What is a Merkle Tree?
A Merkle Tree is a data structure commonly used in blockchain and cryptography. Introduced by computer scientist Ralph Merkle in 1987, the Merkle Tree can effectively verify the integrity of large amounts of data and is widely used in blockchains to ensure the security and consistency of transaction data.
The hash function is the core of the Merkle tree structure. The basic idea of a Merkel tree is to split a large amount of data into small chunks and then perform hash calculations layer by layer until a root hash value is generated. This root hash value can be used to verify the integrity of the entire data set. If any of the data chunks changes, then its hash value will change, which affects the upper hash value and ultimately leads to a change in the root hash value. Therefore, by comparing the root hash, it is possible to quickly verify that the data is complete and untampered with.
The working principle of Merkle tree:
1. Slicing the data: first, the data to be verified is split into a number of fixed-size data blocks. If the number of data blocks is not even, the last data block can be copied until the number of data blocks is even. (For example, suppose that a data file is divided into eight parts below, and each segment is named A through H respectively. Subsequently, each segment is substituted into a hash function, resulting in eight different hash values.)
(With the hash function, the hash values of the eight segments are calculated.)
2. hash calculation: hash calculation is performed for each data block to get the hash value. In other words, we perform hash operations with hA + hB, hC + hD, hE + hF, and hG + hH. The result will yield four hash values.
3. Constructing a binary tree: We repeat the above hash computation process and perform the next round of merge hash operation until we get two hash values. These two hashes are then merged until eventually there is only one root hash, the Merkel root (also known as the root hash). In this way a binary tree structure is constructed, where the leaf nodes of the tree are the hashes of the data block, and the non-leaf nodes are the result of the splicing of the hashes of their children.
4. Root Hash: The final root hash is the value of the root node of the Merkel tree, which can be used to verify the integrity of the entire data set.
(The structure looks like an inverted tree. A row of leaves at the bottom, combining with each other to produce nodes, and finally the root.)
Overall, Merkel trees work by providing an efficient way to verify the integrity of large amounts of data through hash calculations and binary tree structures.
To summarize, the function of a Merkel tree is to verify the integrity of a large amount of data by dividing the data into multiple copies and then repeatedly hashing the data to eventually form the Merkel root.
Why is the Merkel Root used in Bitcoin?
In blockchain, Merkel trees are widely used to verify the integrity of transaction data. The transaction data in each block is organized into the structure of a Merkel tree, and the block header contains the root hash of this Merkel tree. With the transaction hash value (TXID) of each transaction in the block, we get the leaves of the tree. When a node receives a new block, it can verify that the transaction data in the block is complete and untampered by comparing the root hash in the block header with the recalculated root hash. In this case, the Merkle root has multiple uses. Let's take a look at the applications of Merkle root in cryptocurrency mining and transaction verification.
1. Mining - Transaction Data Integrity Verification: Bitcoin blocks contain a large amount of transaction data. The first part is the block header, which is fixed in size and contains the block metadata. The second part is the block body, which is variable in size but usually much larger than the block header, and contains a list of transactions. Miners need to repeatedly hash the data until they produce a result that meets specific conditions to mine a valid block. To get the right result, they need to make trillions of attempts. On each attempt, the miner changes the random number in the block header, known as the Nonce value, to generate a different result. However, the rest of the block stays the same, with thousands of transactions in it, which still need to be hashed each time.
Merkel Root, on the other hand, greatly simplifies this process. When mining begins, all the transaction queues are packed and constructed into a Merkle tree, and the resulting 32-bit root hash is placed into the block header. Subsequently, there is no need to hash the entire block, and by comparing the Merkel root in the block header to the recalculated Merkel root, it is possible to quickly verify that the transaction data in the block is complete and untampered with. The list of transactions in the valid block header cannot be modified, otherwise the Merkel root will be changed. After the block is sent to other nodes, the root hash will be calculated from the transaction list. If it does not match with the value in the block header, the block can be rejected.
2. Lightweight Node Verification: Lightweight nodes in the Bitcoin network (e.g., wallet clients) typically do not download all the transaction data stored for the entire blockchain and hash it. Instead, they can confirm the validity of a transaction by verifying the Merkle root in the block header. This approach can greatly reduce network bandwidth and storage space requirements, allowing lightweight nodes to more quickly validate transactions and participate in the Bitcoin network.
3. Simplified SPV Proof: SPV (Simple Payment Verification) is a simplified method for verifying Bitcoin transactions that confirms the existence of a particular transaction by verifying the Merkel root in the block header. This method makes it possible to validate transactions and make payments in resource-constrained environments such as mobile devices.
Overall, the use of the Merkel root in Bitcoin is primarily intended to provide an efficient method of verifying the integrity of transaction data, while also facilitating lightweight nodes and SPV proofs. With Merkle Root, the Bitcoin network can ensure the security and consistency of transaction data while improving the efficiency and scalability of the entire network.
Summarizing
The Merkel tree has proven itself to be important in computer science applications, and as we have seen, it is also quite valuable in blockchain. Merkel trees make it easier to verify information in distributed systems and avoid congestion of redundant data in the network.
Without Merkel trees and Merkel roots, Bitcoin and other cryptocurrency blocks would not be as compact as they are today. While lightweight clients lack advantages in terms of privacy and security, with Merkel Proof, users are able to verify that transactions are counted in the block with minimal fees.
Overall, Merkel Tree Proof provides an efficient way to verify the integrity of large amounts of data by means of hash calculations, without the need to compare the entire data set one by one. This makes the Merkle tree one of the important data structures in blockchain for ensuring the security and consistency of transaction data.
