The BVM (Bitcoin Virtual Machine) Layer 3 is a solution that introduces a virtual machine to the Bitcoin network, enabling the execution of smart contracts and decentralized applications (dApps) with greater flexibility and computing power than what is currently possible on the original Bitcoin network (Layer 1) and its Layer 2 scalability solutions such as the Lightning Network. There are already several Layer2 on Bitcoin: Lightning Network (uses bidirectional payment channels between two parties, off chain), Stacks (for dapps and smart contracts mainly), without forgetting Rootstock or BEVM (BTC sidechains compatible with the EVM world --> Metamask ) or privacy-focused solutions like Liquid Network. However, Layer3 solutions are also starting to spread, for example ZK Bitcoin (update for BVM V2). We have already seen Layer3 on Arbitrum (Xai), Optimism (Op Stack), Zksync (Hyperchains), Base (Degen Chain) or the rollups on Dymension.
L3 are virtual machines similar to structures such as AWS (Amazon Web Service), Digital Oceans or Google Cloud. What is the difference? These clouds are centralized. L3s on Bitcoin are based on the Supersonic architecture, a special ZK-rollup Bitcoin L2 based on the BVM ZK-Rollup module. Its sole purpose is to power thousands of Bitcoin L3 ZK-rollups. These L3s are rollups connected to Supersonic.
The steps to perform a ZK rollup from Bitcoin L3 to Supersonic (Bitcoin L2) are as follows:
1) A user sends a transaction to the Bitcoin L3 Sequencer which executes the transaction and provides a confirmation
2) The Bitcoin L3 Sequencer can include the transaction in the block if the user decides to do it
3) L3 Sequencer executes the block of transactions and sends it to the Bitcoin L3 Prover
4) Bitcoin L3 Prover creates a cryptographic proof of block execution and sends it to the smart contract on Supersonic
5) The smart contract verifies that the proof is valid and that all data has been sent, then updates the rollup status in the contract
6) L3 Sequencer sends the block data to one of the data availabilities supported by BVM (Avail, Celestia, Polygon, etc)
The steps to perform a ZK rollup from Supersonic (Bitcoin L2) to Bitcoin (L1) are as follows:
1) A Bitcoin L3 Sequencer "wraps" around the Supersonic Sequencer
2) The Supersonic Sequencer executes the block of transactions and sends it to the Supersonic Prover who creates a cryptographic proof of the block execution along with a "commitment" and writes them into Bitcoin as Ordinals
3) The Supersonic Sequencer sends the block data to one of the data availabilities supported by BVM
4) The Supersonic Light Node verifies that the commitment and proof are valid and that all data has been sent, then updates the rollup status in the local data
VERIFICATION LOGIC
Supersonic Light Nodes can be run by anyone to ensure correct execution in Bitcoin L3 and Supersonic. In particular, Light Nodes validate Bitcoin L3 sequencer transactions and verify that those performed on Bitcoin by the supersonic sequencer are accurate.
Supersonic nodes are especially useful for decentralized bridges that need to verify the validity of states committed to Bitcoin before processing withdrawal transactions.
Initially, Supersonic Light Nodes are run server-side or on a local computer. In the future, according to the team, it will be possible to create a Supersonic Light Node mobile app to allow anyone to quickly perform a verification. The verification process is quite similar to Bitcoin L3 verification. The only difference is that the Supersonic commitment and zk-proofs are extracted directly from Bitcoin instead of from data availabilities.
GREATER EFFICIENCY AND SCALABILITY
In BVM V1, the cost of L2 fees was primarily derived from the cost of Bitcoin rollups. As the number of L2s increased, the overall cost of fees also increased. In BVM V2, since the size of the zk-proof is constant, the size of the data written to Bitcoin is also constant. This means that the cost of rolling up in Bitcoin remains constant, resulting in lower costs per L2 as more are added.
As for transaction times they are obviously faster: 1 second block times compared to the 2 second block time in BVM V1. This Layer3 represents a step forward for the Bitcoin network, expanding its sectors and uses. Although still in the conceptual and development phase, the Bitcoin Virtual Machine could revolutionize the Bitcoin ecosystem by introducing advanced smart contract features and increasing the interoperability and scalability of the network.
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