Cross-Chain, Mixers, and Privacy-Enhancing Technologies
This domain tests how value moves between chains and how privacy tools change traceability. You need to explain what each tool hides and what metadata remains.
Bridges and wrapped assets
Lock-and-mint bridges lock an asset on the source chain and mint a representation on the destination chain. Trace the lock transaction, the bridge contract, the mint event on the destination chain, and any later redemption. Third-party bridges add a custodian or validator set, which is a separate attribution target.
Mixers and CoinJoin
- Tornado Cash uses fixed-denomination pools (0.1, 1, 10, 100 ETH) and withdrawals to fresh addresses, optionally via a relayer. Deposits and withdrawals are visible, but linking a specific deposit to a specific withdrawal requires off-chain data or timing correlation.
- CoinJoin combines inputs from multiple users into equal outputs, breaking simple common-input ownership.
Privacy coins
Monero uses ring signatures (current ring size 16), stealth addresses and RingCT to hide sender, receiver and amount. View keys can support lawful disclosure.
Worked example
10 ETH enters a Tornado 10-ETH pool at 12:00 and two 10-ETH withdrawals leave at 14:00 and 19:00. Reasoning: the pool balance shows three 10-ETH deposits and two withdrawals in the window; you cannot state which deposit funded which withdrawal from chain data alone. You can report timing and pool-level flows, and seek relayer or exchange records to link a withdrawal to an off-ramp.
Traps
- Claiming a mixer breaks the trail completely.
- Matching deposits to withdrawals by amount alone.
- Ignoring bridge mint events on the destination chain.
- Assuming privacy-coin tracing is impossible; it often relies on exchange and view-key data.