Secure Hash Algorithm 256-bit (SHA-256)

SHA-256 (Secure Hash Algorithm 256-bit) is a cryptographic hash function belonging to the SHA-2 family, designed by the NSA (National Security Agency) and published in 2001.

A hash function is a mathematical algorithm that maps data of arbitrary size to a bit array of a fixed size. In the case of SHA-256, the output is always 256 bits (32 bytes) long, typically represented as a 64-character hexadecimal string.

Key Properties

Like all good cryptographic hash functions, SHA-256 possesses several critical properties:

1. Deterministic: The same input will always produce the exact same output hash.
2. Fast Computation: It is relatively quick to compute the hash for any given message.
3. Pre-image Resistance (One-way): It is computationally infeasible to reverse the process — you cannot generate the original message from its hash value.
4. Avalanche Effect: A tiny change in the input (even a single bit) produces an entirely different and uncorrelated output hash.
5. Collision Resistance: It is computationally infeasible to find two different inputs that produce the exact same hash output.

Common Use Cases

• Password Hashing: Storing passwords securely in databases (though algorithms like bcrypt or Argon2 are preferred as they include key stretching to slow down brute-force attacks).
• File Integrity: Verifying that a downloaded file hasn't been corrupted or tampered with by comparing its hash against a known good hash provided by the author.
• Blockchain and Cryptocurrencies: SHA-256 is the core proof-of-work algorithm used in Bitcoin mining and block creation.
• Digital Signatures: Ensuring the authenticity of digital documents or software updates.