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signature-replay

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Signature replay attacks — missing nonces, missing chain ID, ecrecover zero address, signature malleability, cross-chain replay.

packages/decepticon/decepticon/skills/standard/contracts/signature-replay/SKILL.md

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Nov 9, 2026
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Apache-2.0

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# Signature Replay Playbook

EIP-712 signatures, permits, meta-transactions, and cross-chain bridges
all use `ecrecover` (or its variants). Each has well-known bugs.

## Bug classes

### 1. Missing nonce → replay
```solidity
function execute(uint256 amount, bytes calldata sig) external {
    bytes32 h = keccak256(abi.encodePacked(msg.sender, amount));
    address signer = ecrecover(h, ...);
    require(signer == owner);
    // ... withdraw amount
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