ShadowBid

What is ShadowBid?

ShadowBid is a confidential sealed-bid auction protocol built on Arbitrum Sepolia, powered by iExec Nox. It solves a fundamental problem with on-chain auctions: every bid is public. In a standard on-chain auction, anyone watching the chain can see your bid amount and outbid you by the smallest possible increment. Sealed-bid auctions are supposed to prevent this but until now, they couldn't be enforced on a public blockchain.

ShadowBid enforces sealed bids cryptographically using a commit-reveal scheme, and integrates iExec Nox Confidential Tokens at settlement so the winning payment amount is wrapped into a confidential asset never exposed as plaintext on the public ledger.

How it works

Bid phase: Bidders generate a commitment hash off-chain: keccak256(amount, salt, address). They submit the hash and deposit USDC to the vault. Nobody not even the auctioneer can see the bid amount.

Reveal phase: After the bid deadline, bidders reveal their (amount, salt) pair. The contract verifies the hash matches. Invalid reveals are rejected. The highest valid reveal becomes the winner.

Settlement: The vault calls IConfidentialWrapper.wrap()the winning USDC amount is wrapped into an iExec Nox Confidential Token and sent to the auctioneer. The settlement amount is hidden from the public chain. Losing bidders receive full USDC refunds instantly.

iExec Nox integration

At settlement, ShadowBidVault.settleAuction() calls the Nox Confidential Wrapper:

USDC.approve(address(C_WRAPPER), winningAmount); C_WRAPPER.wrap(auctioneer, winningAmount);

The auctioneer receives a confidential token, the winning bid amount is hidden from block explorers and on-chain observers. This is the core Nox integration: the winning payment becomes a private, auditable, TEE-shielded asset.

Why sealed-bid auctions matter

Sealed-bid auctions are used for government procurement, spectrum licensing, real estate, and financial instruments — precisely because public bidding creates unfair advantages. ShadowBid brings this mechanism on-chain for the first time with cryptographic enforcement and confidential settlement via iExec Nox.