merging nse_openssl branch

nselib/ssh2.lua

@@ -0,0 +1,187 @@
+
+-- @author = Sven Klemm <sven@c3d2.de>
+-- @copyright See nmaps COPYING for licence
+
+module(... or "ssh2",package.seeall)
+
+require "bin"
+require "base64"
+require "openssl"
+require "stdnse"
+
+-- table holding transport layer functions
+transport = {}
+
+-- table of SSH2 constants
+local SSH2
+
+--- pack multiprecision integer for sending
+--@param bn openssl bignum 
+--@return packed multiprecision integer
+transport.pack_mpint = function( bn )
+  local bytes, packed
+  bytes = bn:num_bytes()
+  packed = bn:tobin()
+  if bytes % 8 == 0 then
+    bytes = bytes + 1
+    packed = string.char(0) .. packed
+  end
+  return bin.pack( ">IA", bytes, packed )
+end
+
+--- build a ssh2 packet
+--@param payload payload of the packet
+--@return packet to send on the wire
+transport.build = function( payload )
+  local packet_length, padding_length
+  padding_length = 8 - ( (payload:len() + 1 + 4 ) % 8 )
+  packet_length = payload:len() + padding_length + 1
+  return bin.pack( ">IcAA", packet_length, padding_length, payload, openssl.rand_pseudo_bytes( padding_length ) )
+end
+
+--- extract the payload from a received SSH2 packet
+--@param received SSH2 packet
+--@return payload of the SSH2 packet
+transport.payload = function( packet )
+  local packet_length, padding_length, payload_length, payload, offset
+  offset, packet_length, padding_length = bin.unpack( ">Ic", packet )
+  payload_length = packet_length - padding_length - 1
+  offset, payload = bin.unpack( ">A" .. payload_length, packet, offset )
+  return payload
+end
+
+--- build kexdh_init packet
+transport.kexdh_init = function( e )
+  return bin.pack( ">cA", SSH2.SSH_MSG_KEXDH_INIT, transport.pack_mpint( e ) )
+end
+
+--- build kex_init packet
+transport.kex_init = function( cookie, options )
+  options = options or {}
+  kex_algorithms = "diffie-hellman-group1-sha1"
+  host_key_algorithms = options['host_key_algorithms'] or "ssh-dss,ssh-rsa"
+  encryption_algorithms = "aes128-cbc,3des-cbc,blowfish-cbc,aes192-cbc,aes256-cbc,aes128-ctr,aes192-ctr,aes256-ctr"
+  mac_algorithms = "hmac-md5,hmac-sha1,hmac-ripemd160"
+  compression_algorithms = "none"
+  languages = ""
+
+  local payload = bin.pack( ">cAaa", SSH2.SSH_MSG_KEXINIT, cookie, kex_algorithms, host_key_algorithms )
+  payload = payload .. bin.pack( ">aa", encryption_algorithms, encryption_algorithms )
+  payload = payload .. bin.pack( ">aa", mac_algorithms, mac_algorithms )
+  payload = payload .. bin.pack( ">aa", compression_algorithms, compression_algorithms )
+  payload = payload .. bin.pack( ">aa", languages, languages )
+  payload = payload .. bin.pack( ">cI", 0, 0 )
+
+  return payload
+end
+
+--- parse kexinit package
+-- returns an empty table in case of an error
+transport.parse_kex_init = function( payload ) 
+  local _, offset, msg_code, parsed, fields, fieldname
+  parsed = {}
+
+  -- check for proper msg code
+  offset, msg_code = bin.unpack( ">c", payload )
+  if msg_code ~= SSH2.SSH_MSG_KEXINIT then return {} end
+
+  offset, parsed.cookie = bin.unpack( ">A16", payload, offset )
+
+  fields = {'kex_algorithms','server_host_key_algorithms',
+    'encryption_algorithms_client_to_server','encryption_algorithms_server_to_client',
