By Bitcoin Revista - fa 3 mesos - Temps de lectura: 11 minuts
Valor extraïble del miner (MEV) i diners programables: el bo, el dolent i el lleig
El nucli de Bitcoin’s security model relies on this basic game theory—miners, armed with their digital pickaxes, are in a relentless chase for profit. And it’s this pursuit that keeps the network secure. Basic vanilla mining involves producing blocks to earn the block rewards and transaction fees, but have you ever considered that miners might have other ways to extract value from the blockchain beyond this standard mining process? Are there other avenues for profit on the blockchain where miners can leverage their unique position as validators?
Què és MEV?
En els sistemes de prova de treball, "Valor extraïble del miner"(MRS) és un terme que descriu els beneficis que poden obtenir els miners manipulant com es prioritzen, s'exclouen, es reorganitzen o es modifiquen les transaccions als blocs que mine. Tanmateix, des de l'actualització d'Ethereum a Ethereum 2.0, que va traslladar la xarxa a la prova de participació, el concepte de MEV ha agafat un nou nom i ara es coneix com a "Valor màxim d'extracció" als sistemes de prova de participació. En aquest context, són els proposants de blocs en lloc dels miners, que són els validadors, els que tenen l'oportunitat d'extreure aquest valor.
Els miners (o validadors a Ethereum) tenen un paper especial en aquestes xarxes confirmant transaccions en blocs. La seva posició els situa un pas per davant dels altres usuaris i els permet determinar el ordre final de les transaccions a la cadena. Dins d'un bloc, les transaccions normalment s'ordenen amb les tarifes més altes a la part superior, però de tant en tant s'obren oportunitats que permetrien als miners prendre una benefici addicional canviant estratègicament l'ordre de les transaccions en benefici propi.
Podríeu pensar, quin és el mal de deixar que els miners treguin una mica de beneficis addicionals? Les preocupacions només comencen a sorgir quan alguns d'aquests miners, els equipats amb capacitats analítiques més avançades i una informàtica més potent, poden identificar i explotar les oportunitats de beneficis MEV amb més eficàcia que altres.
These opportunities might not always be easy to spot, but the more value that can be extracted through analyzing the chain, the stronger the incentive becomes for research teams equipped with bots to do this work. Over time, this disparity in miner's profit-making ability creates a trend toward centralization within the network. Ultimately undermining the core principle of the blockchain: decentralization.
This is exactly the scenario the Bitcoin developer community is aiming to prevent when considering how best to manage more expressivity on Bitcoin.
Per què volem diners programables?
Històricament, Bitcoin has operated with relatively simple smart contracts. However, this model struggles with even moderately complex transactions. Bitcoin Script can only validate authentication data, it doesn’t have the capability to impose speed limits on transactions or define coin destinations because Bitcoin Script doesn’t have access to transaction data.
As a somewhat separate issue, working with and writing Bitcoin smart contracts can be challenging for users who don't fully grasp its security requirements. A proposed feature, known as ‘vaults,’ aims to solve some of these pain points by introducing time-locked conditions for transactions. Essentially, vaults could serve as an emergency “escape hatch,” allowing users to recover their funds in the event of compromised private keys. But features like this are only possible with more expressivity.
Ethereum is widely recognized for its highly expressive scripting capabilities, but it also notably struggles with the issue of MEV. Most users generally assume that Bitcoin has no MEV, in stark contrast to Ethereum, which is viewed as a wild frontier for it. But is this the full story?
Els contractes intel·ligents més expressius incentiven automàticament més escenaris MEV?
Hi ha diversos factors que contribueixen al MEV: (1) transparència de mempool, (2) transparència del contracte intel·ligent i (3) expressivitat del contracte intel·ligent. Cadascun d'aquests factors obre nous canals per a MEV, els revisarem aquí.
El dolent: (1) Transparència de Mempool
like Bitcoin's mempool, the mempools of most blockchains are fully transparent, open, and visible, so that everyone can see what transactions are pending before being validated and confirmed in a block. Bitcoin blocks typically take about 10 minutes to find, which theoretically gives miners that same amount of time to take advantage and front-run.
