diff --git a/crypto_secretstream.js b/crypto_secretstream.js
new file mode 100644
index 0000000..99e70a7
--- /dev/null
+++ b/crypto_secretstream.js
@@ -0,0 +1,271 @@
+/* eslint-disable camelcase */
+const assert = require('nanoassert')
+const { randombytes_buf } = require('./randombytes')
+const {
+  crypto_stream_chacha20_ietf,
+  crypto_stream_chacha20_ietf_xor,
+  crypto_stream_chacha20_ietf_xor_ic,
+  crypto_stream_chacha20_ietf_KEYBYTES
+} = require('./crypto_stream_chacha20')
+const { crypto_core_hchacha20, crypto_core_hchacha20_INPUTBYTES } = require('./internal/hchacha20')
+const Poly1305 = require('./internal/poly1305')
+const { sodium_increment, sodium_is_zero, sodium_memcmp } = require('./helpers')
+
+const crypto_onetimeauth_poly1305_BYTES = 16
+const crypto_secretstream_xchacha20poly1305_COUNTERBYTES = 4
+const crypto_secretstream_xchacha20poly1305_INONCEBYTES = 8
+const crypto_aead_xchacha20poly1305_ietf_KEYBYTES = 32
+const crypto_secretstream_xchacha20poly1305_KEYBYTES = crypto_aead_xchacha20poly1305_ietf_KEYBYTES
+const crypto_aead_xchacha20poly1305_ietf_NPUBBYTES = 24
+const crypto_secretstream_xchacha20poly1305_HEADERBYTES = crypto_aead_xchacha20poly1305_ietf_NPUBBYTES
+const crypto_aead_xchacha20poly1305_ietf_ABYTES = 16
+const crypto_secretstream_xchacha20poly1305_ABYTES = 1 + crypto_aead_xchacha20poly1305_ietf_ABYTES
+const crypto_secretstream_xchacha20poly1305_MESSAGEBYTES_MAX = Number.MAX_SAFE_INTEGER
+const crypto_aead_chacha20poly1305_ietf_MESSAGEBYTES_MAX = Number.MAX_SAFE_INTEGER
+const crypto_secretstream_xchacha20poly1305_TAGBYTES = 1
+const crypto_secretstream_xchacha20poly1305_TAG_MESSAGE = new Uint8Array([0])
+const crypto_secretstream_xchacha20poly1305_TAG_PUSH = new Uint8Array([1])
+const crypto_secretstream_xchacha20poly1305_TAG_REKEY = new Uint8Array([2])
+const crypto_secretstream_xchacha20poly1305_TAG_FINAL = new Uint8Array([crypto_secretstream_xchacha20poly1305_TAG_PUSH | crypto_secretstream_xchacha20poly1305_TAG_REKEY])
+const crypto_secretstream_xchacha20poly1305_STATEBYTES = crypto_secretstream_xchacha20poly1305_KEYBYTES +
+  crypto_secretstream_xchacha20poly1305_INONCEBYTES + crypto_secretstream_xchacha20poly1305_COUNTERBYTES + 8
+
+const KEY_OFFSET = 0
+const NONCE_OFFSET = crypto_secretstream_xchacha20poly1305_KEYBYTES
+const PAD_OFFSET = NONCE_OFFSET + crypto_secretstream_xchacha20poly1305_INONCEBYTES + crypto_secretstream_xchacha20poly1305_COUNTERBYTES
+
+const _pad0 = new Uint8Array(16)
+
+function STORE64_LE (dest, int) {
+  let mul = 1
+  let i = 0
+  dest[0] = int & 0xFF
+  while (++i < 8 && (mul *= 0x100)) {
+    dest[i] = (int / mul) & 0xFF
+  }
+}
+
+function crypto_secretstream_xchacha20poly1305_counter_reset (state) {
+  assert(state.byteLength === crypto_secretstream_xchacha20poly1305_STATEBYTES,
+    'state is should be crypto_secretstream_xchacha20poly1305_STATEBYTES long')
+
+  const nonce = state.subarray(NONCE_OFFSET, PAD_OFFSET)
+  for (let i = 0; i < crypto_secretstream_xchacha20poly1305_COUNTERBYTES; i++) {
+    nonce[i] = 0
+  }
+  nonce[0] = 1
+}
+
+function crypto_secretstream_xchacha20poly1305_keygen (k) {
