翻譯：白話區(qū)塊鏈

目前，比特幣第二層（L2）是這個(gè)問(wèn)題最有前景的答案。本文比較了比特幣L2與之前的努力，并討論了一些最有前景的比特幣L2項(xiàng)目。

1、保留無(wú)許可的比特幣

2、構(gòu)建比特幣產(chǎn)品

1）L1應(yīng)用程序

Ordinals 目前是在比特幣上使用銘文發(fā)行 NFT 和 BRC-20 代幣的標(biāo)準(zhǔn)。

2）比特虛擬機(jī)

BitVM 操作的簡(jiǎn)化圖解

3）側(cè)鏈

解決比特幣的有限初始化性的另一種方法是利用側(cè)鏈。側(cè)鏈?zhǔn)峭耆跏蓟莫?dú)立區(qū)塊鏈，例如與以太坊虛擬機(jī)（EVM）兼容，試圖與比特幣社區(qū)保持一致，并為該社區(qū)提供服務(wù)。Rootstock、Blockstream 的 Liquid 和 Stacks V1 是這些側(cè)鏈的示例。

比特幣側(cè)鏈已經(jīng)存在多年，通常在吸引比特幣用戶方面取得了有限的成功。例如，不到 4500 BTC 的流動(dòng)性被橋接到側(cè)鏈。然而，一些在這些鏈上構(gòu)建的 DeFi 應(yīng)用程序取得了一定的成功。例如，在 Rootstock 上的 Sovryn 和在 Stacks 上的 Alex。

比特幣 L2

比特幣 L2 正成為構(gòu)建基于 BTC 的無(wú)許可應(yīng)用程序的焦點(diǎn)。它們可以提供與側(cè)鏈相同的優(yōu)勢(shì)，但具有繼承比特幣基礎(chǔ)層的安全性保證。什么才是真正代表比特幣 L2 的持續(xù)性在本文中，我們避免了這種爭(zhēng)論，而是討論了如何使 L2 與 L1 聯(lián)系緊密，并討論了一些有前景的 L2 項(xiàng)目的主要考慮因素。

3、比特幣L2的要求

1）來(lái)自L1的安全性

比特幣L2最重要的要求是從L1的安全性中獲取其安全性。比特幣是最安全的鏈，用戶希望將安全性能延伸到L2。例如，閃電網(wǎng)絡(luò)已經(jīng)實(shí)現(xiàn)了這一點(diǎn)。

這就是為什么側(cè)鏈被澄清為側(cè)鏈的原因，它們有自己的安全性。例如，Stacks V1依賴于STX代幣來(lái)確保其安全性。

在實(shí)踐中，安全性要求很難實(shí)現(xiàn)。為了使 L1 安全地保護(hù) L2，L1 需要能夠執(zhí)行某些計(jì)算以驗(yàn)證 L2 的行為。例如，以太坊的滾動(dòng)從 L1 逐漸累積獲取其安全性，因?yàn)橐蕴?L1可以驗(yàn)證零知識(shí)證明（zk 滾動(dòng)漸變）或驗(yàn)證零知識(shí)證明（樂(lè)觀滾動(dòng)漸變）。比特幣基礎(chǔ)層目前缺乏支持這些操作的計(jì)算能力。建議在比特幣中添加新的操作碼，以允許基礎(chǔ)層驗(yàn)證通過(guò)限制連續(xù)提交的 ZKP。此外，諸如 BitVM 等提議試圖實(shí)現(xiàn)在針對(duì) L1 進(jìn)行更改的情況下實(shí)施欺詐證明的方式。BitVM 的挑戰(zhàn)導(dǎo)致欺詐證明的成本可能非常高（數(shù)百個(gè) L1 交易），從而了其實(shí)際應(yīng)用。

實(shí)現(xiàn)L1級(jí)別安全性的另一個(gè)要求是讓L1具有L2交易的不可變記錄。這被稱為數(shù)據(jù)可用性（DA）要求。它允許僅監(jiān)視L1鏈的觀察者驗(yàn)證L2狀態(tài)。通過(guò)銘文，可以將L2 TXs 的記錄嵌入比特幣 L1。然而，這引發(fā)了另一個(gè)問(wèn)題，可以擴(kuò)展性。比特幣 L1 每 10 分鐘 4MB 的塊時(shí)間限制，數(shù)據(jù)吞吐量有限，大約大約 ~ 1.1 KB/s即使將 L2 交易高度壓縮到約 10 字節(jié)/交易，假設(shè)所有 L1 交易都用于存儲(chǔ) L2 數(shù)據(jù)，L1 也只能支持約每秒 ~ 100 個(gè)交易的組合 L2 吞吐量。

