Atomic Swap

Trustless peer-to-peer cryptocurrency exchange mechanism across different blockchains using Hash Time-Locked Contracts (HTLCs) that guarantees atomic execution where the swap either completes fully or not at all, eliminating counterparty risk without requiring centralized intermediaries.

Semantic Classification

Content

Definition

• Trustless peer-to-peer exchange of cryptocurrencies across different blockchains without intermediaries

• Uses Hash Time-Locked Contracts (HTLCs) ensuring atomicity: swap completes fully or not at all

• Enables decentralized cross-chain trading without centralized exchanges

  Core Components

• Hash Time-Locked Contract (HTLC): Smart contract with hash preimage and timeout

• Secret/Preimage: Random value known only to initiator

• Hash Lock: Cryptographic hash of secret used as condition

• Time Lock: Expiration deadline for claim/refund

  Technical Characteristics

• Atomicity: All-or-nothing execution guarantee

• Trustlessness: No third-party custody of funds

• Cross-Chain: Works between independent blockchains

• Non-Custodial: Users maintain control until swap completion

  Protocol Flow

  1. Initiation: Alice creates HTLC on Chain A with hash(secret)
  2. Response: Bob creates HTLC on Chain B with same hash
  3. Claim: Alice reveals secret to claim Bob’s funds on Chain B
  4. Complete: Bob uses revealed secret to claim Alice’s funds on Chain A
  5. Refund: If timeout expires, both parties reclaim funds

  Implementation Methods

• On-Chain HTLCs: Native smart contract support (Ethereum, etc.)

• Bitcoin Script: Using OP_CHECKLOCKTIMEVERIFY and OP_CHECKSEQUENCEVERIFY

• Lightning Network: Off-chain atomic swaps via payment channels

• Submarine Swaps: On-chain to off-chain atomic swaps

  Use Cases

• Decentralized cryptocurrency exchanges

• Cross-chain arbitrage

• Privacy-preserving trades

• Interoperability between blockchain ecosystems

  Examples

• Bitcoin Proof-of-Work Protocol ←> Litecoin atomic swaps

• Ethereum Smart Contract Platform ←> ERC-20 Token swaps

• Lightning Network cross-chain swaps

• Polkadot parachain swaps

  Relationships

  Security Properties

• No counterparty risk after setup

• No third-party custody

• Cryptographic guarantee of atomicity

• Time-based refund mechanism

  Advantages

• Trustless cross-chain exchange

• No exchange custody risk

• Censorship-resistant

• Privacy-preserving (no KYC)

  Limitations

• Both parties must be online during swap

• Requires blockchain support for scripting/smart contracts

• Time lock duration trade-offs (security vs capital efficiency)

• No price discovery mechanism

• User experience complexity

  Performance Considerations

• Multi-step confirmation process

• Total time = 2x confirmation time (both chains)

• Capital lockup during swap duration

• Gas costs for smart contract execution

  Variants

• American Call Option: Time-asymmetric atomic swaps

• Adaptor Signatures: Scriptless atomic swaps using signatures

• Threshold Signatures: Multi-party atomic swaps

• Cross-Chain AMMs: Automated market makers for atomic swaps

  HTLC Parameters

• Hash Function: SHA256, RIPEMD160

• Time Lock: Typically 24-48 hours

• Confirmation Requirements: Chain-specific finality

• Refund Buffer: Time margin between chain A and B locks

  Related Concepts

• Hash Time-Locked Contract

• Cross-Chain Bridge

• Decentralized Exchange

• Payment Channel

  blockchain atomic-swap interoperability cross-chain

  Relationships

Provenance