Developers and users alike have sought seamless interaction between platforms without having to rely on centralized bridges or third-party services, and the Internet Computer Protocol (ICP), developed by the DFINITY Foundation, is making this vision a reality through a powerful concept known as Chain Fusion.

Chain Fusion allows smart contracts (canisters) on the Internet Computer to directly interact with other blockchains, Bitcoin, Ethereum, and now, Solana, without intermediaries. This level of interoperability redefines what decentralized applications can do, especially when multiple blockchains are involved.

Introducing Chain Fusion

When the Internet Computer launched in 2021, it introduced a radically different infrastructure for hosting smart contracts and internet services. But in a world of competing ecosystems, Bitcoin for its pristine store of value, Ethereum for DeFi, and Solana for high-throughput applications, no single chain could cover all use cases.

To address this, DFINITY introduced Chain Fusion, a framework that allows ICP’s canisters to directly read and write to other blockchains using cryptographic integrations rather than traditional bridges. The protocol’s first milestones were:

• Chain-key Bitcoin (ckBTC): Introduced secure, wrapped BTC directly on the IC, with ICP nodes able to sign native Bitcoin transactions.
• Chain-key Ethereum (ckETH): Enabled Ethereum interaction without MetaMask, RPC relays, or oracles.

Now, the integration of Solana, a fast and cost-efficient blockchain, expands the reach of Chain Fusion even further.

IC-SIWS: Solana Wallet Authentication on ICP

The forefront of Solana's integration with ICP is the IC-SIWS project (Sign-In With Solana), developed by Kristofer Lund. This project isn’t just about interoperability, it’s about identity and authentication.

IC-SIWS allows any ICP-based application to support Solana wallet-based logins. Just as websites today support Google or Apple logins, decentralized applications on ICP can now authenticate users directly through their Solana wallets. This enhances accessibility and security while also providing a consistent user experience across platforms.

What IC-SIWS Brings to the Table

• Solana Wallet Sign-In: Users can log into ICP apps using any Solana wallet (like Phantom), generating a delegated Internet Identity under the hood.
• Consistent Identity Mapping: Each Solana address maps to a consistent ICP principal (identity), ensuring that logins are predictable across devices.
• Session Isolation: Prevents cross-app identity leakage by generating app-specific session identities.
• Timebound Sessions: Adds a security layer by allowing sessions to expire.
• Prebuilt Canisters: Developers can integrate a ready-made identity provider without building custom infrastructure.

The project mirrors its Ethereum counterpart, IC-SIWE (Sign-In With Ethereum), but tailors its cryptographic handling and message signing to Solana’s unique architecture. Together, these libraries create a multi-chain authentication standard for the Internet Computer.

How This Works

The authentication flow is straightforward and developer-friendly:

1. The frontend uses the ic-siws-js library to request a login message from the canister.
2. The canister generates and returns a SIWS message.
3. The frontend prompts the user to sign this message with their Solana wallet.
4. The signed message is sent back and verified by the canister.
5. Upon successful verification, the canister issues a delegated ICP identity.
6. The frontend uses this identity to authenticate interactions with other ICP canisters.

This process makes it possible to interact with decentralized applications on ICP using nothing but your Solana wallet, no new extensions, no new accounts.

Tools and Integration

To make integration easy, the IC-SIWS project is split into three core components:

• ic_siws (Rust Library): For full control over backend logic, including signature verification and principal generation.
• ic-siws-provider (Prebuilt Canister): A plug-and-play identity service that handles authentication out of the box.
• ic-siws-js (Frontend Library): Works with frameworks like React, Vue, and Svelte, making it easy to add Solana login buttons to your app.

Demo applications are already live across multiple frameworks, providing developers with hands-on examples of how to implement this technology.

Why Solana Integration Matters

Solana’s appeal lies in its low fees and high throughput, making it a natural choice for consumer-facing apps, gaming, and DePIN solutions. By bringing Solana into the Chain Fusion framework, ICP dapps gain access to:

• A large, active Solana user base.
• Lightning-fast transactions at low costs.
• A growing ecosystem of tokens, NFTs, and DeFi products.

Meanwhile, Solana dapps can now tap into ICP’s scalable smart contracts, stable gas fees (via cycles), and on-chain storage capabilities. The synergy opens doors for fully decentralized, multi-chain applications that simply weren’t possible before.

What To Anticipate On IC-SIWS

The IC-SIWS project is still evolving, but its progress is impressive. Future plans include:

• Enhanced support for Solana-specific features such as token gating and DePIN onboarding.
• Deeper integration with Solana’s on-chain programs via RPC canisters.
• Inclusion in decentralized identity standards and multi-chain wallets like OISY, DFINITY’s new universal wallet.

The work being done here lays a foundation for truly fluid user experiences in Web3. Rather than thinking in terms of separate chains, we’ll think in terms of user identities and applications, regardless of the underlying network.

Conclusion

With Chain Fusion, ICP is building a world where applications aren’t bound by blockchain borders. The IC-SIWS project pushes that vision further by making multi-chain identity as seamless as logging in with a password.

As developers begin to adopt this technology, expect to see dapps that connect Solana's speed with ICP’s infinite scalability, all without sacrificing decentralization.

The age of fragmented blockchain ecosystems is ending. IC-SIWS is proof that a unified, multi-chain internet is not just possible, it’s already here.