What Are Atomic Swaps and How Do They Work?

An atomic swap is an exchange of cryptocurrencies from separate blockchains without using a third party or centralised exchange.

Table of Contents

  • Definition of Atomic Swaps
  • Key Components of Atomic Swaps
  • Step-by-step process of how Atomic Swaps Work
  • Advantages of Atomic Swaps
  • Limitations and Challenges of  Atomic Swaps
  • Real-World Applications of Atomic Swaps
  • Popular Platforms Supporting Atomic Swaps
  • FAQs


What is an atomic swap?

An atomic swap is an exchange of cryptocurrencies from separate blockchains. Atomic swaps allow the direct exchange of cryptocurrencies between two parties without needing a trusted third party or centralised exchange. The general idea is to remove centralised intermediaries like regulated exchanges and give token owners total control.

via GIPHY

Atomic swap exchanges and blockchains use smart contracts to secure transactions, ensuring that they either complete successfully for both parties or do not occur at all. Smart contracts are programs within blockchains that execute when certain conditions are met. In this case, the conditions are that each party agrees to the transaction before a timer runs out. Using a smart contract in the trade prevents either party from stealing a cryptocurrency from the other.

The term atomic implies indivisibility and completeness; it either happens or doesn't—there is no other alternative.

Atomic swaps are also called cross-chain atomic swaps.

Key Components of Atomic Swaps

To understand how atomic swaps function, it's essential to examine their key components. These components work together to ensure the swap is secure, trustworthy, and efficient.

Hash Time-Locked Contracts (HTLCs)

Atomic swaps use Hash Timelock Contracts (HTLC) to automate the exchange of tokens. As its name denotes, HTLC is a time-bound smart contract between parties that involves generating one cryptographic hash on each end.

This smart contract mechanism is crucial for securing the transaction and ensuring that it is either fully completed by both parties or not executed at all. The HTLC has two primary features: the hashlock and the timelock.

Cryptographic Hash Functions

Cryptographic hash functions play an important role in the functioning of HTLCs. A hash function takes an input (or 'message') and returns a fixed-size string of bytes, typically a hash value. The critical properties of these functions are:

  • Determinism (the same input always produces the same output).
  • Quick computation.
  • Preimage resistance (difficulty in finding an input that maps to a specific output).
  • Collision resistance (difficulty in finding two different inputs that produce the same output).

In cryptocurrency atomic swaps, the hash function ensures that only the party with the correct preimage (the secret) can complete the transaction; this secures the swap.

Photo by Traxer on Unsplash

Cross-Chain Compatibility

For an atomic swap to be possible, the two cryptocurrencies involved must support the same cryptographic hash functions and timelock functionalities. This cross-chain compatibility contributes to the swap's successful execution. Bitcoin and Litecoin, both of which use similar cryptographic primitives, are commonly used in atomic swaps. The compatibility ensures that HTLCs can be implemented on both blockchains and facilitates the cryptocurrency atomic swap.

Communication Protocols

Communication protocols help coordinate the atomic transaction between the two parties. They manage the exchange of hashed secrets and other relevant information required for the HTLCs. The protocols ensure that both parties are synchronised and aware of the swap's progress and status.

Wallet Support

Users need wallets that can create and manage HTLCs. Wallets that support atomic swap exchanges are designed to generate the necessary cryptographic elements and interact with the blockchain to lock and unlock funds. As atomic transactions gain popularity, more wallets are being developed with built-in support for these transactions, making the process more accessible to everyday users.

Step-by-step process of How Atomic Swaps Work

Crypto atomic swap uses the Hashed Timelock Contract (HTLC), which functions as a two-way virtual safe. This contract uses a sophisticated mathematical-based encryption mechanism called a hash function. It also introduces a time constraint such that transactions are reversed when either party does not fulfil their sides of the bargain within the predefined time frame.

Another important detail you need to know about the HTLC is that it requires two cryptography or encrypted keys. They are:

Hashlock: This component ensures the transaction can only be completed with a secret key. The process begins with one party, say A, generating a random secret. A then hashes this secret and shares the hash (but not the secret itself) with the other party, B. To unlock the funds locked in the HTLC, B needs to know the secret that corresponds to the hash provided by A.

