Tech Talk: Reilabs

What if you could verify a passport, prove your identity, or conduct private transactions on Solana for pennies instead of thirty dollars? At Breakpoint 2025, Reilabs unveiled Sunspot—a game-changing toolchain that slashes zero-knowledge proof verification costs by orders of magnitude, finally making ZK cryptography practical for everyday Solana applications.

Summary

Zero-knowledge cryptography has long promised revolutionary capabilities for blockchain applications: private transactions, identity verification without data exposure, and secure web2 integrations. However, the technology has remained largely impractical on Solana due to prohibitive verification costs. Previous attempts to implement ZK proof verifiers on-chain required around $30 in rent costs just to verify a single proof—a non-starter for any real-world application.

Marcin Kostrzewa from Reilabs presented Sunspot as the solution to this fundamental problem. The toolchain allows developers to write circuits in Nuar, a Rust-like programming language developed by Aztec that's quickly becoming the standard for ZK development, while leveraging a different proof system called Gnark for on-chain verification. This hybrid approach dramatically reduces proof sizes and verification costs while maintaining the developer-friendly experience that Nuar provides.

The practical implications are substantial. Sunspot produces proofs of just 388 bytes—small enough to fit comfortably within Solana's transaction size limits while leaving 600 bytes for additional business logic. Verification costs clock in at under 500,000 compute units, making real-world applications economically viable. As a demonstration, Reilabs built an application that uses ZK Passport to mint SPL tokens to users who prove they're not from sanctioned countries—all without revealing any other personal information.

The toolchain positions Solana to capture use cases previously impossible on the network, from institutional-grade private transactions to on-chain games with true fog-of-war mechanics. With institutions increasingly interested in blockchain but concerned about transaction visibility, and gaming applications requiring hidden game states, Sunspot opens doors that were previously locked.

Key Points:

Why Zero-Knowledge Cryptography Matters for Solana

Zero-knowledge proofs enable a category of applications that are nearly impossible to build any other way. For private transactions, this goes beyond controversial mixers—it addresses a critical need for institutional adoption. Financial institutions are reluctant to conduct business on public blockchains where chain analysis companies can track every transaction, revealing trading strategies and portfolio movements. ZK cryptography allows them to transact with privacy while still maintaining compliance.

Beyond finance, gaming applications benefit enormously. Any on-chain game with hidden information—like fog of war where players shouldn't see the entire map—requires zero-knowledge proofs to verify that players follow game rules without revealing their positions or strategies. This isn't a nice-to-have feature; it's fundamental to making certain game genres possible on blockchain.

The Previous Cost Problem and Technical Breakthrough

The core challenge Reilabs solved was the mismatch between Nuar's proof system (Bartenberg) and Solana's constraints. While Bartenberg proofs aren't large by general ZK standards, they're far too expensive for Solana verification. Someone built an on-chain verifier and discovered it cost $30 in rent alone to verify a single proof—making any application economically impossible.

Sunspot's innovation is a translation layer that accepts circuits written in Nuar but outputs proofs in Gnark, which uses an enhanced version of Groth16 (dubbed "Groth16++"). This enhanced system supports lookup arguments, which are essential for bitwise operations, memory checking, and traditional cryptography primitives. The toolchain then auto-generates a Solana verifier program, creating an end-to-end pipeline from development to deployment.

Identity Verification Without Data Exposure

ZK Passport represents one of the most immediately practical applications enabled by Sunspot. Traditional KYC requires collecting sensitive personal data—passport numbers, addresses, birth dates—creating privacy risks and compliance burdens. ZK Passport allows users to scan their passport's NFC chip and generate a proof containing only the specific claims needed: "I am not from a sanctioned country" or "I am over 18 years old."

The demo application Reilabs built proves this concept works at production scale. A user taps their passport to their phone, generates a proof in just five seconds on a standard MacBook Pro, and can mint an SPL token that certifies their compliance status. The proof verification happens on-chain for under 500K compute units, leaving ample room for additional application logic.

Web2 Integration Through ZK TLS and ZK Email

Sunspot supports protocols that bridge traditional web infrastructure with blockchain verification. ZK TLS Notary allows users to prove that specific data existed in an HTTP session without revealing the full contents. A practical example: proving you completed a PayPal transaction without exposing your username, password, or other transaction details.

