touches a networked machine. This is not a software guarantee — it's a physical architecture constraint. The signing device is air-gapped.

What Safe Signing does NOT protect against

Smart contract bugs in the target protocol (mitigated by Anvil simulation + risk checks)
Social engineering of the user (mitigated by state diff review)
Physical compromise of the signing device (mitigated by hardware wallet integration)
Compromised RPC provider returning false state. Anvil fork catches execution-level lies. Multi-RPC cross-check is planned but not yet implemented.

Now that you know the threats, see exactly how the Signing Flow implements physical device separation with a three-device architecture.