Timelock: This feature adds the deadline to the transaction. If either party fails to complete their side of the transaction within the specified timeframe, the timelock ensures that the funds are returned to their original owners. This protects both parties from potential losses if the swap is unsuccessful.

How atomic swaps work in simpler terms:

Step 1:

The two parties involved in the atomic swap, X and Y, first agree on the amount and type of cryptocurrency they want to exchange. They also agree on the time frame for the swap to be completed.

Step 2:

X generates a random number known as a secret (S). She then creates a cryptographic hash of this secret and shares the hash with Y while keeping the actual secret to herself. This hash will be used to lock the funds in the smart contract.

Step 3:

X initiates the swap by creating a transaction to lock her cryptocurrency in a smart contract on the blockchain. The Hash Time-Locked Contract (HTLC)  is programmed to release the funds to Y if he can provide the preimage of the hash (the secret S). If Y does not provide the secret within a specified time frame, the contract will return the cryptocurrency to X. This ensures that X's funds are safe even if Y changes his mind.

Step 4:

Y verifies that the terms of the HTLC created by X match their agreement. Once verified, Y creates a similar HTLC on the blockchain, locking his cryptocurrency with the hash H(S). This contract will release X's cryptocurrency to her upon the revelation of the secret S. If X does not provide the secret within the specified time frame, the contract will return the cryptocurrency to Y.

Step 5:

To claim Y's coin, X must reveal the secret S on the blockchain. Once X submits the secret to the HTLC, Y can see the secret on the blockchain.

Step 6:

With the revealed secret S, Y can now claim X's coin by providing the secret to the HTLC on the coin blockchain. Both parties have now successfully exchanged their cryptocurrencies without relying on a centralised exchange or an intermediary.

If either party fails to reveal the secret within the specified time frame, HTLCs will refund the locked funds to their original owner, ensuring they are returned safely.

Advantages of Atomic Swaps

Atomic swaps offer numerous advantages, such as:

1. Decentralisation

Atomic swaps operate on a peer-to-peer basis, eliminating the need for centralised exchanges. This decentralisation reduces dependency on central bodies that may be vulnerable to hacks, regulatory issues, or operational failures. By being independent of exchange platforms, atomic swaps offer traders complete control over their accounts and exchanges.

2. Increased Security

Atomic swaps leverage the security of blockchain technology and cryptographic principles to secure transactions. The use of HTLCs ensures that funds are either exchanged according to the agreed terms or returned to their original owners. This level of security reduces the risks associated with traditional exchanges, such as hacking or insider threats.

3. Lower Fees and Faster transactions.

Atomic swaps reduce the need for intermediary services, which often charge transaction and withdrawal fees. By bypassing centralised exchanges, users can avoid the fees typically associated with trading on these platforms, which makes atomic swaps an attractive option. The direct peer-to-peer nature of atomic swaps streamlines the process, allowing for faster trade completion.

Photo by Kanchanara on Unsplash

Limitations and Challenges of  Atomic Swaps

Understanding the drawbacks of crypto atomic swaps is crucial for users and developers who want to implement or use this technology effectively.

1. Complexity and Technical Conditions

Atomic swaps require a significant level of technical knowledge to execute correctly. The process involves understanding and implementing Hash Time-Locked Contracts (HTLCs), which can be complex for the average user.

2. Limited Compatibility

Atomic swaps are primarily compatible with cryptocurrencies that support the necessary scripting capabilities and have similar hash algorithms. However, not all cryptocurrencies can participate in atomic swaps.

3. Security Concerns

While atomic swaps are designed to be secure, they are not entirely immune to security risks. Potential vulnerabilities in the implementation of HTLCs or bugs in the underlying blockchain protocols could be exploited by malicious actors. Users must also ensure they correctly set up and manage their atomic swap crypto to avoid unintended losses.

4. Lack of a centralised platform

Regulatory uncertainty surrounding cryptocurrencies and decentralised exchanges can pose challenges to the widespread adoption of atomic swaps. Different jurisdictions have varying regulations concerning the legality and taxation of cryptocurrency transactions.

Real-World Applications of Atomic Swaps

Here are some notable real-world applications of atomic swaps:

1. Decentralised Exchanges (DEXs)

Unlike centralised exchanges, DEXs allow users to trade cryptocurrencies directly with each other, enhancing privacy and security. Atomic swaps facilitate this by enabling trustless, cross-chain transactions, which allow trades to be executed without an intermediary.

