1sync

1Sync is a decentralized, trustless cross-chain swap platform that allows users to securely exchange tokens between Ethereum (EVM-compatible chains) and Stellar without the need for centralized exchanges or custodial bridges. By combining smart contracts on Ethereum with Stellar’s native Claimable Balance functionality, 1Sync facilitates seamless, atomic asset transfers across blockchain ecosystems. The core innovation lies in synchronizing transaction states between two fundamentally different blockchain environments using hashlocks and timelocks enabling bi-directional, verifiable swaps that are either fully completed or fully refunded if any step fails.

The platform uses the atomic swap concept based on Hashed Timelock Contracts (HTLCs). A swap begins when the maker creates an order on the platform, defining the assets, counterparties, expiration time, and a secret hashlock. The taker then agrees to this order and locks their portion of the funds typically XLM on the Stellar blockchain using a Claimable Balance that is claimable only if the secret preimage is revealed within a specified time.

Once the taker has secured the funds on Stellar, the maker proceeds to lock their ETH (or ERC-20 tokens) on Ethereum using a smart contract deployed on the Sepolia testnet. This contract enforces the same hashlock and expiration logic. After these conditions are met, the maker uses their secret to claim the XLM on Stellar. In doing so, the secret becomes public, allowing the taker to retrieve the ETH from the Ethereum contract. If either party fails to follow through within the timelock period, the funds become refundable to the original sender.

From a technical standpoint, 1Sync integrates MetaMask for Ethereum transactions and Freighter Wallet for Stellar interactions. The frontend (React + TypeScript) provides users with a step-by-step guided interface that updates the swap status in real-time—whether it’s “created,” “filled,” “escrowed,” “funded,” “claimed,” or “completed.” The backend (Node.js/Express) acts as a coordination layer between the UI and the blockchains, managing order creation, transaction tracking, and relaying signed transaction hashes to complete swaps.

The smart contracts on Ethereum are standard HTLC contracts that store the swap value, hashlock, timelock, and recipient. On Stellar, Claimable Balances serve a similar role but are implemented through transaction constraints and claim predicates. This hybrid approach avoids the need for complex custom contracts on Stellar (such as Soroban), simplifying development and making the system more compatible with current wallet infrastructure.

1Sync is ideal for users who want to move assets between Ethereum and Stellar ecosystems while maintaining full custody and minimizing counterparty risk. Potential use cases include cross-chain remittances, arbitrage opportunities, or decentralized token bridging for DeFi applications. The design prioritizes transparency, security, and usability, with clear error messages, on-chain transaction tracking, and robust state management.

In summary, 1Sync is a fully functional atomic swap platform bridging Ethereum and Stellar using proven cryptographic principles. It demonstrates a working example of interoperable Web3 protocols and offers a safer, decentralized alternative to custodial bridges empowering users to retain control of their assets while transacting across chains.

1Sync is built using a hybrid of Solidity HTLC contracts on Ethereum (Sepolia) and Claimable Balances on Stellar Testnet. The frontend is in React (TypeScript) with MetaMask and Freighter wallet integrations, while the backend is powered by Node.js + Express, coordinating swap states and cryptographic validations. We used Ethers.js and stellar-sdk for blockchain interactions. A notable hack was mimicking HTLC behavior on Stellar using preimage-locked Claimable Balances. MetaMask transaction prompts had to be wrapped in user-triggered events to bypass silent failures. The system enables bi-directional, trustless swaps between chains without custodial bridges.