How do non-custodial swap services settle trades without holding your funds
Non-custodial swap services settle trades by using smart contracts or atomic swaps that execute the exchange only when both parties have met their obligations. Your funds never enter a wallet controlled by the service; they move directly from your address to the counterparty's address, or through a contract that releases them only after the other side of the trade is confirmed.
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The core mechanism: Atomic swaps
The most common method is the atomic swap. It uses a cryptographic primitive called a hash time-locked contract (HTLC). You create a transaction that locks your coins with a hash of a secret. The counterparty locks their coins with the same hash. You then reveal the secret to claim their coins. If either side fails to act within a time window, the locked coins return to their original owner.
This works because neither party can cheat. You cannot take the counterparty's coins without revealing the secret that also releases your coins to them. The service acts as a coordinator - it generates the secret, passes the hash to both sides, and watches the blockchains for confirmations. It never touches the private keys.
Cross-chain swaps without a bridge
When the two blockchains do not support the same scripting language, the service uses a relay or a notary mechanism. One chain's smart contract can verify a simplified payment proof from the other chain. The service runs nodes that monitor both chains and trigger the contract when the proof is valid. Your funds still move directly between your wallet and the contract; the service only sends the proof.
Some services use a "swap wallet" approach, but still non-custodially. You generate a fresh deposit address from a deterministic wallet that you control. The service reads the blockchain for incoming transactions to that address. When it sees enough confirmations, it sends your target coins from its own liquidity pool to the address you provided. The service never holds your private keys. It risks its own liquidity on the assumption that your incoming transaction will not be reversed.
The role of the service's hot wallet
There is a common misconception that the service must hold your coins temporarily. In a well-designed non-custodial swap, it does not. The service may maintain a hot wallet to pay transaction fees or to handle the outgoing side of a swap when the incoming side is already confirmed. That wallet is funded by fees collected from previous swaps. It is not your wallet. You do not send funds to it.
Confirmation requirements and finality
The swap service waits for a certain number of block confirmations on both chains before treating a transaction as final. This prevents double-spends and reorganisations from causing a loss. The number of confirmations varies by blockchain - Bitcoin typically requires more than a faster chain like Solana. The service sets these thresholds conservatively. If you send your coins and they are not confirmed within the time limit, the swap expires and your coins are returned to you. The service never had custody of them.
The hub page context
This explanation assumes you understand how swaps move coins across chains in general. For a broader view of the entire process - including the distinction between bridges and swaps, and the risks each approach carries - read the hub page "Swapping crypto across chains." It covers the architectural choices that make non-custodial settlement possible or impossible.
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