In practice, on Bitcoin, this isn’t a source of MEV for a few reasons: (1) Bitcoin transactions are simple enough that no miners have a significant analytic advantage over other miners, and (2) Bitcoin transactions generally don’t execute multi-asset transactions such as swaps or open trades that could be front-run.
Compareu-ho amb Ethereum, que té algunes de les transaccions multiactius més complexes que tenen lloc en intercanvis públics descentralitzats (DEX). Oficialment, el temps de bloc a Ethereum és de 15 segons, però durant els períodes d'alt trànsit de mempool, les tarifes de gas necessàries per a la inclusió immediata del bloc poden superar fàcilment els cent dòlars. Com a resultat, les transaccions amb comissions més baixes acaben esperant minuts o fins i tot hores abans d'incloure's en un bloc. Això pot allargar la finestra per a aquestes nefastes oportunitats d'avantguarda, que ja són més freqüents a Ethereum a causa del valor substancial embolicat en fitxes de capa 2.
El dolent: (2) Transparència del contracte intel·ligent
In Bitcoin “smart contracts” are the simple locking and unlocking mechanism inherent in Bitcoin Script. The transaction values, sender, and receiver details are all publicly visible on the blockchain. While this complete and naked transparency isn’t ideal from a privacy perspective, it’s part of how Bitcoin allows all participants in the network to verify the full state of the blockchain. Any observer can analyze these contract details, potentially opening the door to certain MEV-related strategies.
Però el Bitcoin scripting language is, by design, quite limited, focusing primarily on the basic functions of sending and receiving funds, and validating transactions with signatures or hashlocks. This simplicity inherently limits the scope for MEV strategies on Bitcoin, making such opportunities relatively scarce compared to other chains.
Platforms like Ethereum, Solana, and Cardano also have fully transparent smart contracts, but they diverge from Bitcoin by also having highly complex and expressive scripting languages. Their Turing-complete systems make it possible to theoretically execute virtually any computational task which has come to include: self-executing contracts, integration of real-world data through oracles, decentralized applications (dApps), layer-2 tokens, swaps within DEXs, and automated market makers (AMMs). These come together to foster a rich environment for MEV opportunities. Zero-knowledge-proof-based schemes, such as STARKex, could theoretically avoid some of these issues, but this trade-off would come with other complexities.
The Ugly: (3) Expressivitat del contracte intel·ligent
The MEV opportunities are so lucrative on some chains that there are “MEV trading firms” bringing in “high five figures, mid six figures” in profits a month. This trend has become so prominent that there are public dashboards dedicated to scanning for profitable opportunities on Ethereum and Solana. Their profitability is generated by executing the full basket of MEV strategies: front-running, sandwich trading, token arbitrage, back-running, and liquidations to name a few. Each exploiting a different smart contract dynamics for profit.
Algunes d'aquestes estratègies MEV s'apliquen tant a la capa 1 com a la capa 2.
Generalized Front-Running: Bots scan the mempool for profitable transactions, and then front-run the original transaction for a profit.Sandwich Trading: The attacker places orders both before and after a large transaction to manipulate asset prices for profit. This strategy leverages the predictable price movement caused by the large transaction.Aleshores, certes estratègies són úniques per a fitxes de capa 2 i contractes intel·ligents.
Arbitrage Across Different DEXs: Bots exploit price differences for the same asset on various DEXs by buying low on one and selling high on another.Back-running in DeFi Bonding Curves: MEV bots capitalize on predictable price rises in DeFi bonding curves by placing transactions immediately after large ones, buying during uptrends, and selling for profit. DeFi Liquidations: MEV bots spot opportunities in DeFi lending where collateral values fall below set thresholds, allowing validator's to prioritize their transactions for buying the liquidated collateral at lower prices.La complexitat dels contractes contribueix significativament als reptes associats al MEV.
