ssh.lua

local openssl = require('openssl')
local tcp = require('coro-tcp')
local table = require('table')
local bit = require('bit')

local LOCAL_VERSION = "SSH-2.0-LUVIT-1"
local SUPPORTED_HOSTKEY_ALGOS = "ssh-rsa"
local SUPPORTED_MAC_MODE = "hmac-sha2-256"
local SUPPORTED_CIPHER_MODE = "aes256-ctr"
local SUPPORTED_KEX_ALGOS = "ecdh-sha2-nistp256"
local SUPPORTED_COMPRESSION_MODE = "none"

local function parseUint32(buffer, offset)
  offset = offset or 1
  local num = bit.bor(
      bit.lshift(string.byte(buffer, offset), 24),
      bit.lshift(string.byte(buffer, offset + 1), 16),
      bit.lshift(string.byte(buffer, offset + 2), 8),
      string.byte(buffer, offset + 3)
    )
  return num, 4
end

local function writeUint32(num)
  return table.concat({
    string.char(bit.band(bit.rshift(num, 24), 0xff)),
    string.char(bit.band(bit.rshift(num, 16), 0xff)),
    string.char(bit.band(bit.rshift(num, 8), 0xff)),
    string.char(bit.band(num, 0xff)),
  })
end

exports.client = function()
  local rawRead, rawWrite, socket
  local buffer = ''

  local function exchangeVersion()
    buffer = buffer .. rawRead()
    local idx = buffer:find('\n')
    if idx == -1 then return end
    buffer = buffer:sub(idx + 1)
    rawWrite(LOCAL_VERSION .. '\r\n')
  end

  local padLengthMultiple = 16

  local function send(payload)
    payload = table.concat(payload)
    local pktlen = #payload + 9
    pktlen = pktlen + ((padLengthMultiple - 1) * pktlen) % padLengthMultiple
    local padLen = pktlen - #payload - 5
    local frame = {
      writeUint32(pktlen - 4),
      string.char(padLen),
      payload,
      openssl.random(padLen)
    }
    rawWrite(table.concat(frame))
  end

  local function readKex()
    local length, offsetAdd, offset, pktLen
    buffer = buffer .. rawRead()
    if #buffer < 20 then return end
    pktLen, offsetAdd = parseUint32(buffer)
    while #buffer < pktLen - 4 do
      buffer = buffer.. rawRead()
    end
    local padLen = string.byte(buffer, 5)
    local type = string.byte(buffer, 6)
    local cookie = string.sub(buffer, 7, 22)
    length, offsetAdd = parseUint32(buffer, 23)
    offset = 23 + offsetAdd + length - 1
    local kexStr = buffer:sub(27, offset)
    offset = offset + 1
    length, offsetAdd = parseUint32(buffer, offset)
    offset = offset + offsetAdd
    local keyFormats = buffer:sub(offset, offset + length - 1)
    offset = offset + length

    length, offsetAdd = parseUint32(buffer, offset)
    offset = offset + offsetAdd
    local clientServerCiphers = buffer:sub(offset, offset + length - 1)
    offset = offset + length

    length, offsetAdd = parseUint32(buffer, offset)
    offset = offset + offsetAdd
    local serverClientCiphers = buffer:sub(offset, offset + length - 1)
    offset = offset + length

    length, offsetAdd = parseUint32(buffer, offset)
    offset = offset + offsetAdd
    local clientServerHMAC = buffer:sub(offset, offset + length - 1)
    offset = offset + length

    length, offsetAdd = parseUint32(buffer, offset)
    offset = offset + offsetAdd
    local serverClientHMAC = buffer:sub(offset, offset + length - 1)
    offset = offset + length

    length, offsetAdd = parseUint32(buffer, offset)
    offset = offset + offsetAdd
    local clientServerCompression = buffer:sub(offset, offset + length - 1)
    offset = offset + length

    length, offsetAdd = parseUint32(buffer, offset)
    offset = offset + offsetAdd
    local serverClientCompression = buffer:sub(offset, offset + length - 1)

    buffer = buffer:sub(pktLen + 5)

    p('type', type)
    p('cookie', cookie)
    p('kexStr', kexStr)
    p('keyFormats', keyFormats)
    p('clientServerCiphers', clientServerCiphers)
    p('serverClientCiphers', serverClientCiphers)
    p('clientServerHMAC', clientServerHMAC)
    p('serverClientHMAC', serverClientHMAC)
    p('clientServerCompression', clientServerCompression)
    p('serverClientCompression', serverClientCompression)

    local msg = {
      string.char(20),
      openssl.random(16),
      writeUint32(#SUPPORTED_KEX_ALGOS), SUPPORTED_KEX_ALGOS, -- kexlist
      writeUint32(#SUPPORTED_HOSTKEY_ALGOS), SUPPORTED_HOSTKEY_ALGOS, -- server host key algos
      writeUint32(#SUPPORTED_CIPHER_MODE), SUPPORTED_CIPHER_MODE, -- cipher list
      writeUint32(#SUPPORTED_CIPHER_MODE), SUPPORTED_CIPHER_MODE, -- cipher list
      writeUint32(#SUPPORTED_MAC_MODE), SUPPORTED_MAC_MODE, -- hmac
      writeUint32(#SUPPORTED_MAC_MODE), SUPPORTED_MAC_MODE, -- hmac
      writeUint32(#SUPPORTED_COMPRESSION_MODE), SUPPORTED_COMPRESSION_MODE, -- compress
      writeUint32(#SUPPORTED_COMPRESSION_MODE), SUPPORTED_COMPRESSION_MODE, -- compress
      writeUint32(0), "", -- languages
      writeUint32(0), "", -- languages
      string.rep(string.char(0), 5) -- reserve
    }

    send(msg)
  end

  local function connect(options)
    rawRead, rawWrite, socket = tcp.connect(options.host, options.port)
    exchangeVersion()
    readKex()
  end

  return {
    connect = connect
  }
end