+  assert(k.length === crypto_secretstream_xchacha20poly1305_KEYBYTES)
+  randombytes_buf(k)
+}
+
+function crypto_secretstream_xchacha20poly1305_init_push (state, out, key) {
+  assert(state.byteLength === crypto_secretstream_xchacha20poly1305_STATEBYTES,
+    'state is should be crypto_secretstream_xchacha20poly1305_STATEBYTES long')
+  assert(out instanceof Uint8Array && out.length === crypto_secretstream_xchacha20poly1305_HEADERBYTES, 'out not byte array of length crypto_secretstream_xchacha20poly1305_HEADERBYTES')
+  assert(key instanceof Uint8Array && key.length === crypto_secretstream_xchacha20poly1305_KEYBYTES, 'key not byte array of length crypto_secretstream_xchacha20poly1305_KEYBYTES')
+
+  const k = state.subarray(KEY_OFFSET, NONCE_OFFSET)
+  const nonce = state.subarray(NONCE_OFFSET, PAD_OFFSET)
+  const pad = state.subarray(PAD_OFFSET)
+
+  randombytes_buf(out, crypto_secretstream_xchacha20poly1305_HEADERBYTES)
+  crypto_core_hchacha20(k, out, key, null)
+  crypto_secretstream_xchacha20poly1305_counter_reset(state)
+  for (let i = 0; i < crypto_secretstream_xchacha20poly1305_INONCEBYTES; i++) {
+    nonce[i + crypto_secretstream_xchacha20poly1305_COUNTERBYTES] = out[i + crypto_core_hchacha20_INPUTBYTES]
+  }
+  pad.fill(0)
+}
+
+function crypto_secretstream_xchacha20poly1305_init_pull (state, _in, key) {
+  assert(state.byteLength === crypto_secretstream_xchacha20poly1305_STATEBYTES,
+    'state is should be crypto_secretstream_xchacha20poly1305_STATEBYTES long')
+  assert(_in instanceof Uint8Array && _in.length === crypto_secretstream_xchacha20poly1305_HEADERBYTES,
+    '_in not byte array of length crypto_secretstream_xchacha20poly1305_HEADERBYTES')
+  assert(key instanceof Uint8Array && key.length === crypto_secretstream_xchacha20poly1305_KEYBYTES,
+    'key not byte array of length crypto_secretstream_xchacha20poly1305_KEYBYTES')
+
+  const k = state.subarray(KEY_OFFSET, NONCE_OFFSET)
+  const nonce = state.subarray(NONCE_OFFSET, PAD_OFFSET)
+  const pad = state.subarray(PAD_OFFSET)
+
+  crypto_core_hchacha20(k, _in, key, null)
+  crypto_secretstream_xchacha20poly1305_counter_reset(state)
+
+  for (let i = 0; i < crypto_secretstream_xchacha20poly1305_INONCEBYTES; i++) {
+    nonce[i + crypto_secretstream_xchacha20poly1305_COUNTERBYTES] = _in[i + crypto_core_hchacha20_INPUTBYTES]
+  }
+  pad.fill(0)
+}
+
+function crypto_secretstream_xchacha20poly1305_rekey (state) {
+  assert(state.byteLength === crypto_secretstream_xchacha20poly1305_STATEBYTES,
+    'state is should be crypto_secretstream_xchacha20poly1305_STATEBYTES long')
+
+  const k = state.subarray(KEY_OFFSET, NONCE_OFFSET)
+  const nonce = state.subarray(NONCE_OFFSET, PAD_OFFSET)
+
+  const new_key_and_inonce = new Uint8Array(
+    crypto_stream_chacha20_ietf_KEYBYTES + crypto_secretstream_xchacha20poly1305_INONCEBYTES)
+  let i
+  for (i = 0; i < crypto_stream_chacha20_ietf_KEYBYTES; i++) {
+    new_key_and_inonce[i] = k[i]
+  }
+  for (i = 0; i < crypto_secretstream_xchacha20poly1305_INONCEBYTES; i++) {
+    new_key_and_inonce[crypto_stream_chacha20_ietf_KEYBYTES + i] =
+      nonce[crypto_secretstream_xchacha20poly1305_COUNTERBYTES + i]
