x402

Payment Proof & Signatures

x402 Track 03
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How to Create Unforgeable Payment Proofs

EIP-712 signatures are mathematically tamper-proof.
They simultaneously prove who signed and what was signed.

What you'll learn

  • β†’The 4-layer structure of EIP-712 signatures (domain, type, message, signature)
  • β†’Why amount/recipient tampering and replay attacks are impossible
  • β†’How Permit (EIP-2612) grants payment allowance without user gas
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Typed Signing

Signing a typed structure rather than a raw message makes the intent explicit.

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Domain Separation

Locks signatures to a specific app, chain, and contract to prevent cross-app reuse.

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Permit

Grants ERC-20 allowance with a single signature. Zero gas for the user.