EIP-7956: Tx Ordering via Block-Level Randomness

[aryaethn]

Hi,

@4rdii

In a system where validators select transactions but their ordering within a block is randomized to reduce MEV-driven front-running, how would your EIP address front-running strategies that operate across blocks or involve multiple transactions? For instance, consider a front-runner who identifies a victim’s high-value transaction (e.g., a large DeFi swap) in the mempool and proposes their own transaction one block earlier to manipulate the market state (e.g., inflating a token price before the victim’s swap).

As for your first question:

1. The attacker cannot make sure that he can have his transaction a block earlier than the victim’s transaction, unless he is the block builder.
2. Even if he can have his transaction one block earlier, his transaction can be easily back-run by other MEV extractors, since now his transaction is already in the block and every transaction will be in the next block. So, his transaction will have little to no benefit to front-run the victim, as he becomes the victim, himself.

@4rdii

Alternatively, what if the front-runner submits multiple redundant transactions (e.g., several swap transactions with slightly different parameters from different accounts) to increase the probability of a favorable random order within the victim’s block?

As for your second question:

The probability of getting a transaction before the victim’s k transactions is k/(k+1). If the attacker does craft transaction to be reverted, then he will fall for his own trap of making many transactions before the victim, and he will probably get back-run. Hence, I assume that he crafts the transactions to be reverted in case one is done.
In this case, the attacker must send base-fee and high priority-fee with each attacking transaction, to make sure they are included in the chain. This can lower their profitability significantly.

This means that the deterrent is economic, not cryptographic. The deterministic wins are removed, and what remains is costly lottery.