Starknet Launches Private Bitcoin strkBTC to Address Privacy and Quantum Risks

Author: Castle Labs

Compiled by Deep潮 TechFlow

DeepChaohao Summary: As on-chain finance draws closer to traditional markets, two critical issues have emerged: all fund flows are publicly visible, and quantum computing poses a threat to existing cryptographic signatures. Bitcoin, the largest asset in the crypto market with a 56% share, serves as the clearest litmus test for both issues. Starknet’s strkBTC solution aims to address both visibility and longevity: enabling private Bitcoin transfers while preparing technologically for the quantum era.

As on-chain finance draws closer to traditional markets, digital assets are facing higher standards and stricter requirements.

This new world faces two critical issues: on-chain fund flows are publicly visible to everyone, and the cryptographic signatures underpinning the entire technology are vulnerable to quantum computing threats.

This is most evident on Bitcoin.

Bitcoin currently accounts for over 56% of the total cryptocurrency market capitalization and remains the anchor of the entire crypto market, despite having minimal programmability itself.

To enhance its utility and programmability, Bitcoin has been bridged across chains via wrapped tokens into the on-chain financial ecosystem.

But Bitcoin in DeFi requires more than just higher yields; it needs a way to transfer large amounts without public broadcasting, and assurance that it will remain secure even when tomorrow’s quantum computers arrive.

The same applies to other assets in on-chain finance: assets must be able to be transferred, settled, and combined without exposing individual holdings to the public, and without relying on cryptographic technologies that may not survive until the next decade.

We have been tracking a protocol that appears to have understood these issues earlier than most projects and built solutions around them.

Although Starknet launched its BTCFi initiative earlier this year, it’s more than just making Bitcoin available on-chain. It presents the first clear test case for Bitcoin as a asset that meets the conditions individuals and institutions truly care about: private by default, disclosable when necessary, and hardened for a post-quantum future.

Regarding Starknet’s work in this space, we previously reported on why $2 trillion in Bitcoin remains idle, how Starknet’s roadmap charts a path to trustless BTC, its new privacy framework STRK20, and why they designed the system to achieve privacy through ownership.

The core principle of the crypto world has always been "Don't trust, verify"—something that publicly transparent blockchains have consistently enabled us to do: verify balances, inspect transfers, track fund flows, and monitor contract interactions. Everything is open to everyone.

You can understand how it began.

Transparency builds trust, but complete transparency can compromise intellectual property, strategy, personal safety, and operational privacy. This is especially true today, as AI-driven deanonymization can link public addresses to real-world identities with up to 90% accuracy.

Privacy is not only a human right but also a critical infrastructure needed for on-chain user protection and institutional adoption.

Individuals need privacy to avoid surveillance, profiling, harassment, crime, and political exposure. Institutions need privacy to maintain the confidentiality of holdings, order flow, and other data, as well as to prevent counterparty visibility and strategy leakage. Additionally, privacy must be configurable to allow selective disclosure to auditors, regulators, or compliance departments.

Previous on-chain privacy attempts have repeatedly highlighted trade-offs:

The real-world consequences of non-compliant paths are evident in the OFAC sanctions, criminal charges, and imprisonment of developers behind purely anonymous privacy pools like Tornado Cash.

Privacy coins on native chains, such as Monero and Zcash, have demonstrated that hiding transactions is possible, but they have consistently struggled to integrate with other parts of the on-chain world and cannot be broadly combined with DeFi primitives—pointing to a larger issue beyond privacy: liquidity, interoperability, and compliance.

Privacy execution systems like Aztec identified early demand for private DeFi, but they often faced high costs, fragmented liquidity, and poor user experiences.

Problems caused by lack of privacy extend beyond isolated on-chain worlds and have infiltrated the physical world. On-chain addresses tied to real individuals and public balances increase the risk of attacks. According to CertiK, there were 34 verified physical attacks against cryptocurrency holders in the first four months of 2026, a 41% year-over-year increase—representing only a fraction of these severely underreported incidents. More specifically, in France, 41 cryptocurrency-related kidnappings occurred between January and May 2026, averaging one every 2.5 days.

Privacy is not only about concealing transaction activity or protecting alpha, but increasingly about reducing personal and operational risk.

While privacy concerns are being actively addressed within the industry, another threat from quantum computing has emerged. Simultaneously solving visibility and persistence could bring blockchain closer to becoming the financial infrastructure of the next generation.

In March of this year, a report by Google Quantum AI, co-authored by Justin Drake (Ethereum Foundation) and Dan Boneh (Stanford University), identified multiple attack vectors and estimated that approximately $100 billion in the Ethereum ecosystem is at risk. It specifically highlighted that Starknet has a stronger post-quantum position compared to other major L2s, as its proof system is based on hash-based STARK assumptions rather than elliptic curve cryptography.