2）從L1實(shí)現(xiàn)最小信任橋接

在以太坊的L2上，與L2的橋接由L1控制。橋接收L2，即轉(zhuǎn)入，實(shí)際上意味著在L1上鎖定資產(chǎn)，并在L2上鑄造該資產(chǎn)的復(fù)制品。在以太坊中，這是通過(guò)L2本地橋接智能合約實(shí)現(xiàn)的。該智能合約存儲(chǔ)所有橋接收L2的資產(chǎn)。智能合約的安全性來(lái)源于L1驗(yàn)證者。這使得橋接收L2的過(guò)程安全且最小化信任。

In Bitcoin, it is impossible to have a bridge that is collectively guaranteed by the entire L1 miners. Instead, the best option is to use a multi-signature wallet to store L2 assets. Therefore, the security of an L2 bridge depends on multi-signature security, i.e. the number of signers, their identities and how Peg-in and Peg-out operations are protected. One way to improve L2 bridge security is to use multiple multisigs instead of a single multisig that holds all L2 bridge assets. These include TBTC, where multisig signers must post collateral that can be slashed if they cheat. Likewise, the proposed BitVM bridge requires security deposits from multisig signers. However, in this multisig, any signer can initiate a Peg-out transaction. Peg-out interactions are protected by BitVM fraud proofs. If a signer behaves maliciously, other signers (verifiers) can submit fraud proofs on L1, resulting in slashing of the malicious signer.

4. Bitcoin L2 pattern

5. Main comparisons of Bitcoin L2 projects

1）Chainway

Chainway is building a zk rollup based on Bitcoin. Chainway rollup uses Bitcoin L1 as the data availability layer to store the rollup’s ZKP (zero-knowledge proof) and state differences. Additionally, this rollup exploits proof recursion so that each new proof aggregates the proofs issued on the previous L1 block. The proof also aggregates "forced transactions", which are L2-related transactions that force their inclusion on L2 by broadcasting on L1. This design has several advantages:

- By forcing transactions, ensures that Rollup's order generator cannot censor L2 transactions while giving users the right to include them by broadcasting them on L1.

- Using proofs recursively means that the prover of each block must verify the previous proof. This creates a chain of trust and guarantees that invalid proofs cannot be included on L1.

-The Chainway team also discussed using BitVM to ensure correct execution of proof verification and bridge transactions (peg-in/out). Using BitVM to verify bridged transactions reduces the trust assumption for bridged multisig to only an honest few.

2）Botanix

Botanix is ??building an EVM L2 for Bitcoin. To improve consistency with Bitcoin, Botanix L2 uses Bitcoin as a PoS asset to achieve consensus. L2 validators receive fees from transactions executed on L2. Additionally, L2 stores the Merkle root of all L2 transactions on L1 using inscriptions. This provides partial security for L2 transactions, as the L2 transaction log cannot be changed, but data availability for these transactions is not guaranteed.

Botanix is ??bridged from L1 via network processing on a decentralized multi-signature system called Spiderchain. Signers of a multi-signature are randomly selected from a set of arrangers. The orchestrator locks user funds on L1 and signs a statement to mint the corresponding amount of BTC on L2. Orchestrators are required to submit a security deposit to assume this role. Security deposits can be reduced in the event of malicious behavior.

Botanix has launched a public testnet, with the mainnet scheduled to launch in the first half of 2024.

3）Bison Network

Bison implements its Bitcoin L2 using a sovereign rollup style. It uses STARKs technology to implement zk rollup, and stores L2 transaction data and generated ZKP on L1 through Ordinals. Since Bitcoin cannot verify these proofs on L1, verification is delegated to users to verify ZKP on their devices.

