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Ethereum: Adding Merkle tree hashes instead of chaining

Published by Terlumun Aondover on February 5th, 2025.

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Adding, rather than combining, hashes in Merkle Trees: A Security Perspective

As the Ethereum blockchain grows in popularity, the underlying technology remains a subject of interest for developers, researchers, and security experts. In this article, we will delve into the current practice of generating Merkle trees on Ethereum, focusing on why adding hashes is often preferred over combining them. We will also discuss potential security holes and vulnerabilities that could result from this approach.

Merkle Trees: A Brief Overview

A Merkle tree is a data structure used to efficiently store and retrieve large amounts of data. It is particularly useful for storing cryptographic hash values, such as those generated by Ethereum digital signatures. The tree consists of a root node that contains the hashes of its child nodes. Each leaf node contains a single value.

Concatenation vs. Concatenation. addition: Commutative operation

When concatenating (or combining) two strings using the + operator, the order in which they are concatenated does not matter. In other words, "hello" + "world" produces the same result as "world" + "hello". This commutative property makes concatenation a convenient operation for manipulating strings.

By contrast, adding two numbers (e.g. 5 + 3) is not commutative; the order of the operands does matter. For example, 5 + 3 equals 8, but 3 + 5 equals 8. This property makes addition more suitable for numerical computations.

Why concatenation is preferred over Merkle trees

In the context of the Ethereum blockchain, combining hashes to form a Merkle tree allows for efficient data storage and retrieval. Here are some reasons why adding hashes is often preferred over combining them:

Data integrity: By storing multiple hashes together, we can ensure that the data remains consistent across nodes in the tree. This is especially important for large data sets or sensitive information.

Efficient storage
: Combining hashes reduces the number of storage requirements since each node contains only a single hash value.

Scalability: Merkle trees are designed to handle large amounts of data without significantly degrading performance.

Potential vulnerabilities and security flaws

While combining is generally a secure operation, there are some potential vulnerabilities to be aware of:

Reversibility: If an attacker gains control of the Ethereum blockchain, they can attempt to reverse the Merkle tree by manipulating individual hash values. This can lead to data breaches and even theft of confidential information.

Key exchange vulnerabilities: In a situation where multiple parties need to exchange cryptographic keys using Merkle trees, an attacker can exploit vulnerabilities in the encryption algorithms used for key exchange (e.g. Diffie-Hellman key exchange).

Conclusion

In summary, adding hashes instead of combining them is often preferred when generating Merkle trees on Ethereum due to its inherent security properties. While there are potential loopholes and vulnerabilities associated with this approach, they can be mitigated through careful implementation and appropriate security measures.

As the Ethereum ecosystem grows, it is important for developers and researchers to stay up-to-date with the latest developments in blockchain security. By understanding the trade-offs between different data storage mechanisms, we can create more secure and scalable solutions for building robust blockchain applications.

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