SHA256 Usage Patterns

Common use cases and implementation patterns for SHA-256

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SHA256 Usage Patterns

Common patterns and real-world examples for using SHA-256.

Bitcoin Address Derivation

Bitcoin P2PKH addresses use SHA-256 + RIPEMD-160:

import { SHA256 } from '@tevm/voltaire/SHA256';
import { Ripemd160 } from '@tevm/voltaire/Ripemd160';

function publicKeyToAddress(publicKey: Uint8Array): Uint8Array {
  // Step 1: SHA-256 hash of public key
  const sha256Hash = SHA256.hash(publicKey);

  // Step 2: RIPEMD-160 hash of SHA-256 hash
  const ripemd160Hash = Ripemd160.hash(sha256Hash);

  return ripemd160Hash; // 20-byte address payload
}

Double SHA-256 (Bitcoin)

Bitcoin uses double SHA-256 for blocks and transactions:

function doubleSha256(data: Uint8Array): Uint8Array {
  return SHA256.hash(SHA256.hash(data));
}

// Bitcoin block hash
const blockHeader = new Uint8Array(80);
const blockHash = doubleSha256(blockHeader);

Merkle Trees

Build authenticated data structures:

function merkleRoot(leaves: Uint8Array[]): Uint8Array {
  if (leaves.length === 0) throw new Error('No leaves');
  if (leaves.length === 1) return SHA256.hash(leaves[0]);

  let level = leaves.map(leaf => SHA256.hash(leaf));

  while (level.length > 1) {
    const next: Uint8Array[] = [];
    for (let i = 0; i < level.length; i += 2) {
      const left = level[i];
      const right = level[i + 1] || left;
      const combined = Bytes64();
      combined.set(left, 0);
      combined.set(right, 32);
      next.push(SHA256.hash(combined));
    }
    level = next;
  }

  return level[0];
}

HMAC-SHA256

Message authentication:

function hmacSha256(key: Uint8Array, message: Uint8Array): Uint8Array {
  const blockSize = 64;

  let derivedKey = key.length > blockSize
    ? SHA256.hash(key)
    : key;

  const paddedKey = new Uint8Array(blockSize);
  paddedKey.set(derivedKey);

  const opad = new Uint8Array(blockSize).fill(0x5c);
  const ipad = new Uint8Array(blockSize).fill(0x36);

  for (let i = 0; i < blockSize; i++) {
    opad[i] ^= paddedKey[i];
    ipad[i] ^= paddedKey[i];
  }

  const innerHash = SHA256.hash(new Uint8Array([...ipad, ...message]));
  return SHA256.hash(new Uint8Array([...opad, ...innerHash]));
}

File Integrity Checking

async function hashFile(file: File): Promise<string> {
  const hasher = SHA256.create();
  const chunkSize = 1024 * 1024;

  for (let offset = 0; offset < file.size; offset += chunkSize) {
    const chunk = await file.slice(offset, offset + chunkSize).arrayBuffer();
    hasher.update(new Uint8Array(chunk));
  }

  const hash = hasher.digest();
  return SHA256.toHex(hash);
}

Content Addressing

function contentId(data: Uint8Array): string {
  const hash = SHA256.hash(data);
  return SHA256.toHex(hash);
}

// Usage in cache
const cache = new Map<string, Uint8Array>();
const id = contentId(data);
cache.set(id, data);

Certificate Fingerprints

function certificateFingerprint(derCert: Uint8Array): string {
  const hash = SHA256.hash(derCert);
  // Format as colon-separated hex
  return Array(hash)
    .map(b => b.toString(16).padStart(2, '0'))
    .join(':')
    .toUpperCase();
}

See Also

• API Reference
• Security
• Performance