diff --git a/array.js b/array.js
index 02b5389..30c6aff 100644
--- a/array.js
+++ b/array.js
@@ -164,3 +164,21 @@ export const uniqueBy = (arr, mapper) => {
   }
   return result
 }
+
+/**
+ * @template {ArrayLike<any>} ARR
+ * @template {function(ARR extends ArrayLike<infer T> ? T : never, number, ARR):any} MAPPER
+ * @param {ARR} arr
+ * @param {MAPPER} mapper
+ * @return {Array<MAPPER extends function(...any): infer M ? M : never>}
+ */
+export const map = (arr, mapper) => {
+  /**
+   * @type {Array<any>}
+   */
+  const res = Array(arr.length)
+  for (let i = 0; i < arr.length; i++) {
+    res[i] = mapper(/** @type {any} */ (arr[i]), i, /** @type {any} */ (arr))
+  }
+  return /** @type {any} */ (res)
+}
diff --git a/buffer.js b/buffer.js
index 3d50186..5d76ece 100644
--- a/buffer.js
+++ b/buffer.js
@@ -6,6 +6,8 @@
 
 import * as string from './string.js'
 import * as env from './environment.js'
+import * as array from './array.js'
+import * as math from './math.js'
 import * as encoding from './encoding.js'
 import * as decoding from './decoding.js'
 
@@ -81,6 +83,27 @@ export const toBase64 = env.isBrowser ? toBase64Browser : toBase64Node
 /* c8 ignore next */
 export const fromBase64 = env.isBrowser ? fromBase64Browser : fromBase64Node
 