+  }
+  crypto_stream_chacha20_ietf_xor(new_key_and_inonce, new_key_and_inonce, nonce, k)
+  for (i = 0; i < crypto_stream_chacha20_ietf_KEYBYTES; i++) {
+    k[i] = new_key_and_inonce[i]
+  }
+  for (i = 0; i < crypto_secretstream_xchacha20poly1305_INONCEBYTES; i++) {
+    nonce[crypto_secretstream_xchacha20poly1305_COUNTERBYTES + i] =
+      new_key_and_inonce[crypto_stream_chacha20_ietf_KEYBYTES + i]
+  }
+  crypto_secretstream_xchacha20poly1305_counter_reset(state)
+}
+
+function crypto_secretstream_xchacha20poly1305_push (state, out, m, ad, tag) {
+  assert(state.byteLength === crypto_secretstream_xchacha20poly1305_STATEBYTES,
+    'state is should be crypto_secretstream_xchacha20poly1305_STATEBYTES long')
+  if (!ad) ad = new Uint8Array(0)
+
+  const k = state.subarray(KEY_OFFSET, NONCE_OFFSET)
+  const nonce = state.subarray(NONCE_OFFSET, PAD_OFFSET)
+
+  const block = new Uint8Array(64)
+  const slen = new Uint8Array(8)
+
+  assert(crypto_secretstream_xchacha20poly1305_MESSAGEBYTES_MAX <=
+    crypto_aead_chacha20poly1305_ietf_MESSAGEBYTES_MAX)
+
+  crypto_stream_chacha20_ietf(block, nonce, k)
+  const poly = new Poly1305(block)
+  block.fill(0)
+
+  poly.update(ad, 0, ad.byteLength)
+  poly.update(_pad0, 0, (0x10 - ad.byteLength) & 0xf)
+
+  block[0] = tag[0]
+  crypto_stream_chacha20_ietf_xor_ic(block, block, nonce, 1, k)
+
+  poly.update(block, 0, block.byteLength)
+  out[0] = block[0]
+
+  const c = out.subarray(1, out.byteLength)
+  crypto_stream_chacha20_ietf_xor_ic(c, m, nonce, 2, k)
+  poly.update(c, 0, m.byteLength)
+  poly.update(_pad0, 0, (0x10 - block.byteLength + m.byteLength) & 0xf)
+
+  STORE64_LE(slen, ad.byteLength)
+  poly.update(slen, 0, slen.byteLength)
+  STORE64_LE(slen, block.byteLength + m.byteLength)
+  poly.update(slen, 0, slen.byteLength)
+
+  const mac = out.subarray(1 + m.byteLength, out.byteLength)
+  poly.finish(mac, 0)
+
+  assert(crypto_onetimeauth_poly1305_BYTES >=
+    crypto_secretstream_xchacha20poly1305_INONCEBYTES)
+  xor_buf(nonce.subarray(crypto_secretstream_xchacha20poly1305_COUNTERBYTES, nonce.length),
+    mac, crypto_secretstream_xchacha20poly1305_INONCEBYTES)
+  sodium_increment(nonce)
+
+  if ((tag[0] & crypto_secretstream_xchacha20poly1305_TAG_REKEY) !== 0 ||
+    sodium_is_zero(nonce.subarray(0, crypto_secretstream_xchacha20poly1305_COUNTERBYTES))) {
+    crypto_secretstream_xchacha20poly1305_rekey(state)
+  }
+
+  return crypto_secretstream_xchacha20poly1305_ABYTES + m.byteLength
+}
+
+function crypto_secretstream_xchacha20poly1305_pull (state, m, tag, _in, ad) {
+  assert(state.byteLength === crypto_secretstream_xchacha20poly1305_STATEBYTES,
+    'state is should be crypto_secretstream_xchacha20poly1305_STATEBYTES long')
+  if (!ad) ad = new Uint8Array(0)
+
+  const k = state.subarray(KEY_OFFSET, NONCE_OFFSET)
+  const nonce = state.subarray(NONCE_OFFSET, PAD_OFFSET)
+
+  const block = new Uint8Array(64)
+  const slen = new Uint8Array(8)
+  const mac = new Uint8Array(crypto_onetimeauth_poly1305_BYTES)
+
+  assert(_in.byteLength >= crypto_secretstream_xchacha20poly1305_ABYTES,
+    'ciphertext is too short.')
