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Ethereum Study - RLP to SSZ MPT commitment migration

The Ethereum Foundation commissioned our team to examine the potential impact of Ethereum Improvement Proposals (EIPs) 6404 and 6466. These EIPs propose the modification of Merkle-Patricia Trie (MPT) commitments for transactions and receipts, respectively. Importantly, this entails a change in the serialization algorithm, from Recursive Length Prefix (RLP) format to the Simple Serialize (SSZ) format for the Receipts and Transactions containers. In turn, this changes the Receipts Root and Transactions Root fields in the execution layer headers.

A primary concern is that this transition could disrupt contracts that rely on RLP for proofs on data committed to the Ethereum mainnet. These contracts may include critical parts of decentralized bridges, which generate proofs about some log that was emitted in historical transactions.

This research seeks to quantify and qualify the extent of potential disruption caused by these changes. Identifying the specific on-chain patterns that verify commitments in this manner represents a significant challenge, necessitating a semi-automated examination of all smart contracts deployed on the Ethereum network, together with their recent behavior. The study also attempts to identify which projects these contracts are part of, and whether actions can be taken, on-chain (such as upgrading) or off-chain (such as modifying their respective oracles) to limit the impact of these changes.

For the proposed EIPs, we were able to measure the extent of the impact of these changes. The effects are observed on a handful of known projects, all of which are cross-chain bridges.

Notably, many other protocols that do employ RLP functionality are not affected. For instance the Optimism and Polygon bridges use RLP operations for inclusion proofs when bridging from L2 networks back to Ethereum, and, thus, are not affected by the Ethereum encoding of transactions.

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Finally, an interesting result of our study is that out of the two proposed EIPs, only EIP-6466 (Receipts Root EIP) was observed to have an impact on the inspected protocols. This makes sense as log-inclusion proofs are probably the most common way to conduct cross-chain message passing.
Read the rest of the study here.