## Nim-LibP2P
## Copyright (c) 2020 Status Research & Development GmbH
## Licensed under either of
##  * Apache License, version 2.0, ([LICENSE-APACHE](LICENSE-APACHE))
##  * MIT license ([LICENSE-MIT](LICENSE-MIT))
## at your option.
## This file may not be copied, modified, or distributed except according to
## those terms.

import std/[oids, strformat]
import chronos
import chronicles
import bearssl
import stew/[endians2, byteutils]
import nimcrypto/[utils, sha2, hmac]
import ../../stream/[connection, streamseq]
import ../../peerid
import ../../peerinfo
import ../../protobuf/minprotobuf
import ../../utility
import secure,
       ../../crypto/[crypto, chacha20poly1305, curve25519, hkdf]

logScope:
  topics = "noise"

const
  # https://godoc.org/github.com/libp2p/go-libp2p-noise#pkg-constants
  NoiseCodec* = "/noise"

  PayloadString = "noise-libp2p-static-key:"

  ProtocolXXName = "Noise_XX_25519_ChaChaPoly_SHA256"

  # Empty is a special value which indicates k has not yet been initialized.
  EmptyKey = default(ChaChaPolyKey)
  NonceMax = uint64.high - 1 # max is reserved
  NoiseSize = 32
  MaxPlainSize = int(uint16.high - NoiseSize - ChaChaPolyTag.len)

  HandshakeTimeout = 1.minutes

type
  KeyPair = object
    privateKey: Curve25519Key
    publicKey: Curve25519Key

  # https://noiseprotocol.org/noise.html#the-cipherstate-object
  CipherState = object
    k: ChaChaPolyKey
    n: uint64

  # https://noiseprotocol.org/noise.html#the-symmetricstate-object
  SymmetricState = object
    cs: CipherState
    ck: ChaChaPolyKey
    h: MDigest[256]

  # https://noiseprotocol.org/noise.html#the-handshakestate-object
  HandshakeState = object
    ss: SymmetricState
    s: KeyPair
    e: KeyPair
    rs: Curve25519Key
    re: Curve25519Key

  HandshakeResult = object
    cs1: CipherState
    cs2: CipherState
    remoteP2psecret: seq[byte]
    rs: Curve25519Key

  Noise* = ref object of Secure
    rng: ref BrHmacDrbgContext
    localPrivateKey: PrivateKey
    localPublicKey: seq[byte]
    noiseKeys: KeyPair
    commonPrologue: seq[byte]
    outgoing: bool

  NoiseConnection* = ref object of SecureConn
    readCs: CipherState
    writeCs: CipherState

  NoiseHandshakeError* = object of CatchableError
  NoiseDecryptTagError* = object of CatchableError
  NoiseOversizedPayloadError* = object of CatchableError
  NoiseNonceMaxError* = object of CatchableError # drop connection on purpose

# Utility

func shortLog*(conn: NoiseConnection): auto =
  if conn.isNil: "NoiseConnection(nil)"
  elif conn.peerInfo.isNil: $conn.oid
  else: &"{shortLog(conn.peerInfo.peerId)}:{conn.oid}"
chronicles.formatIt(NoiseConnection): shortLog(it)

proc genKeyPair(rng: var BrHmacDrbgContext): KeyPair =
  result.privateKey = Curve25519Key.random(rng)
  result.publicKey = result.privateKey.public()

proc hashProtocol(name: string): MDigest[256] =
  # If protocol_name is less than or equal to HASHLEN bytes in length,
  # sets h equal to protocol_name with zero bytes appended to make HASHLEN bytes.
  # Otherwise sets h = HASH(protocol_name).

  if name.len <= 32:
    result.data[0..name.high] = name.toBytes
  else:
    result = sha256.digest(name)

proc dh(priv: Curve25519Key, pub: Curve25519Key): Curve25519Key =
  result = pub
  Curve25519.mul(result, priv)

