MHOT: Height-Optimized Authenticated Data Structure for Blockchain State Commitment

2026-06-10

AI Summary

This work addresses critical performance and security limitations of the Merkle Patricia Trie (MPT) in blockchain state commitments, where increasing tree height induces bottlenecks and renders the structure vulnerable to low-cost Nurgle attacks with up to 99.97% success rates. To overcome these issues, the authors propose MHOT, a novel authenticated data structure that explicitly optimizes tree height as a first-class abstraction. MHOT decouples fanout from span through an adaptive, discriminative-bit-based indexing scheme, achieving linear coupling and minimizing tree height. It further introduces a two-layer Merkle hierarchical proof mechanism that drastically reduces verification overhead using only standard cryptographic hashes and without requiring a trusted setup. Experimental evaluation under Ethereum mainnet workloads demonstrates that MHOT achieves 9× higher write throughput, 4× lower write amplification, 2× smaller proof sizes, and complete immunity to Nurgle attacks.

Abstract

State root computation dominates (78%) blockchain block processing time. Ethereum's canonical authenticated data structure, i.e., Merkle Patricia Trie (MPT), suffers from severe tree-height growth and is vulnerable to \textit{Nurgle attacks} (SP'24), where adversaries inflate path depth via hash collisions and degrade system performance at negligible cost. Existing defenses increase node fanout (span) to bound tree height, but higher span inflates proof size exponentially. Prior work mitigates this trade-off using vector commitments, at the cost of trusted setup or expensive verification. We present \textsc{Mhot}, a height-optimal authenticated data structure for blockchain state commitment that preserves standard hash-based verification without trusted setup. Unlike MPT's fixed-prefix indexing, which couples span and fanout exponentially, \textsc{Mhot} indexes by discriminative bits that actually distinguish keys, achieving adaptive span with linear fanout coupling and provably minimal height. To prevent high fanout from inflating proofs, we introduce hierarchical proofs, a two-layer Merkle construction that reduces per-node proof overhead from O(k) to O(log k). On Ethereum mainnet workloads, \textsc{Mhot} achieves up to 9X higher write throughput, 4X lower write amplification, and 2X smaller proofs than MPT. Under Nurgle attacks, even when the adversary consumes an entire block's gas budget, \textsc{Mhot} maintains a 0% attack success rate (v.s., 99.97% for MPT). Our results, somewhat surprisingly, show that height optimality (not new crypto primitives!) is the key abstraction for scalable and attack-resilient blockchain state commitment.

Problem

• blockchain state commitment
• Merkle Patricia Trie
• tree height
• Nurgle attacks
• authenticated data structure

Innovation

• height-optimized
• authenticated data structure
• hierarchical proofs
• adaptive span
• Nurgle attack resilience