What is Hash (Cryptographic Hash)

A cryptographic hash is a mathematical function that takes any input data a word, a document, an entire blockchain block and produces a fixed-length output called a hash digest or simply a hash. Hash functions are the fundamental cryptographic building block securing every blockchain in existence.

THE PROPERTIES OF CRYPTOGRAPHIC HASH FUNCTIONS

Deterministic: The same input always produces the exact same output hash. Verify any data by re-hashing and comparing.
Fixed Output Length: Regardless of input size whether one byte or one terabyte the output is always the same length. SHA-256 always outputs exactly 256 bits (64 hexadecimal characters).
Avalanche Effect: A single character change in the input completely and unpredictably changes the entire output hash. There is no similarity between the hash of "Hello" and "hello" they look completely unrelated.
One-Way (Pre-image Resistance): It is computationally infeasible to reverse a hash back to its original input. Given a hash output, you cannot reconstruct the input without brute-force guessing every possibility.
Collision Resistance: It is computationally infeasible to find two different inputs that produce the same hash output.

HASH FUNCTIONS USED IN BLOCKCHAIN

SHA-256 (Secure Hash Algorithm 256): Used by Bitcoin for block hashing and proof-of-work mining. SHA-256 produces a 256-bit (32-byte) hash. Mining Bitcoin requires finding an input that produces a SHA-256 hash below a target value requiring trillions of attempts.
Keccak-256: Used by Ethereum. Similar security properties to SHA-256 but with different internal construction. All Ethereum addresses are derived from Keccak-256 hashes of public keys.

HOW HASHES CHAIN BLOCKS

Each block contains the hash of the previous block in its header. This creates the "chain" in blockchain: changing any transaction in any historical block would change that block's hash, which would invalidate the next block's reference to it, cascading invalidation forward through every subsequent block. The chain provides immutability through this hash linkage.

Terms in addition to the Hash (Cryptographic Hash)

Blockchain

A blockchain is a subset of a distributed database. The Bitcoin inventors originally prototyped the system in 2008. This modern database is made up of separate blocks that are connected together in a chronological chain. Blockchains may be used to store a wide range of data types. It has mostly been utilized as a public ledger for bitcoin transactions to date. A peer-to-peer network comprised of independent nodes uses a consensus process to ensure the blockchain's security and legitimacy. Each node in the network keeps a public and immutable copy of the data.

2 Factor Authentication (2FA)

2 Factor Authentication is a security measure with two layers. It is used by the majority of cryptocurrency exchanges. To log in, you must provide not only a password, but also a code obtained, for example, from the Google authenticator.

Airdrop

An airdrop is a method of distributing coins. End users can typically obtain coins for free or in exchange for doing a small task, such as subscribing to a newsletter, sending a tweet, or inviting others via a personal affiliate link. Cryptocurrency airdrops — the act of depositing cryptocurrency into public crypto wallets — are utilized as a marketing, liquidity creation, and network bootstrapping technique for many different types of blockchain initiatives.

Altcoin

Altcoin - "alternative coin" - is any kind of digital currency other than Bitcoin. Since the launch of Bitcoin, the world's first digital currency, many altcoins (as well as supporting blockchains) have been created. Altcoin digital currencies share many similarities to Bitcoin, but consistently and have significant differences. There are about 20,000 altcoins, and this number is expected to grow significantly in the coming years. Altcoins often develop Bitcoin features. Ethereum, currently the most widely used blockchain, supports digital contracts and separate applications where Bitcoin does not. Altcoins are also often created to cater to the needs of different users. The Litecoin blockchain, for example, can process payments quarterly for the duration of Bitcoin.

Cold Storage

Cold storage is the way to store cryptocurrency offline. The word refers to the use of offline wallets that are not connected to the internet. Cold storage is the most secure way to keep cryptocurrencies since an offline currency becomes less likely to be hacked and stolen. Paper wallets, printed renditions of private keys, and offline hardware and software wallets are all examples of cold storage.