# Cipherstate

proc hasKey(cs: CipherState): bool =
  cs.k != EmptyKey

proc encryptWithAd(state: var CipherState, ad, data: openArray[byte]): seq[byte] =
  var
    tag: ChaChaPolyTag
    nonce: ChaChaPolyNonce
  nonce[4..<12] = toBytesLE(state.n)
  result = @data
  ChaChaPoly.encrypt(state.k, nonce, tag, result, ad)
  inc state.n
  if state.n > NonceMax:
    raise newException(NoiseNonceMaxError, "Noise max nonce value reached")
  result &= tag
  trace "encryptWithAd", tag = byteutils.toHex(tag), data = result.shortLog, nonce = state.n - 1

proc decryptWithAd(state: var CipherState, ad, data: openArray[byte]): seq[byte] =
  var
    tagIn = data.toOpenArray(data.len - ChaChaPolyTag.len, data.high).intoChaChaPolyTag
    tagOut: ChaChaPolyTag
    nonce: ChaChaPolyNonce
  nonce[4..<12] = toBytesLE(state.n)
  result = data[0..(data.high - ChaChaPolyTag.len)]
  ChaChaPoly.decrypt(state.k, nonce, tagOut, result, ad)
  trace "decryptWithAd", tagIn = tagIn.shortLog, tagOut = tagOut.shortLog, nonce = state.n
  if tagIn != tagOut:
    debug "decryptWithAd failed", data = shortLog(data)
    raise newException(NoiseDecryptTagError, "decryptWithAd failed tag authentication.")
  inc state.n
  if state.n > NonceMax:
    raise newException(NoiseNonceMaxError, "Noise max nonce value reached")

# Symmetricstate

proc init(_: type[SymmetricState]): SymmetricState =
  result.h = ProtocolXXName.hashProtocol
  result.ck = result.h.data.intoChaChaPolyKey
  result.cs = CipherState(k: EmptyKey)

proc mixKey(ss: var SymmetricState, ikm: ChaChaPolyKey) =
  var
    temp_keys: array[2, ChaChaPolyKey]
  sha256.hkdf(ss.ck, ikm, [], temp_keys)
  ss.ck = temp_keys[0]
  ss.cs = CipherState(k: temp_keys[1])
  trace "mixKey", key = ss.cs.k.shortLog

proc mixHash(ss: var SymmetricState; data: openArray[byte]) =
  var ctx: sha256
  ctx.init()
  ctx.update(ss.h.data)
  ctx.update(data)
  ss.h = ctx.finish()
  trace "mixHash", hash = ss.h.data.shortLog

# We might use this for other handshake patterns/tokens
proc mixKeyAndHash(ss: var SymmetricState; ikm: openArray[byte]) {.used.} =
  var
    temp_keys: array[3, ChaChaPolyKey]
  sha256.hkdf(ss.ck, ikm, [], temp_keys)
  ss.ck = temp_keys[0]
  ss.mixHash(temp_keys[1])
  ss.cs = CipherState(k: temp_keys[2])

proc encryptAndHash(ss: var SymmetricState, data: openArray[byte]): seq[byte] =
  # according to spec if key is empty leave plaintext
  if ss.cs.hasKey:
    result = ss.cs.encryptWithAd(ss.h.data, data)
  else:
    result = @data
  ss.mixHash(result)

proc decryptAndHash(ss: var SymmetricState, data: openArray[byte]): seq[byte] =
  # according to spec if key is empty leave plaintext
  if ss.cs.hasKey:
    result = ss.cs.decryptWithAd(ss.h.data, data)
  else:
    result = @data
  ss.mixHash(data)

proc split(ss: var SymmetricState): tuple[cs1, cs2: CipherState] =
  var
    temp_keys: array[2, ChaChaPolyKey]
  sha256.hkdf(ss.ck, [], [], temp_keys)
  return (CipherState(k: temp_keys[0]), CipherState(k: temp_keys[1]))

proc init(_: type[HandshakeState]): HandshakeState =
  result.ss = SymmetricState.init()