+    'mac_algorithms_client_to_server','mac_algorithms_server_to_client',
+    'compression_algorithms_client_to_server','compression_algorithms_server_to_client',
+    'languages_client_to_server','languages_server_to_client'}
+  for _, fieldname in pairs( fields ) do
+    offset, parsed[fieldname] = bin.unpack( ">a", payload, offset )
+  end
+
+  return parsed
+end
+
+
+--- fetch SSH2 host key
+--@param host nmap host table
+--@param port nmap port table
+--@param key_type key type to fetch
+--@return table containing the key and fingerprint
+fetch_host_key = function( host, port, key_type )
+  local socket = nmap.new_socket()
+  local catch = function() socket:close() end
+  local try = nmap.new_try(catch)
+  -- oakley group 2 prime taken from rfc 2409
+  local prime = "FFFFFFFFFFFFFFFFC90FDAA22168C234C4C6628B80DC1CD129024E088A67CC74020BBEA63B139B22514A08798E3404DDEF9519B3CD3A431B302B0A6DF25F14374FE1356D6D51C245E485B576625E7EC6F44C42E9A637ED6B0BFF5CB6F406B7EDEE386BFB5A899FA5AE9F24117C4B1FE649286651ECE65381FFFFFFFFFFFFFFFF"
+
+  try(socket:connect(host.ip, port.number))
+  -- fetch banner
+  try(socket:receive_lines(1))
+  -- send our banner
+  try(socket:send("SSH-2.0-Nmap-SSH2-Hostkey\r\n"))
+
+  local cookie = openssl.rand_bytes( 16 )
+  local packet = transport.build( transport.kex_init( cookie, {host_key_algorithms=key_type} ) )
+  try(socket:send( packet ))
+
+  local kex_init = try(socket:receive_bytes(1))
+  kex_init = transport.parse_kex_init( transport.payload( kex_init ) )
+
+  if not tostring(kex_init.server_host_key_algorithms):find( key_type, 1, true ) then
+    -- server does not support host key type
+    stdnse.print_debug( 2, "Hostkey type '%s' not supported by server.", key_type )
+    return
+  end
+
+  local e, g, x, p
+  -- e = g^x mod p
+  g = openssl.bignum_dec2bn( "2" )
+  p = openssl.bignum_hex2bn( prime )
+  x = openssl.bignum_pseudo_rand( 1024 )
+  e = openssl.bignum_mod_exp( g, x, p )
+
+  packet = transport.build( transport.kexdh_init( e ) )
+  try(socket:send( packet ))
+
+  kexdh_reply = try(socket:receive_bytes(1))
+  kexdh_reply = transport.payload( kexdh_reply )
+  -- check for proper msg code
+  if kexdh_reply:byte(1) ~= SSH2.SSH_MSG_KEXDH_REPLY then
+    return
+  end
+
+  local _,public_host_key,bits,algorithm
+  _, _, public_host_key = bin.unpack( ">ca", kexdh_reply )
+
+  if key_type == 'ssh-dss' then
+    algorithm = "DSA"
+    local p
+    _, _, p = bin.unpack( ">aa", public_host_key )
+    bits = openssl.bignum_bin2bn( p ):num_bits()
+  elseif key_type == 'ssh-rsa' then
+    algorithm = "RSA"
+    local n
+    _, _, _, n = bin.unpack( ">aaa", public_host_key )
+    bits = openssl.bignum_bin2bn( n ):num_bits()
+  else
+    stdnse.print_debug( "Unsupported key type: %s", key_type )
+  end
+
+  return { key=public_host_key, key_type=key_type, fp_input=public_host_key, bits=bits,
+           full_key=('%s %s'):format(key_type,base64.enc(public_host_key)),
+           algorithm=algorithm, fingerprint=openssl.md5(public_host_key) }
+end
+
+-- constants
+
+SSH2 = {
+  SSH_MSG_DISCONNECT = 1,
+  SSH_MSG_IGNORE = 2,
+  SSH_MSG_UNIMPLEMENTED = 3,
+  SSH_MSG_DEBUG = 4,
+  SSH_MSG_SERVICE_REQUEST = 5,
+  SSH_MSG_SERVICE_ACCEPT = 6,
+  SSH_MSG_KEXINIT = 20,
+  SSH_MSG_NEWKEYS = 21,
+  SSH_MSG_KEXDH_INIT = 30,
+  SSH_MSG_KEXDH_REPLY = 31,
+}
+