native/src/lib/sha256.ts

// Minimal SHA-256 implementation. Used to verify APK update downloads against
// the checksum published in the GitHub release body — the JS runtime has no
// built-in `crypto.subtle.digest` and we don't currently depend on
// `expo-crypto`. Public-domain algorithm (FIPS 180-4); typical sub-second per
// MB on a modern phone, which is fine for the rare update flow.

const K = new Uint32Array([
  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,
]);

function rotr(x: number, n: number): number {
  return (x >>> n) | (x << (32 - n));
}

export class Sha256 {
  private h = new Uint32Array([
    0x6a09e667, 0xbb67ae85, 0x3c6ef372, 0xa54ff53a,
    0x510e527f, 0x9b05688c, 0x1f83d9ab, 0x5be0cd19,
  ]);
  private buffer = new Uint8Array(64);
  private bufferLen = 0;
  private byteCount = 0;

  update(bytes: Uint8Array): void {
    let i = 0;
    this.byteCount += bytes.length;
    while (i < bytes.length) {
      const room = 64 - this.bufferLen;
      const chunk = Math.min(room, bytes.length - i);
      this.buffer.set(bytes.subarray(i, i + chunk), this.bufferLen);
      this.bufferLen += chunk;
      i += chunk;
      if (this.bufferLen === 64) {
        this.process(this.buffer);
        this.bufferLen = 0;
      }
    }
  }

  digestHex(): string {
    // Final block: append 0x80, pad with zeros, then 8-byte big-endian length.
    const totalBits = this.byteCount * 8;
    this.buffer[this.bufferLen++] = 0x80;
    if (this.bufferLen > 56) {
      while (this.bufferLen < 64) this.buffer[this.bufferLen++] = 0;
      this.process(this.buffer);
      this.bufferLen = 0;
    }
    while (this.bufferLen < 56) this.buffer[this.bufferLen++] = 0;
    // 64-bit length, big-endian. We can't represent >2^53 - JS bitops are
    // 32-bit, so split into hi/lo words.
    const hi = Math.floor(totalBits / 0x100000000);
    const lo = totalBits >>> 0;
    this.buffer[56] = (hi >>> 24) & 0xff;
    this.buffer[57] = (hi >>> 16) & 0xff;
    this.buffer[58] = (hi >>> 8) & 0xff;
    this.buffer[59] = hi & 0xff;
    this.buffer[60] = (lo >>> 24) & 0xff;
    this.buffer[61] = (lo >>> 16) & 0xff;
    this.buffer[62] = (lo >>> 8) & 0xff;
    this.buffer[63] = lo & 0xff;
    this.process(this.buffer);

    let out = '';
    for (let i = 0; i < 8; i++) {
      out += this.h[i].toString(16).padStart(8, '0');
    }
    return out;
  }

  private process(block: Uint8Array): void {
    const w = new Uint32Array(64);
    for (let i = 0; i < 16; i++) {
      w[i] =
        (block[i * 4] << 24) |
        (block[i * 4 + 1] << 16) |
        (block[i * 4 + 2] << 8) |
        block[i * 4 + 3];
    }
    for (let i = 16; i < 64; i++) {
      const s0 = rotr(w[i - 15], 7) ^ rotr(w[i - 15], 18) ^ (w[i - 15] >>> 3);
      const s1 = rotr(w[i - 2], 17) ^ rotr(w[i - 2], 19) ^ (w[i - 2] >>> 10);
      w[i] = (w[i - 16] + s0 + w[i - 7] + s1) | 0;
    }

    let a = this.h[0], b = this.h[1], c = this.h[2], d = this.h[3];
    let e = this.h[4], f = this.h[5], g = this.h[6], hh = this.h[7];

    for (let i = 0; i < 64; i++) {
      const S1 = rotr(e, 6) ^ rotr(e, 11) ^ rotr(e, 25);
      const ch = (e & f) ^ (~e & g);
      const temp1 = (hh + S1 + ch + K[i] + w[i]) | 0;
      const S0 = rotr(a, 2) ^ rotr(a, 13) ^ rotr(a, 22);
      const mj = (a & b) ^ (a & c) ^ (b & c);
      const temp2 = (S0 + mj) | 0;
      hh = g;
      g = f;
      f = e;
      e = (d + temp1) | 0;
      d = c;
      c = b;
      b = a;
      a = (temp1 + temp2) | 0;
    }

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

export function sha256Hex(bytes: Uint8Array): string {
  const h = new Sha256();
  h.update(bytes);
  return h.digestHex();
}