template write_e: untyped =
  trace "noise write e"
  # Sets e (which must be empty) to GENERATE_KEYPAIR(). Appends e.public_key to the buffer. Calls MixHash(e.public_key).
  hs.e = genKeyPair(p.rng[])
  msg.add hs.e.publicKey
  hs.ss.mixHash(hs.e.publicKey)

template write_s: untyped =
  trace "noise write s"
  # Appends EncryptAndHash(s.public_key) to the buffer.
  msg.add hs.ss.encryptAndHash(hs.s.publicKey)

template dh_ee: untyped =
  trace "noise dh ee"
  # Calls MixKey(DH(e, re)).
  hs.ss.mixKey(dh(hs.e.privateKey, hs.re))

template dh_es: untyped =
  trace "noise dh es"
  # Calls MixKey(DH(e, rs)) if initiator, MixKey(DH(s, re)) if responder.
  when initiator:
    hs.ss.mixKey(dh(hs.e.privateKey, hs.rs))
  else:
    hs.ss.mixKey(dh(hs.s.privateKey, hs.re))

template dh_se: untyped =
  trace "noise dh se"
  # Calls MixKey(DH(s, re)) if initiator, MixKey(DH(e, rs)) if responder.
  when initiator:
    hs.ss.mixKey(dh(hs.s.privateKey, hs.re))
  else:
    hs.ss.mixKey(dh(hs.e.privateKey, hs.rs))

# might be used for other token/handshakes
template dh_ss: untyped {.used.} =
  trace "noise dh ss"
  # Calls MixKey(DH(s, rs)).
  hs.ss.mixKey(dh(hs.s.privateKey, hs.rs))

template read_e: untyped =
  trace "noise read e", size = msg.len

  if msg.len < Curve25519Key.len:
    raise newException(NoiseHandshakeError, "Noise E, expected more data")

  # Sets re (which must be empty) to the next DHLEN bytes from the message. Calls MixHash(re.public_key).
  hs.re[0..Curve25519Key.high] = msg.toOpenArray(0, Curve25519Key.high)
  msg.consume(Curve25519Key.len)
  hs.ss.mixHash(hs.re)

template read_s: untyped =
  trace "noise read s", size = msg.len
  # Sets temp to the next DHLEN + 16 bytes of the message if HasKey() == True, or to the next DHLEN bytes otherwise.
  # Sets rs (which must be empty) to DecryptAndHash(temp).
  let
    rsLen =
      if hs.ss.cs.hasKey:
        if msg.len < Curve25519Key.len + ChaChaPolyTag.len:
          raise newException(NoiseHandshakeError, "Noise S, expected more data")
        Curve25519Key.len + ChaChaPolyTag.len
      else:
        if msg.len < Curve25519Key.len:
          raise newException(NoiseHandshakeError, "Noise S, expected more data")
        Curve25519Key.len
  hs.rs[0..Curve25519Key.high] =
    hs.ss.decryptAndHash(msg.toOpenArray(0, rsLen - 1))

  msg.consume(rsLen)

proc receiveHSMessage(sconn: Connection): Future[seq[byte]] {.async.} =
  var besize: array[2, byte]
  await sconn.readExactly(addr besize[0], besize.len).wait(HandshakeTimeout)
  let size = uint16.fromBytesBE(besize).int
  trace "receiveHSMessage", size
  if size == 0:
    return

  var buffer = newSeq[byte](size)
  await sconn.readExactly(addr buffer[0], buffer.len).wait(HandshakeTimeout)
  return buffer

proc sendHSMessage(sconn: Connection; buf: openArray[byte]): Future[void] =
  var
    lesize = buf.len.uint16
    besize = lesize.toBytesBE
    outbuf = newSeqOfCap[byte](besize.len + buf.len)
  trace "sendHSMessage", size = lesize
  outbuf &= besize
  outbuf &= buf
  sconn.write(outbuf)

proc handshakeXXOutbound(
    p: Noise, conn: Connection,
    p2pSecret: seq[byte]): Future[HandshakeResult] {.async.} =
  const initiator = true
  var
    hs = HandshakeState.init()

  try:

    hs.ss.mixHash(p.commonPrologue)
    hs.s = p.noiseKeys

    # -> e
    var msg: StreamSeq

    write_e()

