index.js

// barely-sha256.js

const K = [
  0x428a2f98, 0x71374491, 0xb5c0fbcf, 0xe9b5dba5, 0x3956c25b, 0x59f111f1, 0x923f82a4, 0xab1c5ed5,
  0xd807aa98, 0x12835b01, 0x243185be, 0x550c7dc3, 0x72be5d74, 0x80deb1fe, 0x9bdc06a7, 0xc19bf174,
  0xe49b69c1, 0xefbe4786, 0x0fc19dc6, 0x240ca1cc, 0x2de92c6f, 0x4a7484aa, 0x5cb0a9dc, 0x76f988da,
  0x983e5152, 0xa831c66d, 0xb00327c8, 0xbf597fc7, 0xc6e00bf3, 0xd5a79147, 0x06ca6351, 0x14292967,
  0x27b70a85, 0x2e1b2138, 0x4d2c6dfc, 0x53380d13, 0x650a7354, 0x766a0abb, 0x81c2c92e, 0x92722c85,
  0xa2bfe8a1, 0xa81a664b, 0xc24b8b70, 0xc76c51a3, 0xd192e819, 0xd6990624, 0xf40e3585, 0x106aa070,
  0x19a4c116, 0x1e376c08, 0x2748774c, 0x34b0bcb5, 0x391c0cb3, 0x4ed8aa4a, 0x5b9cca4f, 0x682e6ff3,
  0x748f82ee, 0x78a5636f, 0x84c87814, 0x8cc70208, 0x90befffa, 0xa4506ceb, 0xbef9a3f7, 0xc67178f2
];

const ROTR = (n, x) => (x >>> n) | (x << (32 - n));
const Σ0 = x => ROTR(2, x) ^ ROTR(13, x) ^ ROTR(22, x);
const Σ1 = x => ROTR(6, x) ^ ROTR(11, x) ^ ROTR(25, x);
const σ0 = x => ROTR(7, x) ^ ROTR(18, x) ^ (x >>> 3);
const σ1 = x => ROTR(17, x) ^ ROTR(19, x) ^ (x >>> 10);

const Ch = (x, y, z) => (x & y) ^ (~x & z);
const Maj = (x, y, z) => (x & y) ^ (x & z) ^ (y & z);

const toHexString = (byteArray) => Array.from(byteArray, byte => byte.toString(16).padStart(2, '0')).join('');

const preprocess = (message) => {
  const messageBits = [];
  for (let i = 0; i < message.length; i++) {
    messageBits.push(message.charCodeAt(i));
  }
  messageBits.push(0x80);
  while (messageBits.length % 64 !== 56) {
    messageBits.push(0x00);
  }
  let messageBitLength = message.length * 8;
  const lengthArray = new Array(8).fill(0);
  for (let i = 0; i < 8; i++) {
    lengthArray[7 - i] = messageBitLength & 0xFF;
    messageBitLength >>>= 8;
  }
  return messageBits.concat(lengthArray);
};

const sha256 = (message) => {
  const messageBits = preprocess(message);
  const H = [
    0x6a09e667, 0xbb67ae85, 0x3c6ef372, 0xa54ff53a,
    0x510e527f, 0x9b05688c, 0x1f83d9ab, 0x5be0cd19
  ];

  for (let i = 0; i < messageBits.length; i += 64) {
    const chunk = messageBits.slice(i, i + 64);
    const W = new Array(64);
    for (let t = 0; t < 16; t++) {
      W[t] = chunk[t * 4] << 24 | chunk[t * 4 + 1] << 16 | chunk[t * 4 + 2] << 8 | chunk[t * 4 + 3];
    }
    for (let t = 16; t < 64; t++) {
      W[t] = (σ1(W[t - 2]) + W[t - 7] + σ0(W[t - 15]) + W[t - 16]) >>> 0;
    }

    let [a, b, c, d, e, f, g, h] = H;

    for (let t = 0; t < 64; t++) {
      const T1 = (h + Σ1(e) + Ch(e, f, g) + K[t] + W[t]) >>> 0;
      const T2 = (Σ0(a) + Maj(a, b, c)) >>> 0;
      h = g;
      g = f;
      f = e;
      e = (d + T1) >>> 0;
      d = c;
      c = b;
      b = a;
      a = (T1 + T2) >>> 0;
    }

    H[0] = (H[0] + a) >>> 0;
    H[1] = (H[1] + b) >>> 0;
    H[2] = (H[2] + c) >>> 0;
    H[3] = (H[3] + d) >>> 0;
    H[4] = (H[4] + e) >>> 0;
    H[5] = (H[5] + f) >>> 0;
    H[6] = (H[6] + g) >>> 0;
    H[7] = (H[7] + h) >>> 0;
  }

  const hash = new Uint8Array(32);
  for (let i = 0; i < 8; i++) {
    hash[i * 4] = (H[i] >>> 24) & 0xFF;
    hash[i * 4 + 1] = (H[i] >>> 16) & 0xFF;
    hash[i * 4 + 2] = (H[i] >>> 8) & 0xFF;
    hash[i * 4 + 3] = H[i] & 0xFF;
  }

  return toHexString(hash);
};

module.exports = { sha256 };