Alice Liu: Orkun, great to have you here. Thanks for taking the time.
Orkun Kılıç: Thanks for having me. Excited to be here.
Alice: Let’s start with your background. How did you first get involved in Web3 and, specifically, in ZK?
Orkun: My background is in engineering. I’ve been doing web development since high school, but in college, I discovered blockchain and smart contracts. What really got me interested was the real-world use of crypto - people sending money to each other, making real transactions. I’m from Istanbul, Turkey, where we have a lot of local exchange shops dealing in USDT to Turkish Lira conversions, so I started looking into how Bitcoin worked. The issue was that Bitcoin’s scripting language wasn’t expressive enough to build complex applications. So, like many others, I started developing smart contracts on other chains.
A year into smart contract development, I discovered ZK, which led my co-founders and me to start Chainway Labs over two years ago. We initially worked on various ZK applications, including Proof of Innocence, and then wrote a research paper on it. This hands-on experience with ZK helped us understand its potential and led us to Bitcoin development.
With the rise of Ordinals, we saw an opportunity to apply our ZK knowledge to Bitcoin, which eventually evolved into Citrea. The goal was to bring DeFi to Bitcoin using ZK and the new block space enabled by inscriptions. We've been building in this direction for over a year now.
Alice: That’s quite the journey - starting with smart contracts, moving into ZK, and now focusing on Bitcoin. You mentioned Bitcoin’s scripting limitations. How do you see the Bitcoin ecosystem evolving over the next few years, and where does ZK fit into that?
Orkun: Bitcoin has always had an application layer, even from the early days with things like Satoshi Dice and Colored Coins. But over time, the focus shifted toward Lightning and core protocol work, with applications taking a backseat.
Ordinals changed that. They’ve brought a new wave of developers to Bitcoin, experimenting with tokens, marketplaces, and exchanges. This shift is crucial because Bitcoin has lost some of its dominance over the years. It was once 100% of the crypto market but is now closer to 60%.
With Citrea, we’re trying to bring back application development in a way that leverages Bitcoin’s security and monetary properties. We’re not building new tooling from scratch - we’re bringing existing, battle-tested infrastructure like the EVM to Bitcoin via ZK. This means developers don’t need to learn a new ecosystem; they can reuse what already works, making adoption much easier.
Alice: That’s a great approach - leveraging what already exists rather than reinventing the wheel. What applications are you most excited about?
Orkun: There are a few that stand out. First, decentralized exchanges. Right now, most Bitcoin trading happens on centralized exchanges. With Citrea, users will be able to trade without trusting an intermediary. Second, Bitcoin-backed stablecoins. Most Bitcoin users still hold fiat like USD, and when they buy Bitcoin, it’s usually through custodial solutions. A trustless, Bitcoin-backed stablecoin would allow people to hold value in Bitcoin without exposure to volatility, and they could buy BTC whenever they want without KYC or centralized exchange risk. Third, Bitcoin-backed loans. Bitcoin is an incredibly valuable asset, yet today, it can only be utilized through centralized services. A decentralized lending protocol could unlock a massive market. Lastly, prediction markets. These were originally meant to be built on Bitcoin but moved to Ethereum due to tooling limitations. With Citrea, they can finally be built on Bitcoin.
Alice: I find Bitcoin-backed collateral particularly compelling. It seems like a major value unlock. You also talked about non-custodial solutions earlier. Why are they so important, and what are some of the key use cases they enable?
Orkun: Bitcoin was designed as a peer-to-peer electronic cash system, but today, most people use custodial solutions. Whether it’s centralized exchanges or custodial Lightning wallets, people are holding Bitcoin through intermediaries, which goes against Satoshi’s original vision. The problem is usability. Setting up a Lightning node is hard. Managing private keys and liquidity is complex. That’s why many Bitcoin users have shifted to custodial solutions - they’re just easier to use.
What we’re doing with Citrea is improving the developer experience so they can build better user-friendly applications. Ethereum already has great self-custody solutions, like smart contract wallets and secure enclaves for key management. Bitcoin developers aren’t leveraging these yet because the tooling isn’t there. With Citrea, we’re bringing these innovations to Bitcoin so that users can hold their own keys in a way that’s both secure and easy to use.
Alice: That makes a lot of sense. Shifting gears to scalability - how do you view the trade-offs between rollups and sidechains?
Orkun: Sidechains operate as independent blockchains with their own validator sets. While they offer scalability, they lack the security properties of Bitcoin. Rollups, on the other hand, are directly tied to Bitcoin’s security model. With rollups, we can achieve fast finality, censorship resistance, and trust-minimized bridges. A key differentiator is settlement - sidechains require users to trust a multisig or federation for bridging, whereas rollups allow for trustless withdrawals via fraud or validity proofs. Ultimately, we believe users want to interact with Bitcoin, not a separate chain. That’s why we chose to build Citrea as a rollup rather than a sidechain.
Alice: What are the biggest challenges in building a ZK rollup on Bitcoin versus Ethereum?
Orkun: Ethereum already has a mature rollup ecosystem. You can launch a rollup using existing frameworks like OP Stack or ZK Stack. On Bitcoin, we have to build everything from scratch - sequencers, proof aggregation, light clients, and even contribute to BitVM development. Proof verification is particularly challenging. Ethereum has a precompile for verifying ZK proofs, while Bitcoin requires workarounds like BitVM to achieve similar functionality. This makes building on Bitcoin significantly harder, but also more rewarding.
Alice: Looking ahead, how do you see Citrea evolving? Any major updates or announcements?
Orkun: We recently announced our Series A and launched Citrea Origins, an incubation program for developers building Bitcoin applications on Citrea. It’s not just about funding - we help teams with product development, branding, community building, and go-to-market strategies. If you’re a developer interested in building on Bitcoin, I highly encourage you to apply. We’re excited to support new projects that push Bitcoin’s application layer forward.
Alice: That’s fantastic. It’s great to see more developer-focused initiatives in this space. Thanks for taking the time, Orkun. I really enjoyed this discussion.
Orkun: Likewise. Thanks for the great questions!
Follow @0x_orkun and @citrea_xyz to keep up-to-date with their work.