2. Cross-Chain Trading

This is particularly useful for traders who want to diversify their portfolios or access assets on different blockchains without going through the cumbersome process of using multiple exchanges.

3. Arbitrage Opportunities

Traders can leverage atomic swaps for arbitrage opportunities by exploiting price differences between cryptocurrencies on different exchanges. This leads to more efficient markets and better price alignment across exchanges.

4. DeFi Integrations

Decentralised Finance(DeFi) applications can use atomic swaps to enable users to seamlessly exchange assets within the platform, providing a more comprehensive and interconnected financial ecosystem.

Photo by DS stories

1. Atomic Wallet

Atomic Wallet is a non-custodial cryptocurrency wallet that allows users to manage over 500 coins and tokens. The platform is known for its user-friendly interface and strong security measures, including private key encryption and local storage.

2. Komodo Platform

Komodo is a blockchain platform that prioritises security and scalability. Komodo's decentralised exchange, AtomicDEX, enables cross-chain atomic swaps between various cryptocurrencies. AtomicDEX supports a wide range of assets, including Bitcoin, Ethereum, and numerous ERC-20 tokens.

3. Bitcoin Lightning Network

The Bitcoin Lightning Network, a second-layer solution for the Bitcoin blockchain, enables fast and low-cost transactions. It also supports atomic swaps, allowing users to exchange Bitcoin for other cryptocurrencies like Litecoin directly on the Lightning Network.

4. Litecoin

Litecoin has been at the forefront of adopting new technologies. It supports atomic swaps with Bitcoin and other cryptocurrencies, allowing for direct, peer-to-peer exchanges.

To Wrap Up

As the cryptocurrency market continues to grow, the role of atomic swaps in the atomic swap crypto world will likely increase, and users will be offered more options for secure and efficient trading. This technology brings us closer to a future where decentralised exchanges are normal, and users have greater control over their assets and trading activities.


Frequently Asked Questions (FAQs) About Atomic Swaps

Q: What are atomic swaps?

A: Atomic swaps are a decentralised method that allows two parties to exchange different cryptocurrencies directly without needing an intermediary or exchange.

Q: How do atomic swaps work?

A: Atomic swaps use smart contracts and cryptographic techniques, particularly hash time-locked contracts (HTLCs), to ensure that the exchange happens simultaneously, securely, and without the risk of one party defaulting.

Q: When do you need an atomic swap?

A: Atomic swaps are useful if you only have one cryptocurrency but need to use another in a transaction.

Q: What is a hash time-locked contract (HTLC)?

A: An HTLC is a type of smart contract that requires the recipient of a payment to acknowledge receiving it within a specific timeframe by generating cryptographic proof, ensuring that both parties fulfil their obligations.

Q: Why are atomic swaps considered secure?

A: Atomic swaps are secure because they use cryptographic proofs and timelocks to ensure that both parties complete the transaction simultaneously or not at all, eliminating the risk of one party cheating the other.

Q: What are the advantages of using atomic swaps?

A: Advantages include enhanced privacy, reduced reliance on centralised exchanges, lower transaction fees, and the ability to trade directly from personal wallets.

Q: Are there any limitations or challenges with atomic swaps?

A: Limitations include the complexity of the technology, limited wallet and cryptocurrency support, and the need for both parties to be online and responsive during the swap.

Q: Which cryptocurrencies support atomic swaps?

A: Bitcoin and Litecoin are cryptocurrencies that support atomic swaps.

Q: Do atomic swaps require both parties to trust each other?

A: No, atomic swaps do not require trust between parties. The use of HTLCs and cryptographic techniques ensures that the swap is either completed by both parties or not at all, minimising trust issues.

Q: How do atomic swaps benefit decentralised finance (DeFi)?

A: Atomic swaps enhance DeFi by enabling cross-chain trading and liquidity without the need for centralised exchanges, fostering a more decentralised and interoperable financial ecosystem.


Disclaimer: This article was written by the writer to provide guidance and understanding of web3/blockchain/cryptocurrency. It is not an exhaustive article and should not be taken as financial advice. Obiex will not be held liable for your investment decisions.