    # IK might use this btw!
    msg.add hs.ss.encryptAndHash([])

    await conn.sendHSMessage(msg.data)

    # <- e, ee, s, es

    msg.assign(await conn.receiveHSMessage())

    read_e()
    dh_ee()
    read_s()
    dh_es()

    let remoteP2psecret = hs.ss.decryptAndHash(msg.data)
    msg.clear()

    # -> s, se

    write_s()
    dh_se()

    # last payload must follow the encrypted way of sending
    msg.add hs.ss.encryptAndHash(p2psecret)

    await conn.sendHSMessage(msg.data)

    let (cs1, cs2) = hs.ss.split()
    return HandshakeResult(cs1: cs1, cs2: cs2, remoteP2psecret: remoteP2psecret, rs: hs.rs)
  finally:
    burnMem(hs)

proc handshakeXXInbound(
    p: Noise, conn: Connection,
    p2pSecret: seq[byte]): Future[HandshakeResult] {.async.} =
  const initiator = false

  var
    hs = HandshakeState.init()

  try:
    hs.ss.mixHash(p.commonPrologue)
    hs.s = p.noiseKeys

    # -> e

    var msg: StreamSeq
    msg.add(await conn.receiveHSMessage())

    read_e()

    # we might use this early data one day, keeping it here for clarity
    let earlyData {.used.} = hs.ss.decryptAndHash(msg.data)

    # <- e, ee, s, es

    msg.consume(msg.len)

    write_e()
    dh_ee()
    write_s()
    dh_es()

    msg.add hs.ss.encryptAndHash(p2psecret)

    await conn.sendHSMessage(msg.data)
    msg.clear()

    # -> s, se

    msg.add(await conn.receiveHSMessage())

    read_s()
    dh_se()

    let
      remoteP2psecret = hs.ss.decryptAndHash(msg.data)
      (cs1, cs2) = hs.ss.split()
    return HandshakeResult(cs1: cs1, cs2: cs2, remoteP2psecret: remoteP2psecret, rs: hs.rs)
  finally:
    burnMem(hs)

method readMessage*(sconn: NoiseConnection): Future[seq[byte]] {.async.} =
  while true: # Discard 0-length payloads
    var besize: array[2, byte]
    await sconn.stream.readExactly(addr besize[0], besize.len)
    let size = uint16.fromBytesBE(besize).int # Cannot overflow
    trace "receiveEncryptedMessage", size, sconn
    if size > 0:
      var buffer = newSeq[byte](size)
      await sconn.stream.readExactly(addr buffer[0], buffer.len)
      return sconn.readCs.decryptWithAd([], buffer)
    else:
      trace "Received 0-length message", sconn

method write*(sconn: NoiseConnection, message: seq[byte]): Future[void] {.async.} =
  if message.len == 0:
    return

  var
    left = message.len
    offset = 0
  while left > 0:
    let
      chunkSize = if left > MaxPlainSize: MaxPlainSize else: left
      cipher = sconn.writeCs.encryptWithAd(
        [], message.toOpenArray(offset, offset + chunkSize - 1))
    left = left - chunkSize
    offset = offset + chunkSize
    var
      lesize = cipher.len.uint16
      besize = lesize.toBytesBE
      outbuf = newSeqOfCap[byte](cipher.len + 2)
    trace "sendEncryptedMessage", sconn, size = lesize, left, offset
    outbuf &= besize
    outbuf &= cipher
    await sconn.stream.write(outbuf)
    sconn.activity = true

method handshake*(p: Noise, conn: Connection, initiator: bool): Future[SecureConn] {.async.} =
  trace "Starting Noise handshake", conn, initiator

