DittoBridge Contract

https://bscscan.com/address/0xdF11367EE135C8fb95b70769437FccB63D59092c

Implementation Notes

Our bridge contract DittoBridge is a secure EIP-712–based withdrawal bridge adapted from industry-standard OpenZeppelin components and inspired by designs such as Polygon FxPortal and Immutable X’s off-chain custody bridges. It enables seamless transfers between Ditto’s off-chain ledger and the on-chain DITTO token contract.

The bridge validates signed withdrawal permits issued by the backend using EIP-712 structured data signatures, ensuring tamper-resistant verification and replay protection. Deposits are emitted as on-chain events, allowing the backend to credit users’ off-chain balances.

The contract is implemented entirely with audited OpenZeppelin modules and does not introduce any new or unaudited logic beyond glue code connecting these modules.

Key Components

• OpenZeppelin security primitives: SafeERC20, ECDSA, EIP712, Ownable, ReentrancyGuard, Pausable.

  • Used to guarantee secure token handling, cryptographic signature validation, ownership control, and protection from reentrancy or paused states.
  • OpenZeppelin audit references:
    • https://docs.openzeppelin.com/contracts/5.x/api/token/erc20
    • https://docs.openzeppelin.com/contracts/5.x/api/utils#EIP712
    • https://docs.openzeppelin.com/contracts/5.x/utilities
    • https://docs.openzeppelin.com/contracts/4.x/api/security

• EIP-712 structured data signing:

  We use EIP-712 typed data to generate and verify backend-signed withdrawal permits.

  • EIP standard
    • https://eips.ethereum.org/EIPS/eip-712
  • Each (user, nonce) pair can be used only once, preventing replay or double withdrawals.

• Polygon FxPortal audit (inspiration):

  • Polygon’s FxPortal bridge uses the same message-verification model for withdrawals validated via signatures.
  • Audit reference
    • https://old.chainsecurity.com/wp-content/uploads/2022/12/ChainSecurity_Polygon_Fx_Portal_audit.pdf

• Immutable X / dYdX bridge inspiration:

  • Off-chain custody pattern where backend-signed slips authorize on-chain withdrawals.
  • Demonstrates mature production precedent for hybrid custody models.
  • Audit reference
    • https://www.dydx.xyz/blog/dydx-chain-audit

What We Changed vs Reference Designs (and Why)

1. Simplified architecture: We removed message-passing layers (e.g., child/parent state sync) and implemented a single-chain bridge focused on off-chain balance verification.
2. Added EIP-712 withdrawal slips: Our version explicitly binds each slip to (user, amount, nonce, expiry), with backend signer rotation for operational security.
3. Added deposit event tracking: Each user deposit emits a DepositCompleted event with a hashed external reference (e.g., Telegram ID) for the backend to process credits deterministically.
4. Vault controls:
   • ownerTopUpDitto() lets the admin replenish the vault.
   • ownerWithdrawDitto() enables rebalancing or draining of excess liquidity.
   • Both require owner authority and are non-reentrant.
5. Pausable safety: All external flows (deposit and withdraw) are guarded by whenNotPaused.