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Introduction

The implementation of Verkle trees represents a significant advancement for the Ethereum network, offering a range of improvements that extend beyond merely reducing node operation costs. This article delves into the various benefits of Verkle trees, focusing on their impact on gas fees, node architecture, synchronization times, and decentralization.

A look at an over-simplified Ethereum roadmap. Source: Coinbase

What Are Verkle Trees?

Verkle trees are a more advanced data structure for state commitments in blockchain technology. These trees offer increased efficiency by reducing the size of proofs and lowering verification costs on-chain. Essentially, Merkle and Verkle trees are similar in structure but have distinct features that set them apart as data structures for state commitments.

In the Tendermint/Cosmos SDK structure, Merkle trees are utilized to share transaction data between nodes, specifically between full nodes and light nodes for the purpose of block verification. In this context, a light node receives a commitment from a full node and acquires a witness, allowing it to construct the root in the block header. In Ethereum, Merkle trees are utilized in the Execution layer, in which block headers consist of three roots of Merkle trees: the state root, the transaction root, and the receipt root. Additionally, Ethereum has a global state tree that updates over time, which increases in size as time goes on. This is one of the reasons why Ethereum is exploring the use of Verkle trees in future releases, as they can minimize the amount of state that full nodes are required to hold, which is referred to as statelessness (weak).

The primary difference between Verkle and Merkle trees is in how they organize their witnesses and, as a result, their sizes. In Verkle trees, instead of providing all the nodes that share a parent, you only need to provide the path to the root. This means that in a wide tree, the path will be much smaller compared to all the sister nodes that would have to be provided in a Merkle tree commitment. Another added commitment that is needed in Verkle trees is vector commitments, which replace the functionality of the sister nodes in Merkle trees. This means that they provide verification that a certain child node is the correct node in the tree while only providing the path itself. This eliminates the need for sister nodes in proof construction, making Verkle trees more efficient than Merkle trees.

Simple Verkle Tree Implementation. Source: Coffee and Rain

Verkle trees are instrumental in transitioning Ethereum clients towards a stateless design. In a stateless environment, clients can validate blocks without retaining the entire state database. Verkle trees facilitate this by generating compact witnesses, which are essentially smaller subsets of necessary state data, required for executing a transaction block, along with cryptographic proof confirming their authenticity. A witness in this context refers to a selection of specific state data needed to execute and validate a block's transactions. It serves as a testament to the accuracy and legitimacy of the transactions and the state alterations they cause. Witnesses are crucial in achieving statelessness for Ethereum clients. They enable these clients to verify block transactions without depending on a full, local copy of the state trie, a substantial data structure representing Ethereum's state.

The adoption of witnesses is key in enabling stateless clients to validate blocks with only the essential data, rather than maintaining a complete local copy of the state. This shift dramatically lowers storage demands for clients, contributing to a more lightweight and scalable system. However, the challenge lies in ensuring that these witnesses are sufficiently compact to be rapidly and efficiently transmitted across the network within the tight confines of a typical 12-second slot.

Verkle trees are adept at creating these small witnesses. They are a hybrid of "Vector commitment" and "Merkle Trees," hence the name "Verkle." Their design allows for efficient and secure data representation, paving the way for stateless clients that can validate blocks without a local state database. This advancement leads to better scalability, reduced storage needs, and increased overall network efficiency.

Verkle trees enable the creation of more compact witnesses compared to Merkle tries by optimizing data structure and representation. In a Merkle Trie, the witness must include the entire path from the leaf nodes (which hold specific state data) to the root hash, encompassing all intermediate hashes and sibling nodes needed for verification. This leads to a bulky witness size.

Conversely, Verkle trees simplify this path, effectively reducing the witness size. They organize data to minimize the required intermediate nodes for proving the inclusion of a leaf node in the tree and eliminate the necessity of including sibling nodes in the witness, streamlining the witness significantly.

Moreover, Verkle trees incorporate a potent polynomial commitment scheme, enhancing their space efficiency. This scheme ensures that the size of the witness remains constant, regardless of the number of leaves in the tree. The polynomial commitment offers a compact way to represent the witness data, facilitating its transmission across the peer-to-peer network.

This feature of Verkle trees is key to their efficiency and effectiveness in the Ethereum ecosystem. By providing a more space-efficient approach to representing state data, they enable faster and more streamlined block validation by stateless clients, contributing to the overall scalability and performance of the Ethereum network.

Increasing Mainnet Gas Capacity

One of the primary advantages of Verkle trees is their potential to substantially increase the mainnet gas capacity. This enhancement can facilitate a tenfold increase in gas limits, thereby improving transaction throughput and network efficiency. This is a crucial development for Ethereum as it continues to grow and scale.

Simplifying Node Architecture

Verkle trees also simplify the architecture of Ethereum nodes. By allowing the Execution Layer (EL) to function as a library rather than a fully-fledged node, the complexity of running and maintaining nodes is significantly reduced. This architectural shift can streamline node operations and maintenance, making it more accessible for users and developers alike.

Reducing Synchronization Time

Synchronization time is another critical factor in node operation. Verkle trees enable nodes to sync by downloading only the beacon state, which can drastically reduce synchronization times to mere seconds. This improvement is particularly beneficial for mobile and lightweight clients, making it feasible to run a node as part of wallet software even on mobile devices.

Enhancing Decentralization

Decentralization is a fundamental principle of blockchain technology, and Verkle trees contribute significantly to this goal. The cost of running a full node is a key parameter for decentralization. By reducing both the operational and hardware costs of node operation, Verkle trees make it more feasible for a broader range of participants to operate full nodes. This democratization of node operation enhances the network's resilience and security.

Enabling Full-Light Nodes

In the long term, Verkle trees pave the way for fully functional light nodes. These light nodes can be protected against invalid state transitions through simple fraud proofs for execution payloads. This feature is particularly valuable in scenarios where zero-knowledge proving does not fully protect the consensus and execution layers. By enabling efficient and secure light nodes, Verkle trees further support Ethereum's goal of robust and widespread decentralization.

Conclusion

The integration of Verkle trees into the Ethereum network offers numerous benefits, from increased gas capacity and simplified node architecture to reduced synchronization times and enhanced decentralization. As Ethereum continues to evolve, these improvements will play a crucial role in supporting its scalability, security, and accessibility. The adoption of Verkle trees marks a significant milestone in the ongoing development and optimization of the Ethereum blockchain.