What is a Block Header?<\/strong><\/h4>\nThe block header is made up of metadata (data about data). It helps to verify the validity of a block.
\nAs you can see in the architecture diagram, the block header of a block consists of:
\n\u2022 Version
\n\u2022 Timestamp
\n\u2022 Hash
\n\u2022 Difficulty-Level
\n\u2022 Nonce
\n\u2022 Merkle Root<\/p>\n
What is a Hash? Why it is called as \u201cthe backbone\u201d of a blockchain network?<\/strong>
\nA hash is a cryptographic algorithm or function that converts an input string (numbers, alphabets, media files etc.) of any length into an encrypted output or \u201cchecksum\u201d of a fixed length. The process of applying a hash algorithm to any data is called hashing.<\/p>\nThe checksum points at the exact data input\u200a\u2014\u200aif just a single byte differs between two files, the outputs after hashing will be two completely strings. This means that a small change in your input can drastically change your output.<\/p>\n
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Different blockchains use different hashing algorithms. For example, if we talk about Bitcoin, it uses the Secure Hashing Algorithm 256 (aka SHA256), which produces a 32-byte hash.<\/p>\n
The usefulness of the hashing process is that you can\u2019t reverse-engineer a hash, i.e. you won\u2019t be able to work backward from an output string to determine the input data.<\/p>\n
Hashing is indeed an integral part of the blockchain. It is essentially a feature that gives security capabilities to the processed transactions, making them immutable. That is why it is called as the backbone of a blockchain network.<\/p>\n
Previous Hash<\/strong>
\nHashing of a particular block involves using the meta-data of the previous block while producing a new hash for it. This creates a link between the block and the chain and thus it becomes technically \u201cunbreakable.” Hereafter, no one can delete or modify the data of the block stored in the blockchain; if someone attempts this, the successive block rejects the modification (as the hash of block won’t be valid any longer) \u2013 thus, if data is tampered with, the blockchain will break; this characteristic is not found in traditional databases, where information can be modified or deleted with ease.<\/p>\nWhat is a Nonce?<\/strong>
\nAs discussed above, nonce is an abbreviation for “number only used once.” Technically, it is a pseudo-random number that is utilized as a counter during the process of mining.<\/p>\nAs the hash value is the same no matter how many times it is calculated, the nonce is utilized to change the value and search for a number which is lower than the difficulty.<\/p>\n
Too much technical? Well, here\u2019s a simplified explanation:<\/p>\n
In proof-of-work systems like blockchain, a nonce is used to make the task of generating a valid hash more difficult. This means that blockchain miners need to find a nonce value that, when merged with the hashing algorithm, generates an output that meets certain requirements.<\/p>\n
What is a Merkle Root?<\/strong>
\nIn order to understand what a Merkle Root is, you need to first understand the concept of Merkle Tree.<\/p>\nMerkle Tree<\/strong>
\nA Merkle Tree, or binary hash tree, is used to encrypt the blockchain data in a secure and efficient way. It facilitates quick verification and fast movement of large sets of blockchain data (from one node to the other on the blockchain network).<\/p>\nA Merkle Tree is constructed through bottom-up approach by repeatedly calculating hashing pairs of nodes until there is only one hash left.<\/p>\n
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In the above tree diagram, we can observe that input of data is broken up into blocks labelled B1 though B4. The first step is to hash each data block using a particular hashing algorithm (e.g. MD5, SHA256, SHA1, and SHA512). With this, the blocks Hash 0-0, Hash 0-1, Hash 1-0, and Hash 1-1 are created. This is the primary step for developing a Merkle Tree. These blocks can be referred as leaves of the Merkle Tree. There must be at least two leaves (there isn\u2019t any upper limit).<\/p>\n
Next, two adjacent hashes are merged into a single hash. So, Hash 0-0 is chained with Hash 0-1 and is hashed again by means of a hashing algorithm. The result is Hash 0. Similarly, Hash 1-0 and Hash 1-1 blocks yield Hash 1. The process continues until a single hash is generated. The final hash what you get is referred to as Merkle Root.<\/p>\n
Hence, we can say that a Merkle Tree formation is the process of making a single hash from a group of hashes.<\/p>\n
Merkle Root<\/strong>
\nThe single hash that is produced by the Merkle Tree is called the Merkle Root. Each block in a blockchain has exactly one of it \u2013 it is like a fingerprint for all the transactions in a block.<\/p>\nA Merkle Root is used as one of the fields in a block header in order to have a short representation of every transaction inside the block.<\/p>\n
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