Re-entrancy Attacks: These attacks exploit smart contract logic flaws, allowing attackers to repeatedly call a function before the first execution completes, extracting funds multiple times. In the context of MEV, skilled individuals can significantly profit from this, particularly in contracts with substantial funds.Interconnected Contracts and Global State: On platforms like Ethereum, smart contracts can interact, leading to chain reactions across several contracts from a single transaction. This interconnectivity enables complex MEV strategies, where a transaction in one contract may impact another, offering a chain reaction of profit opportunities.Una part del problema aquí és que el valor total creat per fitxes i dApps construïts a la capa 2 sovint supera el valor de l'actiu natiu de la cadena de blocs a la capa 1, soscavant l'incentiu dels validadors per seleccionar i confirmar transaccions basades exclusivament en tarifes.
Per empitjorar les coses, moltes d'aquestes oportunitats no es limiten estrictament als validadors de xarxa. Altres participants de la xarxa amb robots d'escaneig MEV poden competir per aquestes mateixes oportunitats, provocant congestió de la xarxa, augmentant les tarifes del gas i augmentant els costos de transacció. Aquest escenari crea una externalitat negativa per a la xarxa i els seus usuaris, que es veuen afectats pel preu de les comissions de transacció més altes, ja que la cadena es torna menys eficient i més cara d'operar. El MEV a DeFi és tan comú que els usuaris gairebé l'han acceptat com un impost invisible per a tothom a la xarxa.
Aquestes oportunitats de MEV sorgeixen naturalment com un subproducte dels contractes intel·ligents altament expressius, o hi ha una ruta alternativa al somni de diners totalment programables?
Short of avoiding protocols with highly expressive smart contracts and layer-2 tokens, users can avoid some of these risks by utilizing protocols that support Transaccions confidencials, like Liquid, that conceal transaction details. But unlike these platforms with more expressive scripting languages, Bitcoin lacks the ability to do things you would expect to be able to do with programmable money.
El bo: intercanvis amb diners programables
When considering the evolution of smart contracts on Bitcoin the options we’re given are to (1) push the complexity off-chain, (2) cautiously integrate narrow or limited covenant functionalities, or (3) embrace the path of full expressivity. Let’s explore some of the proposals from each of these options.
(1) Una nova estructura per als contractes fora de la cadena: QUALSEVOL PREV
Off-chain solutions, like the Lightning Network, aim to enhance Bitcoin’s scalability and functionality without burdening the mainchain, keeping transactions fast and fees low. This all sounds good so far.
SIGHASH_ANYPREVOUT (APO) és una proposta per a un nou tipus de clau pública que permet certs ajustos a una transacció fins i tot després de signar-la. Simplifica com s'actualitzen les transaccions, permetent que les transaccions es refereixin a anteriors (UTXO) amb més facilitat, fent que els canals de Lightning Network siguin més ràpids, més barats, més segurs i més senzills, especialment en la resolució de disputes.
Under the hood, APO is a new proposed type of sighash flag. Every Bitcoin transaction must have a signature to prove it’s legitimate. When creating this signature, you use a “sighash flag” to determine which parts of the transaction you’re signing. With APO a sender would sign all outputs and none of the inputs, to commit the outputs of the transaction, but not specifically which transaction the funds are going to come from.
APO enables Eltoo, allowing users to exchange pre-signed transactions off-chain. However APO may inadvertently introduce MEV by making transactions reorderable. As soon as you allow a signature that’s binding the transaction graph you have the ability to swap out transactions. Inputs can be swapped, as long as the new inputs are still compatible with the signature.
(2) Pactes: CAT + CSFS i CTV
Els pactes permetrien als usuaris controlar on es poden moure les monedes, imposant límits de velocitat o establint destinacions específiques per a les monedes en una transacció. Hi ha dues categories diferents de pactes: recursius i no recursius.
