What Is SHA-256?
SHA-256 is a hashing algorithm. SHA stands for Secure Hashing Algorithm, and the number “256” represents the algorithm’s output in bits; SHA-256 outputs a 256-bit hash.
The algorithm is part of the SHA-2 family of hashing algorithms (incl., SHA-224, SHA-384, and SHA-512) developed by the U.S. National Security Agency (NSA).
Hashing algorithms are most commonly used for cryptographic purposes. They’re used to secure connections over the Internet, facilitate end-to-end encryption, mine new blocks on a blockchain, and more.
SHA-256 is by far the most commonly used and well-known SHA-2 algorithm. It is also used in the world’s first cryptocurrency, Bitcoin.
How Does SHA-256 Work?
Note: Explaining how SHA-256 works in detail goes far beyond the scope of this text. There is a lot of complex maths and computer science involved. Explore this thorough technical explanation of SHA-256.
Now let’s understand how the SHA-256 algorithm works in principle:
Simply said, what SHA-256 and all hashing algorithms do is take a piece of textual information of any content and length and convert it into a fixed-length text called a hash.
Hashing works so that even if a single character in the input text changes, the hash will be completely different.
The SHA-256 compression function operates on a 512-bit message block and a 256-bit intermediate hash value. It is essentially a 256-bit block cipher algorithm which encrypts the intermediate hash value using the message block as key [sic].
EIPS (n.d.)
This is incredibly useful in cryptography, where you often want to ensure data integrity without revealing the data itself.
For example, a website that requires a login doesn’t need to store your password, it only needs to know its hash value. Once you enter the password, it will be processed with an SHA-256 or similar algorithm to verify it’s the same without you ever having to disclose it.
Finally, SHA-256 is an irreversible hashing function, meaning that it is near-impossible to derive its input from its output (i.e., the hash).
SHA-256 in Cryptocurrency
The SHA-256 hashing algorithm plays an important role in crypto and blockchain. Miners run this function continuously while mining Bitcoin and other proof-of-work (PoW) (i.e., mining-based) blockchains in search of a matching hash value.
The security of the blockchain comes from the chaining of hash values representing blocks. This makes undoing previous blocks virtually impossible without a majority consensus (i.e., 51%).
SHA-256 is also used to create and verify digital signatures associated with transactions on the blockchain.
Evaluating the Security of SHA-256
SHA-256 is used worldwide for countless applications; however, technological advancements in computing have recently questioned its future security.
Increases in computing power and the advent of quantum computers are pushing future-minded developers toward new hashing solutions. SHA-3 is one such solution, developed as an advancement of SHA-256 that features performance improvements and better quantum resistance.
Conclusion
SHA-256 is still a robust, secure, and widely used hashing algorithm. It has stood the test of time and serves as the backbone of modern-day cryptography.
Ethereum.org. (n.d.). Descriptions of SHA-256, SHA-384, and SHA-512. EIPS.
https://eips.ethereum.org/assets/eip-2680/sha256-384-512.pdf
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