+
+  const mlen = _in.byteLength - crypto_secretstream_xchacha20poly1305_ABYTES
+  crypto_stream_chacha20_ietf(block, nonce, k)
+  const poly = new Poly1305(block)
+  block.fill(0) // sodium_memzero(block, sizeof block);
+
+  poly.update(ad, 0, ad.byteLength)
+  poly.update(_pad0, 0, (0x10 - ad.byteLength) & 0xf)
+
+  block.fill(0) // memset(block, 0, sizeof block);
+  block[0] = _in[0]
+  crypto_stream_chacha20_ietf_xor_ic(block, block, nonce, 1, k)
+
+  tag[0] = block[0]
+  block[0] = _in[0]
+  poly.update(block, 0, block.byteLength)
+
+  const c = _in.subarray(1, _in.length)
+  poly.update(c, 0, mlen)
+
+  poly.update(_pad0, 0, (0x10 - block.byteLength + mlen) & 0xf)
+
+  STORE64_LE(slen, ad.byteLength)
+  poly.update(slen, 0, slen.byteLength)
+  STORE64_LE(slen, block.byteLength + m.byteLength)
+  poly.update(slen, 0, slen.byteLength)
+
+  poly.finish(mac, 0)
+  const stored_mac = _in.subarray(1 + mlen, _in.length)
+
+  if (!sodium_memcmp(mac, stored_mac)) {
+    mac.fill(0)
+    throw new Error('MAC could not be verified.')
+  }
+
+  crypto_stream_chacha20_ietf_xor_ic(m, c.subarray(0, m.length), nonce, 2, k)
+  xor_buf(nonce.subarray(crypto_secretstream_xchacha20poly1305_COUNTERBYTES, nonce.length),
+    mac, crypto_secretstream_xchacha20poly1305_INONCEBYTES)
+  sodium_increment(nonce)
+
+  if ((tag & crypto_secretstream_xchacha20poly1305_TAG_REKEY) !== 0 ||
+    sodium_is_zero(nonce.subarray(0, crypto_secretstream_xchacha20poly1305_COUNTERBYTES))) {
+    crypto_secretstream_xchacha20poly1305_rekey(state)
+  }
+
+  return mlen
+}
+
+function xor_buf (out, _in, n) {
+  for (let i = 0; i < n; i++) {
+    out[i] ^= _in[i]
+  }
+}
+
+module.exports = {
+  crypto_secretstream_xchacha20poly1305_keygen,
+  crypto_secretstream_xchacha20poly1305_init_push,
+  crypto_secretstream_xchacha20poly1305_init_pull,
+  crypto_secretstream_xchacha20poly1305_rekey,
+  crypto_secretstream_xchacha20poly1305_push,
+  crypto_secretstream_xchacha20poly1305_pull,
+  crypto_secretstream_xchacha20poly1305_STATEBYTES,
+  crypto_secretstream_xchacha20poly1305_ABYTES,
+  crypto_secretstream_xchacha20poly1305_HEADERBYTES,
+  crypto_secretstream_xchacha20poly1305_KEYBYTES,
+  crypto_secretstream_xchacha20poly1305_MESSAGEBYTES_MAX,
+  crypto_secretstream_xchacha20poly1305_TAGBYTES,
+  crypto_secretstream_xchacha20poly1305_TAG_MESSAGE,
+  crypto_secretstream_xchacha20poly1305_TAG_PUSH,
+  crypto_secretstream_xchacha20poly1305_TAG_REKEY,
+  crypto_secretstream_xchacha20poly1305_TAG_FINAL
+}
diff --git a/index.js b/index.js
index 980fdd6..2f5a3f5 100644
--- a/index.js
+++ b/index.js
@@ -23,6 +23,7 @@ forward(require('./crypto_aead'))
 forward(require('./crypto_onetimeauth'))
 forward(require('./crypto_scalarmult'))
 forward(require('./crypto_secretbox'))
+forward(require('./crypto_secretstream'))
 forward(require('./crypto_shorthash'))
 forward(require('./crypto_sign'))
 forward(require('./crypto_stream'))
diff --git a/internal/hchacha20.js b/internal/hchacha20.js
new file mode 100644
index 0000000..f687b7d
--- /dev/null
+++ b/internal/hchacha20.js
@@ -0,0 +1,128 @@
+/* eslint-disable camelcase */
+const { sodium_malloc } = require('../memory')
+const assert = require('nanoassert')
+
+if (new Uint16Array([1])[0] !== 1) throw new Error('Big endian architecture is not supported.')