Recursive covenants allow coins to continually return to covenants of the same type.Non-recursive covenants limit this control to the next transaction, requiring the entire future path of the coins to be defined upfront.CAT + CSFS is a covenant proposal that allows scripts to construct or define certain parts of a future transaction. CHECKSIGFROMSTACK (CSFS) verifies a signature against the data that OP_CAT constructed. By using CSFS to require the signature to match some dynamically constructed format from OP_CAT, we can define how these UTXOs can be spent in the future and create a recursive covenant, albeit clunkily.
OP_CHECKTEMPLATEVERIFY (CTV) és una manera de crear pactes no recursius. En lloc de definir i verificar amb parts específiques d'una transacció, CTV restringeix com es poden gastar els fons, sense especificar la següent adreça exacta a la qual han d'anar. Defineix una "plantilla" que la següent transacció ha de confirmar.
One risk with recursive covenants might be possible to create a scenario where coins must follow a set of rules that repeat over and over, that get trapped in a loop without a way of getting out. Another is that, because covenants are transparent and self-executing they could open Bitcoin up to some of the MEV strategies we see on other chains.
Quina és la bona notícia aquí?
La bona notícia és que totes aquestes propostes introdueixen una nova expressivitat!
Ara quina és la màxima expressivitat que podem obtenir?
(3) Expressivitat plena: senzillesa
Senzillesa is a blockchain-based programming language that differs from other scripting languages in that it is very low-level. It is not a language on top of Bitcoin Script or a new opcode within it, it’s an alternative to it. Theoretically, it’s possible to implement all covenant proposals within Simplicity, and implement many of the other contracts cypherpunks want from programmable money, but with less of the negative externalities of Ethereum.
Simplicity maintains Bitcoin’s design principle of self-contained transactions whereby programs do not have access to any information outside the transaction. Designed for both maximal expressiveness and safety, Simplicity supports formal verification and static analysis, giving users more reliable smart contracts.
Compare Simplicity to: (1) bitcoin covenant proposals and (2) scripting languages on other blockchains:
The covenant proposals on Bitcoin Script, though much simpler than Simplicity, lack the expressivity to handle fee estimation in Script, due to Bitcoin's lack of arithmetic functions. There is no way to multiply or divide, no conditionals or stack manipulations opcodes; it is also very hard to estimate a reasonable fee to be associated with a given contract or covenant. Users end up with spaghetti code, where 80% of their contract logic is dedicated to trying to determine what their fee rate should be. Making these covenant contracts super complicated and difficult to reason about.
The EVM has looping constructs which makes static analysis of gas usage very difficult. Whereas with Script or Simplicity, you can just count each opcode, or recursively add up the cost of each function. Because Simplicity has a formal model, you can formally reason about program behavior. You can't do this with Script even though you can do static analysis of resource usage.
La senzillesa proporcionaria als usuaris el grau més alt d'expressivitat, juntament amb altres funcions valuoses com l'anàlisi estàtica i la verificació formal. Els usuaris estan incentivats, encara que no estan restringits, a crear contractes intel·ligents que siguin resistents a MEV. A més, una combinació de diferents contractes junts pot donar lloc a MEV, fins i tot quan individualment no ho fan. Això representa una compensació fonamental.
The idea of advancing Bitcoin’s smart contract functionality is undeniably promising and exciting. But it’s important to acknowledge that all these proposals carry some degree of MEV risk—albeit likely not to the extent that we see on other chains. As we think about bringing more programmable money to Bitcoin, there are questions we have to ask:
Can we build a protocol with zero MEV risk, or is this an unattainable ideal?Given the inherent risks of MEV in many proposals, what level of MEV risk is acceptable?And finally, what represents the simplest proposal that offers the greatest degree of expressivity?Cada proposta té el seu propi conjunt d'avantatges i inconvenients. No obstant això, independentment de la direcció que prenguem, sempre hauríem de tenir com a objectiu prioritzar la seguretat i mantenir el principi de descentralització.
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This is a guest post by Kiara Bickers. Opinions expressed are entirely their own and do not necessarily reflect those of BTC Inc or Bitcoin Revista.
Font original: Bitcoin Magazine