SHA-256 Hashing Explained

What is a Hash Function?

A hash function takes arbitrary input and produces a fixed-length output (digest). SHA-256 produces 256 bits (64 hex characters).

Key Properties

• One-way: Cannot reconstruct input from the hash
• Collision resistance: Extremely unlikely for two different inputs to produce the same hash
• Deterministic: Same input always produces the same hash

Use Cases

• Password storage: Store hash (+ salt), never plaintext
• File integrity: Verify downloaded files haven't been tampered with
• Digital signatures: Generate message digest for signing
• Cache keys: Unique content identifiers

Web Crypto API Implementation

async function sha256(text) {
  const encoder = new TextEncoder();
  const data = encoder.encode(text);
  const hashBuffer = await crypto.subtle.digest('SHA-256', data);
  const hashArray = Array.from(new Uint8Array(hashBuffer));
  return hashArray.map(b => b.toString(16).padStart(2, '0')).join('');
}

const hash = await sha256('Hello, World!');
// dffd6021bb2bd5b0af676290809ec3a53191dd81c7f70a4b28688a362182986d

Summary

SHA-256 can be computed entirely in-browser using the native Web Crypto API — no libraries required and no data leaves the device.