# How Open Ethereum Counters Sandwich Attacks: FOCIL and Crypto-Mempool Change the Game

Vitalik Buterin has been contemplating Ethereum’s future not just as a financial network but as a tool that must operate independently of pressure from governments, corporations, and other external factors. Along this path, the founder of Ethereum faced a paradox: the more the protocol specializes at the block creation level, the greater the risk of losing its main value—openness. That’s why today’s discussions focus on two technologies: FOCIL (Forced Inclusion Lists) and cryptographic mempools, which aim to restore Ethereum’s resistance to censorship and sandwich attacks.

Vitalik Redefines Ethereum’s Mission: From Finance to Sanctuary Technology

In early March 2026, Vitalik Buterin proposed a new framework for understanding Ethereum’s role in the world. He called it “sanctuary technologies”—open tools that enable people to live, work, collaborate, and accumulate wealth while maintaining maximum resilience against external pressures.

This is not just a rebranding. Vitalik acknowledged that despite ecosystem development, Ethereum has yet to change most people’s daily lives. Instead of grand promises to “change the world,” he offers a more modest but powerful idea: envision Ethereum as part of a broader system of tools that work like a hammer—you buy it, and it becomes yours forever. It won’t stop working if the manufacturer goes bankrupt, nor will it display messages like “this feature is unavailable in your region.”

This definition of “sanctuary technologies” means Ethereum must pass one of the strictest tests in cryptography—the Walkaway Test. The simple question: will the protocol continue to function if all key developers disappear tomorrow? This is not rhetoric but a high-level engineering challenge.

Open Mempool as a Bottleneck: Why Sandwich Attacks Are No Longer Just Theory

In practice, the open Ethereum network has faced increasing specialization at the block-building level. Previously, each validator created blocks locally—ideal for distribution. Now, this role has been handed to a small number of powerful builders who optimize for extracting MEV (Maximum Extractable Value).

The problem is that when the right to build blocks concentrates, the open transaction pool (mempool) becomes vulnerable. Any builder can see all incoming transactions in real time and use this information to:

• Front-run: send their transaction ahead of a user’s transaction
• Sandwich attack: “sandwich” the user’s transaction between two of their own
• Reorder: change execution order for advantage

For the average user, this means their transaction can be compromised even before it enters a block. A DeFi user might send a swap, but a builder seeing this intent could perform their swap first, drastically changing the price, and then allow the user to complete the trade under unfavorable conditions.

It’s not just about transaction costs or network throughput. It’s about whether open infrastructure can truly protect users from manipulation.

FOCIL: How Forced Inclusion Lists Restore Control to Open Ethereum

FOCIL (Fork-Choice Enforced Inclusion Lists) is a protocol response to censorship and manipulation issues in open mempools. The mechanism works as follows:

In each slot (time window), a committee of validators is selected to form a list of transactions that must be included based on mempool observations. This list is broadcast to the network. The proposer for the next slot must build a block adhering to these constraints. Attesters (voters) approve only blocks that satisfy the inclusion list.

Key feature: FOCIL does not eliminate builders. They can still optimize transaction order and extract MEV, but they lose the right to decide which legitimate transactions will be included in the block. Thus, the open mempool regains a guarantee: if your transaction is valid, it will be included.

FOCIL is already part of the main proposals for the consensus layer update called Hegotá, scheduled for the second half of 2026 after the Glamsterdam upgrade. This indicates that the solution is in the final stages (Specification Freeze Included).

Crypto Mempool and LUCID: Encryption as a Solution to Front-Running

However, FOCIL only addresses part of the problem. It guarantees inclusion but does not hide transaction content. Sandwich attacks can still occur if MEV searchers and builders see deal details before execution.

This is where cryptographic mempools come into play—another part of the solution. The core idea:

• Users send encrypted transactions
• The transaction remains encrypted in the mempool and while in the open pool
• Decryption occurs only after inclusion in a block and reaching a certain number of confirmations (finalization)
• Until then, no one can see the user’s intentions, fully preventing front-running and sandwich attacks

Currently, the community is discussing two main proposals: LUCID (by Ethereum Foundation researchers Andres Elovsson, Julian Ma, and Justin Florentine) and EIP-8105 (a universal encrypted mempool). Notably, the EIP-8105 team recently announced full support for LUCID, and both groups are working toward a unified solution.

Together, these mechanisms form what researchers call the “Holy Trinity of Censorship Resistance”:

• ePBS (separating proposer and builder at execution level)
• FOCIL (guaranteed inclusion of open transactions)
• Cryptographic Mempool (hiding intentions until finalization)

From Theory to Practice: Why This Matters for Open Ethereum

At first glance, these changes may seem to add complexity to the protocol. Developers debate whether the added complexity and potential efficiency loss justify implementing FOCIL and encrypted mempools.

But the essence of “sanctuary technologies” lies here: the true value of blockchain isn’t just in holding assets or speeding up payments. It’s in whether the technology can provide people with a digital exit—an uncensorable, hard-to-disable, and impossible-to-freeze means of living, working, and accumulating wealth—even under pressure.

When open Ethereum guarantees that valid transactions will be included, cannot be blocked by a small group, and that intentions are protected by encryption until execution—only then does the protocol truly pass the Walkaway Test.

This means Ethereum must operate not based on the goodwill of operators or market equilibrium but through strict protocol rules. When millions of users can freely live, work, communicate, and build wealth on open Ethereum without fear of arbitrary censorship or confiscation—that’s when the goal is achieved.

FOCIL and cryptographic mempools are not just technical innovations for another upgrade. They are a redefinition of Ethereum’s very philosophy: from a network that hopes to remain open to a network that guarantees its openness through code.