+
+const crypto_core_hchacha20_OUTPUTBYTES = 32
+const crypto_core_hchacha20_INPUTBYTES = 16
+const crypto_core_hchacha20_KEYBYTES = 32
+const crypto_core_hchacha20_CONSTBYTES = 16
+
+function ROTL32 (x, b) {
+  x &= 0xFFFFFFFF
+  b &= 0xFFFFFFFF
+  return (x << b) | (x >>> (32 - b))
+}
+
+function LOAD32_LE (src, offset) {
+  assert(src instanceof Uint8Array, 'src not byte array')
+  let w = src[offset]
+  w |= src[offset + 1] << 8
+  w |= src[offset + 2] << 16
+  w |= src[offset + 3] << 24
+  return w
+}
+
+function STORE32_LE (dest, int, offset) {
+  assert(dest instanceof Uint8Array, 'dest not byte array')
+  var mul = 1
+  var i = 0
+  dest[offset] = int & 0xFF // grab bottom byte
+  while (++i < 4 && (mul *= 0x100)) {
+    dest[offset + i] = (int / mul) & 0xFF
+  }
+}
+
+function QUARTERROUND (l, A, B, C, D) {
+  l[A] += l[B]
+  l[D] = ROTL32(l[D] ^ l[A], 16)
+  l[C] += l[D]
+  l[B] = ROTL32(l[B] ^ l[C], 12)
+  l[A] += l[B]
+  l[D] = ROTL32(l[D] ^ l[A], 8)
+  l[C] += l[D]
+  l[B] = ROTL32(l[B] ^ l[C], 7)
+}
+
+function crypto_core_hchacha20 (out, _in, k, c) {
+  assert(out instanceof Uint8Array && out.length === 32, 'out is not an array of 32 bytes')
+  assert(k instanceof Uint8Array && k.length === 32, 'k is not an array of 32 bytes')
+  assert(c === null || (c instanceof Uint8Array && c.length === 16), 'c is not null or an array of 16 bytes')
+
+  let i = 0
+  const x = new Uint32Array(16)
+  if (!c) {
+    x[0] = 0x61707865
+    x[1] = 0x3320646E
+    x[2] = 0x79622D32
+    x[3] = 0x6B206574
+  } else {
+    x[0] = LOAD32_LE(c, 0)
+    x[1] = LOAD32_LE(c, 4)
+    x[2] = LOAD32_LE(c, 8)
+    x[3] = LOAD32_LE(c, 12)
+  }
+  x[4] = LOAD32_LE(k, 0)
+  x[5] = LOAD32_LE(k, 4)
+  x[6] = LOAD32_LE(k, 8)
+  x[7] = LOAD32_LE(k, 12)
+  x[8] = LOAD32_LE(k, 16)
+  x[9] = LOAD32_LE(k, 20)
+  x[10] = LOAD32_LE(k, 24)
+  x[11] = LOAD32_LE(k, 28)
+  x[12] = LOAD32_LE(_in, 0)
+  x[13] = LOAD32_LE(_in, 4)
+  x[14] = LOAD32_LE(_in, 8)
+  x[15] = LOAD32_LE(_in, 12)
+
+  for (i = 0; i < 10; i++) {
+    QUARTERROUND(x, 0, 4, 8, 12)
+    QUARTERROUND(x, 1, 5, 9, 13)
+    QUARTERROUND(x, 2, 6, 10, 14)
+    QUARTERROUND(x, 3, 7, 11, 15)
+    QUARTERROUND(x, 0, 5, 10, 15)
+    QUARTERROUND(x, 1, 6, 11, 12)
+    QUARTERROUND(x, 2, 7, 8, 13)
+    QUARTERROUND(x, 3, 4, 9, 14)
+  }
+
+  STORE32_LE(out, x[0], 0)
+  STORE32_LE(out, x[1], 4)
+  STORE32_LE(out, x[2], 8)
+  STORE32_LE(out, x[3], 12)
+  STORE32_LE(out, x[12], 16)
+  STORE32_LE(out, x[13], 20)
+  STORE32_LE(out, x[14], 24)
+  STORE32_LE(out, x[15], 28)
+
+  return 0
+}
+
+function crypto_core_hchacha20_outputbytes () {
+  return crypto_core_hchacha20_OUTPUTBYTES
+}
+
+function crypto_core_hchacha20_inputbytes () {
+  return crypto_core_hchacha20_INPUTBYTES
+}
+
+function crypto_core_hchacha20_keybytes () {
+  return crypto_core_hchacha20_KEYBYTES
+}
+
+function crypto_core_hchacha20_constbytes () {
+  return crypto_core_hchacha20_CONSTBYTES
+}
+
+module.exports = {
+  crypto_core_hchacha20_INPUTBYTES,
+  LOAD32_LE,
+  STORE32_LE,
+  QUARTERROUND,
+  crypto_core_hchacha20,
+  crypto_core_hchacha20_outputbytes,
+  crypto_core_hchacha20_inputbytes,
+  crypto_core_hchacha20_keybytes,
+  crypto_core_hchacha20_constbytes
+}