DLT Interoperability — Stellar Soroban–Polygon Asset Bridge

Overview

An EEA-compliant interoperability solution bridging Stellar Soroban and Polygon PoS, enabling cross-chain digital asset transactions. The initial use case — purchasing Soroban-based digital assets from the Polygon network — validates the bridge's core functionality and establishes a foundation for more complex institutional asset transfers.

Target Customers: Banks and Licensed Financial Institutions

Technology: Stellar Soroban, Polygon PoS, Wanchain Messaging Bridge

The Challenge

The growing adoption of distributed ledger technology and digital assets across global financial markets has made cross-chain interoperability one of the most pressing unsolved problems in the space. Institutions, technology providers, and regulators are increasingly operating across multiple DLT networks — but without common standards, each integration is bespoke, fragile, and difficult to scale.

The specific technical challenge in this engagement was bridging two structurally incompatible blockchain ecosystems: Stellar Soroban and Polygon PoS. Despite both networks supporting smart contracts and digital asset management, they differ in almost every underlying dimension:

• Consensus mechanisms: Stellar uses the Stellar Consensus Protocol (SCP), a construction of Federated Byzantine Agreement (FBA), while Polygon employs a traditional Proof of Stake system with staked validator-based block production.
• Smart contract languages: Soroban contracts are written in Rust; Polygon contracts are written in Solidity for the Ethereum Virtual Machine (EVM). Cross-chain messaging required compatible function signatures and data types across both.
• Event storage: Soroban stores event data in an env construct; EVM stores it in transaction logs. Message relayers needed to parse and repackage event data into formats acceptable to the target chain.
• Wallet incompatibility: The two networks use different public/private key mechanisms, making native wallet interoperability impossible. Metamask was used for the EVM chain and Freighter wallet for Soroban.
• Absence of a common standard: Without an open, ratified interoperability standard, any bridge implementation risked vendor lock-in, fragmentation, and insufficient trust for institutional and regulated use cases.

The Solution

The engagement addressed these challenges by designing and implementing a cross-chain asset bridge in full compliance with the EEA DLT Interoperability Specification — an open standard developed by the EEA Cross-chain Interoperability Working Group to govern asset transfers, cross-chain messaging, and action initiation across heterogeneous DLT networks.

The solution architecture centred on the Wanchain Messaging Bridge (WMB) as the decentralised cross-chain messaging infrastructure, with smart contracts deployed on both Stellar Soroban and Polygon PoS to manage asset locking, minting, verification, and ownership transfer. Crucially, the implementation was designed to update asset ownership records on the respective networks rather than physically moving assets — reducing complexity and counterparty risk while preserving security and regulatory compliance.

Implementation

Standards Analysis & EEA Specification Alignment

Working Group co-leadership contributed to the analysis of the EEA DLT Interoperability Specification's adaptability to the Stellar Soroban architecture — covering block-based consensus mechanisms, supported messaging types, cryptographic compatibility, and bridge interface design. This analysis confirmed that the specification's event-based messaging model and cryptographic framework (supporting ED25519, SECP256K1/ECDSA, EdDSA, and Keccak256) were compatible with both networks, and defined the integration approach accordingly.

Wanchain Messaging Bridge Integration

The Wanchain Message Bridge served as the core cross-chain messaging layer, designed in compliance with the EEA specification. The WmbGateway smart contract — the main entry point of the bridge — facilitates cross-chain messages between networks, leveraging the OpenZeppelin library for security. The IWmbGateway interface enabled standardised message routing between Polygon and Stellar without requiring custom point-to-point integration logic.

Cross-Chain Process Flow

The implemented transaction flow for the initial NFT use case operated as follows:

1. Seller lists asset on Stellar Soroban: The seller interacts with the WbmApp contract to list the NFT. The contract locks the asset on Stellar and sends a cross-chain sell message to the Polygon smart contract, marking it as listed for sale.
2. Buyer initiates purchase on Polygon: A buyer on the Polygon network identifies the listed asset and triggers a purchase. The minting process emits an event signalling intent to acquire the asset.
3. Cross-chain message sent from Polygon to Stellar: The Message Bridge contract on Polygon captures the purchase event, packages the data into a cross-chain message, and transmits it to the Stellar network via the Wanchain Message Bridge infrastructure.
4. Verification on Stellar: The ICrosschainVerifier contract on Stellar receives and verifies the authenticity and integrity of the incoming message, confirming that the Polygon purchase was legitimately completed.
5. Asset locked on Stellar: Following successful verification, the WbmApp contract on Stellar marks the asset as sold, preventing further sale or transfer within the Stellar network.
6. Minting confirmation on Polygon: The buyer receives a newly minted NFT on Polygon, fully linked to the original Stellar asset — establishing verified cross-chain ownership.
7. (Optional) Asset redemption on Stellar: If the buyer holds a Soroban wallet, they can initiate a redemption process to reclaim the underlying asset on Stellar. A cross-chain message is sent from Polygon to Stellar, verified through the same mechanism, and upon success the asset is unlocked and transferred to the buyer's Soroban wallet.

Atomic Settlement Architecture

The bridge implementation used multi-signature verification to ensure decentralised trust of message relayers. The architecture was designed to be extensible to full atomic settlement via Hash Time Lock Contracts (HTLCs), where only the holder of a secret key can unlock a transaction on the target chain — eliminating counterparty risk and guaranteeing settlement finality across both networks.

Outcomes

• First EEA-compliant Stellar–Polygon asset bridge delivered: The engagement produced a working, standards-compliant bridge between two architecturally distinct DLT networks — validating the EEA specification's adaptability beyond EVM-native environments and demonstrating its practical applicability in a non-trivial cross-chain context.
• Open standard proven in production context: The successful test deployment demonstrated that the EEA DLT Interoperability Specification provides a viable, reusable framework for enterprise-grade cross-chain solutions — reducing the need for bespoke integrations and the fragmentation that results from competing vendor implementations.
• Enhanced liquidity and market reach for Stellar-based assets: By enabling Polygon PoS buyers to transact with Stellar Soroban assets, the bridge expanded the addressable market for Stellar-native assets into the broader Ethereum ecosystem — directly improving liquidity access for institutional issuers operating on Stellar, such as those running tokenised fund structures.
• Institutional trust strengthened through standards compliance: Adherence to EEA standards provided a framework that regulated institutions, financial authorities, and enterprise stakeholders could evaluate against known compliance criteria — increasing the solution's credibility and adoption potential in regulated environments.
• Cryptographic security and ownership integrity maintained: The implementation of multi-signature verification, cryptographic proofs (ECDSA/EdDSA), and the optional HTLC extension path ensured that cross-chain transactions met institutional-grade security requirements, with no direct asset movement required to transfer ownership.
• Open-source contribution to the ecosystem: Wanchain, in collaboration with QualitaX, committed to releasing the cross-chain messaging framework as an open-source project — enabling third-party developers to build interoperable decentralised applications across heterogeneous blockchain architectures using the same standards-compliant foundation.
• Research leadership recognised by the EEA: The case study was published on behalf of the EEA DLT Interoperability Working Group, with QualitaX named as lead author and co-chair — establishing QualitaX as a recognised contributor to enterprise blockchain standards development at an international level.