Cross-Chain NFT Bridge: How to Ensure Consistency and Prevent Duplicate Minting?

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I am developing a multi-chain NFT bridge that facilitates transfers across three blockchain networks:

:one: Private Ethereum Network (Chain 1) – Our primary ecosystem.
:two: Ethereum Mainnet (Chain 2).
:three: Polygon (Chain 3).

:link: NFT Bridging Process

  1. Users select an NFT on the private chain and initiate the bridging process.
  2. The NFT is locked on the private chain.
  3. Once locked, a "Claim" button appears, allowing users to mint the NFT on a destination chain.
  4. The bridge admin verifies the lock and provides a signature & NFT metadata for minting on the selected destination chain.
  5. The user initiates the transaction via MetaMask to complete the minting process.

:warning: Security Concern

  • A user can attempt to claim on Ethereum, receive a valid signature, but reject the transaction.
  • They can then repeat the process on Polygon, obtaining a second valid signature.
  • With both signatures, they could mint the NFT on both chains, leading to duplication issues.

:hammer_and_wrench: Challenges & Constraints

  • We explored timestamp-based validity, but it might give high failure rates? due to timestamp validations.
  • The bridge admin does not cover minting costs, meaning users must pay gas fees themselves.

:red_question_mark: How can we ensure cross-chain consistency and prevent duplicate minting while maintaining decentralization and avoiding unnecessary admin costs?

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