# FAQs

**Q1: What is the zkBTC Cross-Chain Bridge?**&#x20;

The zkBTC Cross-Chain Bridge is an innovative solution based on ZKP technology designed to enable seamless cross-chain interactions between Bitcoin and Ethereum. It’s aimed to enhance the liquidity and interoperability of cryptocurrency assets.

**Q2: What security mechanisms does the zkBTC Cross-Chain Bridge employ?**

The zkBTC Cross-Chain Bridge uses a no-pool, no-custody design where assets are managed entirely by smart contracts, eliminating reliance on any centralized entity. This security approach significantly reduces centralized risks, providing a safer and more reliable cross-chain experience.

**Q3: What unique features does opZKP bring to the table？**

opZKP technology is characterized by its higher degree of decentralization. Compared to other Layer 2 solutions, it offers a secure and trustless solution. These features help improve Bitcoin’s scalability, efficiency, and overall security.

**Q4: How is high decentralization achieved?**

The zkBTC Cross-Chain Bridge achieves a high level of decentralization through measures such as deploying smart contracts on the Ethereum network,which are fully accessible for anyone to engage with and verify, and our open-sourced proof generator allows users to independently produce proofs. The team does not have access to private keys of any assets. These steps ensure transparency and security in operations, bolstering user trust.

**Q5: What is the Chainark tool, and what role does it play in the zkBTC Cross-Chain Bridge?**

Chainark is an open-source tool designed to prove recursive chain structures, which are crucial for diversified proof structures in the zkBTC Cross-Chain Bridge. It enables connection of the proof block to the genesis block through a single proof, regardless of the number of intermediate blocks, enhancing proof efficiency and system security.

#### **Q6:** Why did my redeem operation fail?

The redeem operation requires paying miner fees. If the current miner fee exceeds **5 times the estimated fluctuation range**, the operation will fail and return an error message indicating that the network fee is too high.

#### Q7: What happens if my deposit transaction includes multiple OP\_RETURN outputs?

The system **only recognizes the first OP\_RETURN output** in a transaction. It does not guarantee correct processing if there are multiple OP\_RETURN outputs. Please ensure that each deposit transaction contains only one OP\_RETURN output.

#### Q8: Is there a minimum asset requirement for redeem and deposit?

Yes. Both redeem and deposit operations require your zkBTC balance to be at least the **minimum amount (21000 sats)**.

#### Q9: What does "claim" and "store" mean in Feel Pool?

**Claim** allows you to receive zkBTC from the Fee Pool by depositing your $L2T tokens as proof of eligibility.\
When you perform a claim:

* You deposit a certain amount of $L2T to demonstrate your eligibility.
* In return, you will receive zkBTC from the Fee Pool proportional to your deposited $L2T amount.
* This process effectively converts your $L2T into zkBTC within the system, based on the current claim rate.

**Store** allows you to gain access to $L2T by locking up your zkBTC.\
When you perform a store:

* You deposit (store) your zkBTC into the system.
* In exchange, you will receive $L2T tokens, which can be used within the ecosystem.
* However, holding $L2T in this way incurs an **annual interest cost of 1.25%**, which is deducted from your $L2T balance over time as a storage fee.

#### **Q10:** Why did my cross-chain transaction fail?

Some wallets may shorten or omit bytes when building transactions. please make sure your wallet writes the **full 20-byte Ethereum address**, or the transaction will fail.

**Q11: What's opZKP upgrades? What's next?**

Bitcoin is due for an upgrade to enhance its network performance and address issues such as slow processing and high fees. opZKP is designed to enhance Bitcoin's scalability and transform it into a robust infrastructure. By implementing opZKP, Bitcoin could host a range of complex applications and smart contracts by then.&#x20;

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