What is a Merkle Tree?

A Merkle tree, also known as a binary hash tree, is a data structure used in cryptography to validate the integrity of data within a large set of information. It is named after Ralph Merkle, who first described the concept in a 1987 paper.

In a Merkle tree, each leaf node contains a data block, while each non-leaf node contains a hash value. The hash value is calculated by applying a cryptographic hash function to the values of its child nodes. This creates a tree-like structure where each parent node is the hash of its children. The root node of the tree represents the hash value of the entire data set.

One of the main benefits of using a Merkle tree is that it allows for efficient data verification. If any part of the data changes, the corresponding hash value will change, and this change will propagate up the tree. By only storing the root hash, it is possible to verify the integrity of the entire data set without having to store the entire data set.

Merkle trees are commonly used in distributed systems, such as blockchains. In blockchain systems, the data blocks represent transactions, and the Merkle tree allows for the efficient verification of the validity of the transactions within a block.

In summary, a Merkle tree is a data structure that enables the efficient validation of data within a large set of information. It uses a tree-like structure to store hash values, and it is commonly used in distributed systems, such as blockchains, to verify the integrity of data.

Simplified Example

A Merkle tree can be compared to a baking contest. Imagine you are baking a cake with different layers, each layer representing a part of a large amount of data. Each layer has ingredients, and you mix them together to make the batter. You then put the batter in the oven to bake it into a cake layer.

Now imagine you are having a contest with your friends to see who made the best cake. You all bring your cakes, and the judges taste a small piece from each cake. They write down the ingredients of each cake, and they use this information to identify which cake is the best.

In a similar way, a Merkle tree is used to identify which data is the real and correct data, out of a large amount of data. Instead of writing down the ingredients, a special computer program mixes the data together to make a unique identifier, called a hash. The program puts the hashes in a tree-like structure, with each hash representing a part of the data. The root of the tree is the final hash that represents the entire data.

Just like the judges in the cake contest, someone can check the data by looking at the hashes in the Merkle tree. If any part of the data changes, the hashes will change, and this change will be noticeable all the way up to the root hash. This way, the person can make sure the data is correct and hasn't been changed by someone else.

Who Invented the Merkle Tree?

The term "Merkle tree" was coined after Ralph Merkle, who patented it in 1979. Although the concept has earlier roots, with similar ideas found in the works of Lamport in 1978 and Haber and Stornetta in 1991, Merkle is acknowledged for formalizing and christening it as the "Merkle tree." Beyond inventing the concept, Merkle played a crucial role in exploring its diverse applications, particularly in fields such as cryptography and distributed computing.

Examples

Bitcoin blockchain: The Bitcoin blockchain uses Merkle trees to efficiently verify the integrity of transactions within a block. The transactions are organized into leaf nodes in the tree, and the root node represents the hash of all the transactions in the block.

IPFS (InterPlanetary File System): IPFS is a decentralized file storage and distribution system that uses Merkle trees to verify the integrity of the data stored in the network. Each file is broken down into smaller blocks, and the blocks are organized into a Merkle tree to create a unique identifier for the file.

Ethereum blockchain: The Ethereum blockchain uses Merkle trees to efficiently verify the state of the system. The state is represented by a tree of account balances, and the Merkle tree allows for the efficient validation of these balances without having to store the entire state of the system.

Related Terms

• Cryptographic Hash Function: A mathematical algorithm that takes in data of arbitrary size and produces a fixed-size output, commonly referred to as a hash or a digest.

• Node: An essential component of blockchain technology.