Ethereum is teeming with bots programmed to execute transactions in advance. The bots take advantage of the short window between when trades are submitted and when they are officially completed to copy other users’ trades, execute them quickly and eat away any profits.
It’s a practice called maximum extractable value (MEV), and it’s a huge pain for novice crypto traders and veterans alike.
But Ethereum’s transaction pipeline has undergone a quiet shift over the past two years, as more users of the chain have embraced “private mempools” to conduct their transactions — bypassing the blockchain’s “public” transaction lobby to prevent transactions from happening. be broadcast to the entire world before they’re finalized. This helps prevent MEV and helps users get better settlement of their transactions.
While there are clear benefits to this stealthy way of using Ethereum, experts say private mempools come with their own risks.
“I think almost everyone, including myself, expects to see more private transactions in the future, not fewer,” Matt Cutler, CEO of MEV company Blocknative, told CoinDesk. “I think the big question for me is: Would more private transactions be good or bad for the network?”
What is MEV?
To understand transactional privatization, you need to understand some of the quirks of how the second-largest blockchain network works today.
Submitting a transaction to Ethereum (and similar blockchains) typically means sending it to the chain’s ‘public’ mempool, which is a giant holding area for transactions still waiting to be executed.
The thousands of validators running Ethereum behind the scenes divide these mempool transactions into blocks – usually with the help of third-party “block builders” who organize them according to certain criteria, including how much they pay validators in fees. Once added to a block, the transactions are officially written to the blockchain, where they are permanently recorded.
This system poses an obvious problem: transactions in Ethereum’s public mempool are like sitting ducks. The seconds (or minutes) of queuing time leave enough for smart trading bots, known as ‘seekers’, to prepare trades or execute other strategies that eat into the profits of regular traders.
‘Private’ mempools are presented as a stealthier alternative, a way for decentralized finance (DeFi) traders to transact without exposing their trades to the prying eyes of MEV (maximum extractable value) bots. Those bots view mempool transactions to make a profit.
On average, about 10% of Ethereum transactions are routed through private mempools every day, which is double the share of private transactions the chain incorporated in 2022, according to Blocknative. Although the share of private transactions on Ethereum has fluctuated considerably in recent months (private transactions Although the economy peaked above 20% for a few days in 2023 before stabilizing closer to 10%, experts expect the trend toward mempool privatization to accelerate in the coming months.
Why go private?
The benefits of private mempools are clear.
Private mempool services from companies like CoW Swap, bloXroute, and Blocknative offer to hide transactions from MEV bots.
These settings are useful for large organizations and individuals who want higher security and privacy for their transactions. They are also used by sophisticated trading firms who want fast, guaranteed trade settlement and cannot afford to reveal their trades to competitors before they are filled.
Mempools aren’t just for big traders and privacy geeks, though.
Some private mempool services, such as CoWSwap, pay direct kickbacks (sometimes called “refunds”) to users whose transactions have the potential to earn block builders their own MEV profits.
There are also a growing number of products that use private mempools to ensure better settlement for DeFi traders. UniswapX, which is operated by Uniswap, the largest decentralized exchange on Ethereum, uses a kind of private mempool to help retail traders get better prices for their token swaps.
UniswapX’s private mempool connects traders directly to market makers, with the idea that this direct connection can give net traders better prices than they would on the open market.
What are the risks?
However, there are some risks.
Most pressing is the concern that private mempools could empower new intermediaries in key areas of Ethereum’s transaction pipeline: “I expect these will be centralizing in nature,” Cutler said.
MetaMask, the most popular Ethereum wallet, is ready to provide a transaction routing feature in 2024 that could catalyze the biggest shift yet away from Ethereum’s public mempool. But in a telling email exchange with CoinDesk when the feature was first reported, officials at Consensys, MetaMask’s parent company, pushed back against the “private mempool” label, which hints at some of the term’s baggage .
MetaMask’s new feature bypasses Ethereum’s public mempool – ostensibly as a way to help users transact more cheaply and with greater ease of use. MetaMask’s purpose-built sidetrack to the public Ethereum mempool is similar to the private mempool concept described in this article, but Consensys eschews the “private mempool” moniker because it comes with certain risks that MetaMask claims its technology does not have.
Read more: MetaMask’s secret project could turn the workings of Ethereum upside down
Private mempools often ask users to place their implicit trust in individual third parties, rather than the broader Ethereum network, to ensure their transactions are executed. Unless private mempools are carefully designed (and the details of the MetaMask system are not entirely clear), private mempools from these third parties may charge users or front-run them just like a normal MEV bot would doing.
Ethereum’s public transaction lobby has drawbacks, but it is also one of the main ways the network remains decentralized, and it provides users with clear insight into the status of their transactions.
Toni Wahrstätter, a researcher at the Ethereum Foundation, told CoinDesk via direct message on X that “the impact of private mempools on Ethereum’s network is a nuanced issue.”
On the plus side, Wharstätter noted that “more companies are now open sourcing their data,” meaning Ethereum’s research community has been able to perform more analysis on private mempool traffic.
Furthermore, “while they could lead to more centralization among builders and searchers, they are unlikely to affect the crucial aspect of validator decentralization,” Wharstätter added.
However, there are still some risks. “Looking ahead, I expect an increase in private order flow,” Wahrstätter continued. “It is important to monitor and address potential centralization issues among builders as this could threaten key features such as censorship resistance. If such centralization becomes significant, we will have to take steps to mitigate its impact.”
