sha256.js

/**
 * @module sha256
 * Spec: https://nvlpubs.nist.gov/nistpubs/FIPS/NIST.FIPS.180-4.pdf
 * Resources:
 * - https://web.archive.org/web/20150315061807/http://csrc.nist.gov/groups/STM/cavp/documents/shs/sha256-384-512.pdf
 */

import * as binary from '../binary.js'
import * as math from '../math.js'

/**
 * @param {Uint8Array} data
 */
export const hash = data => {
  // Init working variables.
  /**
   * See 4.2.2: Constant for sha256 & sha224
   * These words represent the first thirty-two bits of the fractional parts of
   * the cube roots of the first sixty-four prime numbers. In hex, these constant words are (from left to
   * right)
   */
  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
  ])
  /**
   * See 5.3.3. Initial hash value.
   *
   * These words were obtained by taking the first thirty-two bits of the fractional parts of the
   * square roots of the first eight prime numbers.
   *
   * @todo shouldn't be a global variable
   */
  const H = new Uint32Array([
    0x6a09e667, 0xbb67ae85, 0x3c6ef372, 0xa54ff53a, 0x510e527f, 0x9b05688c, 0x1f83d9ab, 0x5be0cd19
  ])
  // "Message schedule" - a working variable
  const W = new Uint32Array(64)
  const M = new Uint32Array(16) // 512 bit - current "view" of the data
  let i = 0
  let isPaddedWith1 = false
  for (; i + 56 <= data.length;) {
    // write data in big endianess
    let j = 0
    for (; j < M.length && i + 3 < data.length; j++) {
      M[j] = data[i++] << 24 | data[i++] << 16 | data[i++] << 8 | data[i++]
    }
    if (i % 64 !== 0) { // there is still room to write partial content and the ending bit.
      M.fill(0, j)
      isPaddedWith1 = true
      while (i < data.length) {
        M[j] |= data[i] << ((3 - (i % 4)) * 8)
        i++
      }
      M[j] |= binary.BIT8 << ((3 - (i % 4)) * 8)
    }
    updateHash(H, W, K, M)
  }
  // write rest of the data, including the padding (using msb endiannes)
  let j = 0
  M.fill(0)
  for (; i < data.length; j++) {
    for (let ci = 3; ci >= 0 && i < data.length; ci--) {
      M[j] |= data[i++] << (ci * 8)
    }
  }
  // Write padding of the message. See 5.1.2.
  if (!isPaddedWith1) {
    M[j - (i % 4 === 0 ? 0 : 1)] |= binary.BIT8 << ((3 - (i % 4)) * 8)
  }
  // write length of message (size in bits) as 64 bit uint
  // @todo test that this works correctly
  M[14] = math.round(data.byteLength / binary.BIT29)
  M[15] = data.byteLength * 8
  updateHash(H, W, K, M)
  // correct H endianness and return a Uint8Array view
  const dv = new DataView(H.buffer)
  for (let i = 0; i < H.length; i++) {
    dv.setUint32(i * 4, H[i], false)
  }
  // logState(H)
  return new Uint8Array(H.buffer)
}

/**
 * @param {Uint32Array} H - @todo since this is manipulated, it should be lower case
 * @param {Uint32Array} W
 * @param {Uint32Array} K
 * @param {Uint32Array} M
 */
const updateHash = (H, W, K, M) => {
  // Step 1. Prepare message schedule
  for (let t = 0; t < 16; t++) {
    // @todo omit M, write to W directly in above function
    W[t] = M[t]
  }
  for (let t = 16; t < 64; t++) {
    W[t] = sigma1to256(W[t - 2]) + W[t - 7] + sigma0to256(W[t - 15]) + W[t - 16]
  }
  // Step 2
  let a = H[0]
  let b = H[1]
  let c = H[2]
  let d = H[3]
  let e = H[4]
  let f = H[5]
  let g = H[6]
  let h = H[7]
  // Step 3
  for (let t = 0; t < 64; t++) {
    const T1 = (h + sum1to256(e) + ch(e, f, g) + K[t] + W[t]) >>> 0
    const T2 = (sum0to256(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] += a
  H[1] += b
  H[2] += c
  H[3] += d
  H[4] += e
  H[5] += f
  H[6] += g
  H[7] += h
}

/**
 * @param {number} x
 * @param {number} y
 * @param {number} z
 */
const ch = (x, y, z) => (x & y) ^ (~x & z)

/**
 * @param {number} x
 * @param {number} y
 * @param {number} z
 */
const maj = (x, y, z) => (x & y) ^ (x & z) ^ (y & z)

/**
 * @param {number} w - a 32bit uint
 * @param {number} shift
 */
const rotr = (w, shift) => (w >>> shift) | (w << (32 - shift))

/**
 * Helper for SHA-224 & SHA-256. See 4.1.2.
 * @param {number} x
 */
const sum0to256 = x => rotr(x, 2) ^ rotr(x, 13) ^ rotr(x, 22)

/**
 * Helper for SHA-224 & SHA-256. See 4.1.2.
 * @param {number} x
 */
const sum1to256 = x => rotr(x, 6) ^ rotr(x, 11) ^ rotr(x, 25)

/**
 * Helper for SHA-224 & SHA-256. See 4.1.2.
 * @param {number} x
 */
const sigma0to256 = x => rotr(x, 7) ^ rotr(x, 18) ^ x >>> 3

/**
 * Helper for SHA-224 & SHA-256. See 4.1.2.
 * @param {number} x
 */
const sigma1to256 = x => rotr(x, 17) ^ rotr(x, 19) ^ x >>> 10