This paper focuses on secp256k1 public key exposure related to Bitcoin and Ethereum wallets, stating that a sufficiently powerful quantum computer could compromise wallets in under nine minutes. Justin Drake later warned that there is "at least a 10% chance" quantum computers will be able to recover private keys from exposed public keys by 2032.

Although this is not yet a reality today, the long-term security and lifespan of assets meant to be held for decades have come into question.

Bitcoin is the world's most important digital asset, and as it is increasingly used as collateral, a reserve, and an asset on institutional balance sheets, demands for its security and privacy are rising.

In the next section, we focus on a solution built around Bitcoin, which is the largest and clearest test case for these privacy challenges.

We have all likely used wrapped BTC tokens. They enable Bitcoin to enter other ecosystems and become composable: as tradable assets, as collateral, and as liquidity.

What they have not addressed is visibility.

Although wrapping BTC can make it productive, every movement can still be monitored, inspected, and traded against. Deposits, loans, trades, LP positions, repayments, withdrawals, wallet clusters, treasury liquidity—all are publicly visible by default.

This is not how serious financial markets operate; until this issue is resolved, on-chain finance will continue to hit an institutional ceiling.

In traditional finance, privacy is built into the infrastructure, whether you're a retail investor or a institutional giant. In fact, a significant portion of stock trading volume flows through private or over-the-counter venues such as dark pools, where counterparties see only what they need to see, regulators retain access when necessary, and the public sees aggregated trading volumes rather than every real-time movement.

Cryptocurrencies treat visibility as the standard. In reality, privacy should be the norm.

strkBTC is Starknet's attempt to enable Bitcoin to flow within the on-chain financial world without such restrictions.

strkBTC is an ERC-20 token on Starknet, backed by BTC locked on the Bitcoin network, and built on StarkWare’s privacy framework STRK20 for shielded balances and private transfers.

STRK20 offers two modes for strkBTC:

In public mode, it behaves like a standard ERC-20 token: users can hold, transfer, supply to lending markets, provide liquidity, or use it as collateral.

In shielded mode, selected balances and transactions are hidden from public view. Users can shield, privately transact, and unshield directly from their wallet to return balances to public view.

Before the Starknet v0.14.2 upgrade, which enabled STRK20, applications wishing to verify STARK proofs on Starknet had to perform this within smart contracts, making it costly and complex due to the size of the proofs. Now, transactions can directly reference off-chain proofs, and Starknet consensus handles proof verification natively through protocol-integrated validation.

This enables privacy at the protocol level, eliminating the historical friction of relying on separate apps, chains, pools, or mixers, which add complexity, cost, and liquidity fragmentation. This allows applications to focus on building better products, as the underlying infrastructure makes private operations easily accessible to developers.

Compliance is a key part of the design, which is part of opening Starknet to on-chain institutions.

When a user blocks strkBTC, the associated viewing key is shared with Financial Privacy Inc. (also known as FPI), an independent third-party audit firm operating the compliance infrastructure for STRK20, which is granted scoped access under valid regulatory requests. While this may conflict with pure cypherpunk philosophy, it aligns much more closely with traditional markets: public privacy, disclosed to regulators.

The bridge follows a similar logic and is operated by a trusted strkBTC consortium consisting of Twinstake, NEAR Intents, Luganodes, UTXO Management, and Xverse. Currently, these independent signers support the minting and burning of BTC and strkBTC. The consortium is not the final state; however, Starknet is committed to progressively strengthening the roadmap over time.

strkBTC is not meant to become another wrapped token, but to unlock the potential of programmable, composable BTC whose movements are not broadcast, thereby addressing the first issue: visibility.

The next question is persistence.

Every blockchain relies on public-key cryptography. When users sign transactions, they reveal their public key while keeping their private key hidden. This is standard practice in Bitcoin and most other blockchains and is considered completely normal and secure in today’s environment. However, in a post-quantum world, this assumption becomes somewhat unstable.

As previously mentioned, a quantum computer powerful enough to run Shor's algorithm could theoretically derive private keys from exposed public keys. This means that public keys—the harmless part of transaction verification—could soon become a potential attack surface. This is not unique to any single chain, as the same elliptic curve foundation underlies Bitcoin, Ethereum, and Solana.

Threats are shared, but the ability to respond is not. The most exposed chains are often the slowest to move, and Bitcoin is the clearest example.

Bitcoin is not lacking in ideas for a post-quantum future. If anything, it has too many. The challenge is reaching consensus on the trade-offs the network is willing to accept: larger signatures, higher costs, handling legacy coins, user migration, wallet support, miner policies, or fighting to freeze dormant and unmigrated coins.