  # https://github.com/libp2p/specs/tree/master/noise#libp2p-data-in-handshake-messages
  let
    signedPayload = p.localPrivateKey.sign(
      PayloadString.toBytes & p.noiseKeys.publicKey.getBytes).tryGet()

  var
    libp2pProof = initProtoBuffer()
  libp2pProof.write(1, p.localPublicKey)
  libp2pProof.write(2, signedPayload.getBytes())
  # data field also there but not used!
  libp2pProof.finish()

  var handshakeRes =
    if initiator:
      await handshakeXXOutbound(p, conn, libp2pProof.buffer)
    else:
      await handshakeXXInbound(p, conn, libp2pProof.buffer)

  var secure = try:
    var
      remoteProof = initProtoBuffer(handshakeRes.remoteP2psecret)
      remotePubKey: PublicKey
      remotePubKeyBytes: seq[byte]
      remoteSig: Signature
      remoteSigBytes: seq[byte]

    let r1 = remoteProof.getField(1, remotePubKeyBytes)
    let r2 = remoteProof.getField(2, remoteSigBytes)
    if r1.isErr() or not(r1.get()):
      raise newException(NoiseHandshakeError, "Failed to deserialize remote public key bytes. (initiator: " & $initiator & ")")
    if r2.isErr() or not(r2.get()):
      raise newException(NoiseHandshakeError, "Failed to deserialize remote signature bytes. (initiator: " & $initiator & ")")

    if not remotePubKey.init(remotePubKeyBytes):
      raise newException(NoiseHandshakeError, "Failed to decode remote public key. (initiator: " & $initiator & ")")
    if not remoteSig.init(remoteSigBytes):
      raise newException(NoiseHandshakeError, "Failed to decode remote signature. (initiator: " & $initiator & ")")

    let verifyPayload = PayloadString.toBytes & handshakeRes.rs.getBytes
    if not remoteSig.verify(verifyPayload, remotePubKey):
      raise newException(NoiseHandshakeError, "Noise handshake signature verify failed.")
    else:
      trace "Remote signature verified", conn

    if initiator and not isNil(conn.peerInfo):
      let pid = PeerID.init(remotePubKey)
      if not conn.peerInfo.peerId.validate():
        raise newException(NoiseHandshakeError, "Failed to validate peerId.")
      if pid.isErr or pid.get() != conn.peerInfo.peerId:
        var
          failedKey: PublicKey
        discard extractPublicKey(conn.peerInfo.peerId, failedKey)
        debug "Noise handshake, peer infos don't match!",
          initiator, dealt_peer = conn,
          dealt_key = $failedKey, received_peer = $pid,
          received_key = $remotePubKey
        raise newException(NoiseHandshakeError, "Noise handshake, peer infos don't match! " & $pid & " != " & $conn.peerInfo.peerId)

    let peerInfo =
      if conn.peerInfo != nil: conn.peerInfo
      else: PeerInfo.init(remotePubKey)

    var tmp = NoiseConnection.init(conn, peerInfo, conn.observedAddr)

    if initiator:
      tmp.readCs = handshakeRes.cs2
      tmp.writeCs = handshakeRes.cs1
    else:
      tmp.readCs = handshakeRes.cs1
      tmp.writeCs = handshakeRes.cs2
    tmp
  finally:
    burnMem(handshakeRes)

  trace "Noise handshake completed!", initiator, peer = shortLog(secure.peerInfo)

  return secure

method close*(s: NoiseConnection) {.async.} =
  await procCall SecureConn(s).close()

  burnMem(s.readCs)
  burnMem(s.writeCs)

method init*(p: Noise) {.gcsafe.} =
  procCall Secure(p).init()
  p.codec = NoiseCodec

proc newNoise*(
    rng: ref BrHmacDrbgContext, privateKey: PrivateKey;
    outgoing: bool = true; commonPrologue: seq[byte] = @[]): Noise =
  result = Noise(
    rng: rng,
    outgoing: outgoing,
    localPrivateKey: privateKey,
    localPublicKey: privateKey.getKey().tryGet().getBytes().tryGet(),
    noiseKeys: genKeyPair(rng[]),
    commonPrologue: commonPrologue,
  )
  result.init()