+/**
+ * Base64 is always a more efficient choice. This exists for utility purposes only.
+ *
+ * @param {Uint8Array} buf
+ */
+export const toHexString = buf => array.map(buf, b => b.toString(16).padStart(2, '0')).join('')
+
+/**
+ * Note: This function expects that the hex doesn't start with 0x..
+ *
+ * @param {string} hex
+ */
+export const fromHexString = hex => {
+  const hlen = hex.length
+  const buf = new Uint8Array(math.ceil(hlen / 2))
+  for (let i = 0; i < hlen; i += 2) {
+    buf[buf.length - i / 2 - 1] = Number.parseInt(hex.slice(hlen - i - 2, hlen - i), 16)
+  }
+  return buf
+}
+
 /**
  * Copy the content of an Uint8Array view to a new ArrayBuffer.
  *
diff --git a/buffer.test.js b/buffer.test.js
index 8cbd5f5..e9458ec 100644
--- a/buffer.test.js
+++ b/buffer.test.js
@@ -7,7 +7,7 @@ import * as prng from './prng.js'
  */
 export const testRepeatBase64Encoding = tc => {
   const gen = tc.prng
-  const barr = prng.uint8Array(gen, 100000)
+  const barr = prng.uint8Array(gen, prng.uint32(gen, 0, 47))
   const copied = buffer.copyUint8Array(barr)
   const encoded = buffer.toBase64(barr)
   t.assert(encoded.constructor === String)
@@ -23,7 +23,25 @@ export const testRepeatBase64Encoding = tc => {
 /**
  * @param {t.TestCase} tc
  */
-export const testAnyEncoding = tc => {
+export const testRepeatHexEncoding = tc => {
+  const gen = tc.prng
+  const barr = prng.uint8Array(gen, prng.uint32(gen, 0, 47))
+  const copied = buffer.copyUint8Array(barr)
+  const encoded = buffer.toHexString(barr)
+  t.assert(encoded.constructor === String)
+  const decoded = buffer.fromHexString(encoded)
+  t.assert(decoded.constructor === Uint8Array)
+  t.assert(decoded.byteLength === barr.byteLength)
+  for (let i = 0; i < barr.length; i++) {
+    t.assert(barr[i] === decoded[i])
+  }
+  t.compare(copied, decoded)
+}
+
+/**
+ * @param {t.TestCase} _tc
+ */
+export const testAnyEncoding = _tc => {
   const obj = { val: 1, arr: [1, 2], str: '409231dtrnä' }
   const res = buffer.decodeAny(buffer.encodeAny(obj))
   t.compare(obj, res)
diff --git a/hash/sha256.js b/hash/sha256.js
new file mode 100644
index 0000000..59850c5
--- /dev/null
+++ b/hash/sha256.js
@@ -0,0 +1,180 @@
+/**
+ * @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
diff --git a/hash/sha256.test.js b/hash/sha256.test.js
new file mode 100644
index 0000000..5febe89
--- /dev/null
+++ b/hash/sha256.test.js
@@ -0,0 +1,79 @@
+import * as t from '../testing.js'
+import * as sha256 from './sha256.js'
+import * as buffer from '../buffer.js'
+import * as string from '../string.js'
+import * as prng from '../prng.js'
+import * as webcrypto from 'lib0/webcrypto'
+import * as promise from '../promise.js'
+
+/**
+ * @param {t.TestCase} _tc
+ */
+export const testSha256Basics = async _tc => {
+  /**
+   * @param {string | Uint8Array} data input data (buffer or hex encoded)
+   * @param {string} result Expected result (hex encoded)
+   */
+  const test = async (data, result) => {
+    data = typeof data === 'string' ? buffer.fromHexString(data) : data
+    const res = sha256.hash(data)
+    const resHex = buffer.toHexString(res)
+    t.assert(resHex === result)
+    const resWebcrypto = new Uint8Array(await webcrypto.subtle.digest('SHA-256', data))
+    const resWebcryptoHex = buffer.toHexString(resWebcrypto)
+    t.assert(resWebcryptoHex === result)
+  }
+
+  await test(string.encodeUtf8('abcdbcdecdefdefgefghfghighijhijkijkljklmklmnlmnomnopnopq'), '248d6a61d20638b8e5c026930c3e6039a33ce45964ff2167f6ecedd419db06c1')
+  await test(string.encodeUtf8('abc'), 'ba7816bf8f01cfea414140de5dae2223b00361a396177a9cb410ff61f20015ad')
+  await test('', 'e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855')
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testRepeatSha256Hashing = async tc => {
+  const LEN = prng.bool(tc.prng) ? prng.uint32(tc.prng, 0, 512) : prng.uint32(tc.prng, 0, 3003030)
+  console.log(LEN)
+  const data = prng.uint8Array(tc.prng, LEN)
+  const hashedCustom = sha256.hash(data)
+  const hashedWebcrypto = new Uint8Array(await webcrypto.subtle.digest('SHA-256', data))
+  t.compare(hashedCustom, hashedWebcrypto)
+}
+
+/**
+ * @param {t.TestCase} _tc
+ */
+export const testBenchmarkSha256 = async _tc => {
+  const N = 10000 // 100k
+  const BS = 530
+  /**
+   * @type {Array<Uint8Array>}
+   */
+  const datas = []
+  for (let i = 0; i < N; i++) {
+    const data = new Uint8Array(BS)
+    webcrypto.getRandomValues(data)
+    datas.push(data)
+  }
+  t.measureTime(`[webcrypto sequentially] Time to hash ${N} random values of size ${BS}`, async () => {
+    for (let i = 0; i < N; i++) {
+      await webcrypto.subtle.digest('SHA-256', datas[i])
+    }
+  })
+  t.measureTime(`[webcrypto concurrent] Time to hash ${N} random values of size ${BS}`, async () => {
+    /**
+     * @type {Array<Promise<any>>}
+     */
+    const ps = []
+    for (let i = 0; i < N; i++) {
+      ps.push(webcrypto.subtle.digest('SHA-256', datas[i]))
+    }
+    await promise.all(ps)
+  })
+  t.measureTime(`[lib0] Time to hash ${N} random values of size ${BS}`, () => {
+    for (let i = 0; i < N; i++) {
+      sha256.hash(datas[i])
+    }
+  })
+}
diff --git a/test.html b/test.html
index 8e3ce04..74061e6 100644
--- a/test.html
+++ b/test.html
@@ -32,6 +32,7 @@
   "lib0/crypto/aes-gcm": "./crypto/aes-gcm.js",
   "lib0/crypto/ecdsa": "./crypto/ecdsa.js",
   "lib0/crypto/rsa-oaep": "./crypto/rsa-oaep.js",
+  "lib0/hash/rabin": "./hash/rabin.js",
   "lib0/decoding.js": "./decoding.js",
   "lib0/dist/decoding.cjs": "./dist/decoding.cjs",
   "lib0/decoding": "./decoding.js",
diff --git a/test.js b/test.js
index 094b6d6..a5cea28 100644
--- a/test.js
+++ b/test.js
@@ -3,6 +3,7 @@ import * as array from './array.test.js'
 import * as broadcastchannel from './broadcastchannel.test.js'
 import * as crypto from './crypto.test.js'
 import * as rabin from './hash/rabin.test.js'
+import * as sha256 from './hash/sha256.test.js'
 import * as logging from './logging.test.js'
 import * as string from './string.test.js'
 import * as encoding from './encoding.test.js'
@@ -46,6 +47,7 @@ runTests({
   broadcastchannel,
   crypto,
   rabin,
+  sha256,
   logging,
   string,
   encoding,