Clearly, Bitcoin's issues are both technical and sociopolitical.

One of the co-authors of the Google paper, Dan Boneh, recently calmed everyone down in an interview: "Bitcoin should not panic, but it also shouldn't be ignored. Acting too quickly could be worse than waiting, as a hasty post-quantum migration might introduce catastrophic errors before quantum computing becomes a real threat."

Bitcoin may solve its quantum problem, but not quickly or cleanly.

This sluggishness is, to some extent, a feature of sound money, but it also leaves the door open. While the base layer debates, more agile stacks can build durability that Bitcoin itself cannot yet promise.

Ethereum and its Layer 2 extensions cannot escape this issue. Most rollups settle on Ethereum and rely on it for data availability, thereby inheriting the underlying layer’s exposure. Ethereum is aware of this and has released its own multi-year migration plan, but until that plan is implemented, every chain built on top of Ethereum remains exposed to Ethereum’s post-quantum migration risks.

This is where Starknet leads. Although it settles to Ethereum like any other Layer 2, its core—the proof layer—is built on cryptography that does not rely on quantum-vulnerable techniques. While the exposure inherited from Ethereum is real, everything within Starknet’s own stack carries less migration debt than most major chains, and it has more innovations in the pipeline.

Starknet's dominant position stems from two design choices made before quantum computing became an urgent concern.

The first is the proof layer—the system that generates STARK proofs to secure every state transition on the network. It relies on hash functions rather than elliptic curve mathematics, which is vulnerable to quantum computers—a design established since 2018 in the paper co-authored by StarkWare CEO Eli Ben-Sasson. This is the critical security layer, and it’s why Google’s paper lists Starknet as the only major Layer 2 that is already ahead.

The second is native account abstraction. On most chains, signature schemes are fixed at the protocol level, so replacing them requires a hard fork that every user and application must adopt. Starknet, however, allows accounts to define their own authentication methods, enabling users to migrate to quantum-resistant signatures without changing the protocol layer. According to StarkWare, a quantum-resistant wallet called S2morrow has already been deployed using Falcon-512, and OpenZeppelin is building a standardized version.

On many chains, this change means coordinating a full protocol migration. On Starknet, much of the work can begin with wallet upgrades. This does not mean every Starknet wallet is quantum-resistant, but this model provides Starknet users with a smoother path forward.

StarkWare is now addressing the remaining gaps. Last week, they released a roadmap aiming to make Starknet end-to-end quantum-resistant before Q-day—the point at which quantum computers become powerful enough to break today’s cryptography.

The roadmap is divided into three phases:

None of this means that Starknet is fully quantum-resistant today, nor does the roadmap claim it is.

Starknet can replace Pedersen with BLAKE2 to improve quantum-resistant wallet support and provide migration paths for traditional contracts, but it cannot eliminate all issues inherited from the base layer. Bridge messages and blob data availability still depend on Ethereum’s own quantum-resistant roadmap. Starknet can strengthen the parts it controls, but the components inherited from Ethereum will progress according to Ethereum’s timeline. That said, the Ethereum Foundation has outlined structured fork milestones aimed at completing the core quantum-resistant infrastructure around 2029.

strkBTC has a similar phased story. Currently, bridging relies on a consortium to coordinate the minting and burning of BTC and strkBTC. This is a trusted starting point, but not the ideal trustless end state. Starknet’s goal is to transition from the consortium model to native Bitcoin verification, then to a less-trustful BitVM design, and ultimately, if Bitcoin enables the required opcodes in the future, to a fully trustless OP_CAT-based design.

Viewing keys are another unproven component. They represent Starknet’s practical solution for institutional privacy: publicly opaque but selectively disclosable—yet they have not been stress-tested in real-world scenarios, raising questions about who can request disclosure, under what conditions, and what safeguards are in place.

Digital assets, including Bitcoin, do not require another layer of packaging. They need the surrounding infrastructure that can operate on-chain without compromising the two things institutions care about most: current confidentiality and future durability.

strkBTC addresses privacy by providing a private, selectively disclosable pathway for BTC into DeFi. Starknet’s existing architecture and roadmap are designed for longevity: its proof layer already avoids elliptic curve assumptions that would impose quantum-resistant migration burdens on other protocols, and its roadmap now extends this advantage to the remaining components, explicitly aiming to make Starknet quantum-resistant before "Q-day."

Although the results are still in early stages, the direction is clear: the next institutional phase of on-chain finance requires more than just yield—it needs privacy, compliance, programmability, and durability all integrated into a single technology stack.