SHA-256

2 min read

Pronunciation

[es-eych-ey too fif-tee siks]

Analogy

SHA-256 works like a document shredder with very specific properties—it takes documents of any size and turns them into precisely 32-byte confetti piles. No matter how big or small the original document, the confetti pile is always exactly the same size. The slightest change to the original document (even a single comma) creates an entirely different confetti pattern, and it's practically impossible to reconstruct the original document from the confetti.

Definition

A cryptographic that produces a 256-bit (32-byte) value, widely used in systems particularly . SHA-256 (Secure Algorithm 256-bit) is part of the SHA-2 family developed by the NSA and published by NIST.

Key Points Intro

SHA-256 provides the cryptographic backbone for and many other systems.

Key Points

Transforms data of any length into a fixed 256-bit (32-byte) output.

Forms the core of Bitcoin's proof-of-work mining algorithm and transaction verification.

Produces drastically different outputs even when inputs differ by a single bit.

Considered cryptographically secure against current computing capabilities.

Example

In , repeatedly modify a header and calculate its SHA-256 (actually applying the function twice in sequence) until they find a value with a specific number of leading zeros, proving they've performed the computational work required to validate a .

Technical Deep Dive

SHA-256 processes messages in 512-bit blocks after the input to appropriate length and appending the original message length. The algorithm initializes with eight 32-bit words derived from the square roots of the first eight prime numbers, creating a seemingly random but verifiable starting . Each message undergoes 64 rounds of processing using the compression function, which applies a mixture of bitwise operations (AND, OR, XOR, rotations) and modular addition. These operations thoroughly mix the message into the intermediate , creating the strong effect where a single bit change propagates unpredictably through the entire . applies SHA-256 twice (SHA-256d) for additional security, while many derived cryptocurrencies use alternative algorithms (like or Equihash) specifically designed to resist ASIC optimization, though others like Cash and SV maintain the original SHA-256 algorithm.

Security Warning

While SHA-256 remains secure against current attacks, implement it correctly. Common implementation mistakes include not handling data encoding properly, insufficient input validation, or improper processing of multiple data segments, which can lead to issues like length extension attacks in some applications.

Caveat

SHA-256, like all fixed-output functions, is theoretically vulnerable to collision attacks due to the pigeonhole principle, though finding actual collisions remains computationally infeasible. Additionally, quantum computing advances may eventually necessitate migration to quantum-resistant alternatives.

Related Terms

Hash Function

Cryptography

Blockchain & Cryptocurrency Glossary

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