What is a Merkle tree?

A section from the Encyclopedia of Database Systems states, “Merkle trees are data structures devised to authenticate, with a unique signature, a set of messages, by at the same time making an intended verifier able to verify authenticity of a single message without the disclosure of the other messages.”

It is designed to efficiently verify the consistency of data by organizing individual elements into a hierarchical structure. Its application is especially useful in blockchain technology, where large amounts of data have to be verified across decentralized networks.

How it works 

1. Merkle trees start with individual data blocks or transactions at the bottom, known as leaf nodes.
2. Each leaf node is assigned a unique hash value based on its data content.
3. These hashes are paired and combined to form branch nodes.
4. This process continues until only one node remains at the top, which represents the entire dataset through its hash value.
5. Any change in a data block will alter its hash and start a chain reaction up to the Merkle root, allowing for efficient detection of tampering or corruption.

The main components 

1. Leaf nodes: These are the bottom-most nodes, each representing an individual data block or transaction and containing its corresponding hash value.
2. Branch nodes: These nodes serve as intermediaries between leaf nodes and the root node.
3. Root node (Merkle root): This is the top-most node, encapsulating the entire dataset through its unique hash value derived from all lower-level hashes.
4. Hash functions: Cryptographic algorithms are used to generate unique digital fingerprints for each node's content, ensuring data integrity and authenticity throughout the tree structure.

The benefit to healthcare 

Merkle trees are part of blockchain technology. The common applications range from longitudinal healthcare records to interoperability support in population initiatives for large health systems, with Merkle trees acting as privacy support for systems. Blockchains rely on decentralization so that data remains unchanged once recorded. 

Merkle trees allow for the efficient verification that no unauthorized changes have occurred during transmission or storage. By using Merkle trees as part of a larger access control framework, organizations can implement fine-grained access controls over sensitive attributes.

Related: HIPAA Compliant Email: The Definitive Guide

FAQs

How does a Merkle tree help verify a specific transaction in a block without downloading the entire block?

By providing a "Merkle proof" or "Merkle path." This path includes the necessary intermediate hash values to recompute the Merkle root from the transaction's hash, allowing verification against the known root.

How do Merkle trees contribute to Simplified Payment Verification (SPV) clients in blockchain?

SPV clients only download block headers, which include the Merkle root. They can then request Merkle proofs for specific transactions to verify their inclusion in a block without needing the full block data.