BEVM: How to implement decentralized BTC layer2

Current mainstream BTC cross-chain bridge

1. WBTC: Centralized multisig custody 1:1 issued wrapped tokens on the Ethereum mainnet. $4.3 billion
2. tBTC: Distributed Threshold Signature 1:1 escrow BTC wrapped tokens issued on Ethereum. $50 million
3. L-BTC: BTC wrapped tokens issued by the Liquid sidechain 1:1. $80 million
4. Lightning Network: Tokens are locked in the mainnet, and off-chain bills do not require gas peer-to-peer payment transfers. $100 million

Two ideas for BTC fully decentralized Layer 2

1. Expand the OP Rollup model of the Lightning Network, not limited to payment, but can do arbitrary contract operations. BitVM is this line of thinking.
2. To decentralize the distributed threshold signature of tBTC on the chain, BEVM is this kind of thinking.

BEVM: Fully decentralized Bitcoin Layer 2 compatible with EVM

BEVM is a decentralized Bitcoin Layer 2 compatible with EVM ecology and uses native BTC as gas, BEVM introduces the EVM ecosystem into BTC, so that the Bitcoin ecosystem also has the ability to issue assets and build applications. It has the following technical characteristics:

1. EVM: Fully compatible with EVM ecology, wallets such as metamask, development frameworks such as truffle/hardhat, and solidity programming language.
2. BTC native gas: Use native BTC as the gas fee for EVM. Similar to ETH Layer2 OP/Starknet, ETH is used as the Gas fee for Layer 2.
3. Taproot Threshold Signature: On-chain POS nodes to ensure the decentralization of threshold signature verifiers. A single privacy communication protocol that ensures the security of aggregated Schnorr signed pubkey/msg.
4. Bitcoin light node: A light node on the BTC chain that supports the Wasm version (no_std).
5. Signal Privacy Distributed Protocol: The Signal protocol ensures the privacy and security of message communication between nodes when Schnorr aggregate signatures and Mast contract combination threshold signatures.
6. zkstark ultra-light node: For the optimization of the above light nodes, zkstark technology can be used to achieve ultra-light nodes of BTC.

The key to BEVM decentralized secure BTC layer2: **On-chain distributed threshold signature contract escrow, so that distributed threshold signature custodians can do 1000

1. Use Taproot (schnorr + mast contract) to generate a BTC mainnet threshold signing contract address (you can set the threshold threshold value of M/N, N can be selected to 1000 people, M/N generally takes 2/3)

2. Let the N participants of the BTC mainnet threshold contract address act as the POS verification nodes of BTC layer2, the N custodians of the BTC threshold contract and the POS verification node on Layer 2 completely coincide, and the security and decentralization of the entire BTC custody depend on the security and decentralization of the Layer2 POS network consensus.

3.L2/BEVM will fully implement a BTC on-chain light node, which can ensure that the data on the BTC chain can be synchronized to the BEVM network in real time. In other words: all nodes of BEVM have data from the BTC network.

4. BEVM’s POS network can achieve 1000 validators, and these 1000 validators are also co-custodians of BTC escrow contracts, only these 1000 validators greater than 2/3 of the verification nodes can operate after signing the consensus layer BTC and assets on the BTC network from L2 to L1. Assets crossing from BTC L1 to L2 only require users to transfer tokens or BTC to the threshold escrow address of these 1000 validators on the BTC network, and the assets on L2 will be automatically received on BTC Layer2 BEVM.

**Comparison of BEVM and other Layer2/cross-chain solutions. **

Although tBTC is already much more decentralized than wBTC, BEVM’s cross-chain model can also have the following advantages over tBTC’s threshold signature:**

1.### **No need to centralize initial setup. There is no need to use the shard private key to implement distributed threshold signature, which avoids the security problem of private key leakage caused by the shard private key. Directly use BTC’s native threshold signature scheme: MuSig2. ** 2.### ** Distributed network on the chain, more decentralized. The validators of the distributed threshold network are all block validators on the chain, and the network on the chain increases trust. It avoids the defects of opaque and easy operation of off-chain distributed networks. ** 3.### **No permission required, just trust the code. The BTC to Layer2 network uses BTC light nodes. The blockchain logic of fully trusting the code avoids the centralized fraud problem caused by the oracle submitting data to the off-chain distributed network. ** 4.### ** Distributed network communication, complete privacy. The Signal protocol is used to complete the communication problem of BTC primary root threshold signature. Solve the problem of private communication in distributed networks. Avoid the risk of data leakage, collusion, or external attacks when threshold signatures are present. **

BEVM compared to BitVM

BitVM is a computing paradigm for Turing-complete Bitcoin contracts launched by Robin Linus, head of ZeroSync, which, according to the white paper, is similar to OP Rollup on Ethereum. Instead of performing calculations on Bitcoin, contracts are validated without changing the role of network consensus.

BitVM’s OP Rollup’s execution VM has three major application promotion flaws.

• Limited to only two parties, and Defi basically requires three parties (the indispensable party is the on-chain contract escrow account address) to function properly.
• The mode of challenging the BTC mainnet off-chain between the two parties will be more complicated and difficult than the Lightning Network.
• It cannot be made into a mature general-purpose on-chain Layer 2 platform such as BEVM in a short period of time.