For BTC bridging to/from L2, Bison uses Discreet Log contracts (DLC). Although the DLC is protected by L1, it relies on an external Oracle. This oracle reads the L2 state and passes the information to Bitcoin L1. If this oracle is centralized, it could maliciously spend assets locked on L1. Therefore, it is very important that Bison eventually plans to move to a decentralized DLC Oracle.

Bison also plans to support Rust-based zkVM. Currently, Bison OS implements many smart contracts, such as Token contracts, which can be verified using Bison prover.

4）Stacks V2

Stacks is one of the first projects focused on extending Bitcoin’s programmability. Stacks is being remodeled to better align with Bitcoin L1. This article focuses on the upcoming launch of Stacks V2 on the mainnet in April 2024. Stacks V2 implements two new concepts to improve alignment with L1. The first is the Nakamoto release, which updates the Stacks consensus to follow Bitcoin blocks and finality. The second is an improved BTC bridge called sBTC.

In Nakamoto’s release, blocks in Stacks were mined by miners who posted BTC collateral on L1. When Stacks miners create a block, these blocks will be pegged to Bitcoin L1 and receive confirmations from L1 PoW miners. When a block receives 150 L1 confirmations, the block is considered final and cannot be forked without forking Bitcoin L1. At this point, the Stacks miner who mined the block will be rewarded with STX and have their BTC collateral distributed to Stackers in the network. This way, any Stacks block older than 150 blocks (~1 day) relies on Bitcoin L1 security. For newer blocks ( 150 confirmations), the Stacks chain can only fork if 70% of Stackers support the fork.

Another Stacks upgrade is sBTC, which provides a more secure way to bridge BTC to Stacks. To bridge assets to Stacks, users deposit their BTC into an L1 address controlled by L2 Stackers. When the deposit transaction is confirmed, sBTC will be minted on L2. To ensure the security of bridged BTC, Stackers must lock up a deposit in STX that exceeds the value of the bridged BTC. Stackers are also responsible for executing peg-out requests from L2. Peg-out requests are broadcast as L1 transactions. Upon confirmation, Stackers burn sBTC on L2 and collaborate to sign an L1 transaction that releases the user’s BTC on L1. For this work, Stackers are rewarded with the previously discussed miner deposit. This mechanism is called Proof of Transfer (PoX).

Stacks aligns with Bitcoin by requiring that many important L2 transactions, such as miner PoX deposits, Peg-out transactions, etc., are performed on L1. This requirement does improve the alignment and security of bridging BTC, but may result in a degraded user experience due to L1’s volatility and high fees. Overall, the updated Stacks design resolves many of the issues in V1, but there are still some weaknesses. This includes the use of STX as a native asset in L2 as well as L2 data availability where only hashes of transaction and smart contract code are available on L1.

5）BOB

BOB（Build-on-Bitcoin）是一個(gè)旨在與比特幣瞄準(zhǔn)的以太坊L2。BOB在以太坊上作為一個(gè)樂(lè)觀的滾動(dòng)Rollup運(yùn)行，并使用EVM執(zhí)行環(huán)境來(lái)實(shí)現(xiàn)智能合約。

BOB初步接受不同類型的橋接BTC（WBTC、TBTC V2），但計(jì)劃未來(lái)采用更安全的實(shí)體橋接，使用BitVM。

BOB的當(dāng)前設(shè)計(jì)更好地描述為一條側(cè)鏈，而不是比特幣L2。這主要是因?yàn)锽OB的安全性依賴于以太坊L1，而不是比特幣的安全性。

6）SatoshiVM

其匿名性，該項(xiàng)目引發(fā)了很多爭(zhēng)議。一些調(diào)查顯示該項(xiàng)目與 Bool Network 有聯(lián)系，目前是一個(gè)較早的比特幣 L2 項(xiàng)目。

6、比特幣L2范式中的創(chuàng)業(yè)機(jī)會(huì)

比特幣 L2 領(lǐng)域提供了一些創(chuàng)業(yè)機(jī)會(huì)。除了構(gòu)建最佳的比特幣 L2 的環(huán)球的機(jī)會(huì)之外，還有其他一些創(chuàng)業(yè)機(jī)會(huì)。

1）比特幣數(shù)據(jù)可用性層

2）MEV提取

3）比特幣收益工具

7、總結(jié)

熱點(diǎn)：比特幣 特幣 LAYER 項(xiàng)目