ZK Email enables similar verification for email communications. Users can prove they received or sent an email with specific contents—perhaps a transfer confirmation from a bank or a ride receipt from Uber—and generate an on-chain verifiable proof. These protocols exist in Nuar's ecosystem and are now practical to use on Solana through Sunspot.

Developer Experience and Ecosystem

Nuar is positioned as the most developer-friendly zero-knowledge programming language currently available. Its Rust-like syntax makes it accessible to the large pool of developers already familiar with Solana's primary smart contract language. This isn't incidental—lowering the barrier to ZK development is crucial for adoption.

The ecosystem around Nuar is growing rapidly, with popular projects either migrating to it or building from scratch on the platform. Libraries and building blocks are becoming available, meaning developers don't need to implement cryptographic primitives from scratch. Sunspot plugs Solana into this growing ecosystem, giving developers access to tools and resources that are continuously improving.

Facts + Figures

• Previous on-chain ZK verifiers on Solana cost approximately $30 in rent to verify a single proof
• Sunspot reduces proof size to just 388 bytes
• Verification costs less than 500,000 compute units
• Proof generation takes approximately 5 seconds on a MacBook Pro
• After proof data, developers still have 600+ bytes available for business logic within Solana's transaction limits
• Sunspot uses Gnark/Groth16++ for verification while allowing development in Nuar
• The demo application uses ZK Passport to verify users are not from sanctioned countries
• Nuar is developed by Aztec and features Rust-like syntax
• The toolchain auto-generates Solana verifier programs from Nuar circuits
• Groth16++ supports lookup arguments essential for bitwise operations and cryptographic primitives

Top quotes

• "The Bartenberg proof system, which underlies Nuar, has really big and really expensive to verify proofs... Someone actually built a verifier on chain and just the rent cost was 30 bucks to verify a single proof."

• "Institutions are not going to be super happy about everyone, every chain analysis company being able to see what they're doing, what they're buying, what they're selling."

• "If you are building an on-chain game, you probably have the concept of some sort of fog of war... This is also something that's enabled and really only possible with zero knowledge cryptography nowadays."

• "It's 500K compute units to verify an entire passport and actually do something that you would normally offer to a KYC provider."

• "I call it the Groth16++ because it actually gives you more power."

• "The proof size is 388 bytes, which for Solana, with your one kilobyte limit of transaction size, this is really good."

• "Build something today. And I mean today. I know it's a conference, but build something today."

Questions Answered

What is Sunspot and who created it?

Sunspot is a toolchain developed by Reilabs that enables practical zero-knowledge cryptography on Solana. It allows developers to write ZK circuits in Nuar, a developer-friendly programming language, while using a different proof system (Gnark/Groth16++) for on-chain verification. The toolchain bridges the gap between the best development experience available in ZK and the practical constraints of deploying on Solana, automatically generating verifier programs that can be deployed on-chain.

Why couldn't ZK proofs work on Solana before?

The proof system underlying Nuar, called Bartenberg, produces proofs that are too large and expensive to verify on Solana. Previous attempts to build on-chain verifiers resulted in rent costs of approximately $30 per proof verification—a cost that made any real-world application economically impossible. Sunspot solves this by translating Nuar circuits into a different proof system that produces much smaller proofs and requires far fewer compute units to verify.

What practical applications does Sunspot enable?

Sunspot enables several categories of applications: private transactions for institutions concerned about on-chain visibility; identity verification through ZK Passport that proves specific claims without revealing personal data; web2 integrations through ZK TLS and ZK Email that can verify web activity without exposing sensitive credentials; on-chain games with hidden information like fog of war; and scaling solutions like ZK compression. Each of these was either impossible or impractical on Solana before this breakthrough.

How does ZK Passport work with Sunspot?

Users tap their passport's NFC chip to read its cryptographic data, then generate a zero-knowledge proof that certifies specific claims—such as not being from a sanctioned country or being over 18 years old. This proof can be verified on-chain without revealing any other personal information from the passport. The entire proof generation takes about 5 seconds on a standard laptop, and verification costs less than 500K compute units on Solana.

What programming skills do I need to use Sunspot?

Developers need familiarity with Nuar, which has a Rust-like syntax making it accessible to anyone who has worked with Rust or Solana's native development environment. The ecosystem includes growing libraries and building blocks, so developers don't need deep cryptographic expertise to build applications. Sunspot handles the complex translation between proof systems automatically, and generates the Solana verifier programs needed for deployment.