Let tls-nextprotoneg use tls.lua library

Required fixes to tls lib's extensions (did not previously support
extension data)

scripts/tls-nextprotoneg.nse

@@ -5,6 +5,7 @@ local stdnse = require "stdnse"
 local table = require "table"
 local bin = require "bin"
 local os = require "os"
+local tls = require "tls"
 
 description = [[
 Enumerates a TLS server's supported protocols by using the next protocol negotiation extension.
@@ -52,40 +53,18 @@ portrule = shortport.ssl
 local client_hello = function(host, port)
     local sock, status, response, err, cli_h
 
-    -- Craft Client Hello
-    -- Content Type: Client Handshake
-    cli_h = bin.pack(">C", 0x16)
-    -- Version: TLS 1.0
-    cli_h = cli_h .. bin.pack(">S", 0x0301)
-    -- Length, fixed
-    cli_h = cli_h .. bin.pack(">S", 0x0037)
-    -- Handshake protocol
-    -- Handshake Type: Client Hello
-    cli_h = cli_h .. bin.pack(">C", 0x01)
-    -- Length, fixed
-    cli_h = cli_h .. bin.pack(">CS", 0x00, 0x0033)
-    -- Version: TLS 1.0 
-    cli_h = cli_h .. bin.pack(">S", 0x0301)
-    -- Random: epoch time
-    cli_h = cli_h .. bin.pack(">I", os.time()) 
-    -- Random: random 28 bytes
-    cli_h = cli_h .. stdnse.generate_random_string(28)
-    -- Session ID length
-    cli_h = cli_h .. bin.pack(">C", 0x00)
-    -- Cipher Suites length
-    cli_h = cli_h .. bin.pack(">S", 0x0006)
-    -- Ciphers
-    cli_h = cli_h .. bin.pack(">S", 0xc011)
-    cli_h = cli_h .. bin.pack(">S", 0x0039)
-    cli_h = cli_h .. bin.pack(">S", 0x0004)
-    -- Compression Methods length
-    cli_h = cli_h .. bin.pack(">C", 0x01)
-    -- Compression Methods: null
-    cli_h = cli_h .. bin.pack(">C", 0x00)
-    -- Extensions length
-    cli_h = cli_h .. bin.pack(">S", 0x0004)
-    -- TLS NPN Extension
-    cli_h = cli_h .. bin.pack(">I", 0x33740000)
+    cli_h = tls.client_hello({
+      ["protocol"] = "TLSv1.0",
+      ["ciphers"] = {
+        "TLS_ECDHE_RSA_WITH_RC4_128_SHA",
+        "TLS_DHE_RSA_WITH_AES_256_CBC_SHA",
+        "TLS_RSA_WITH_RC4_128_MD5",
+      },
+      ["compressors"] = {"NULL"},
+      ["extensions"] = {
+        ["next_protocol_negotiation"] = "",
+      },
+    })
 
     -- Connect to the target server
     sock = nmap.new_socket()
@@ -120,53 +99,36 @@ end
 --@args response Response to parse.
 --@return results List of found protocols.
 local check_npn = function(response)
-    local results = {}
-    local shlength, npndata, protocol
-
-    if not response then
-	stdnse.print_debug(SCRIPT_NAME .. ": Didn't get response.")
-	return results
-    end
-    -- If content type not handshake
-    if string.sub(response,1,1) ~= string.char(22) then
-	stdnse.print_debug(SCRIPT_NAME .. ": Response type not handshake.")
-	return results
-    end
-    -- If handshake protocol not server hello
-    if string.sub(response, 6, 6) ~= string.char(02) then
-	stdnse.print_debug(SCRIPT_NAME .. ": Handshake response not server hello.")
-	return results
+    local i, record = tls.record_read(response, 0)
+    if record == nil then
+      stdnse.print_debug("%s: Unknown response from server", SCRIPT_NAME)
+      return nil
     end
 
-    -- Get the server hello length
-    local _
-		_, shlength = bin.unpack(">S", response, 4)
-    local serverhello = string.sub(response, 6, 6 + shlength)
+    if record.type == "handshake" and record.body.type == "server_hello" then
+      if record.body.extensions == nil then
+        stdnse.print_debug("%s: Server does not support TLS NPN extension.", SCRIPT_NAME)
+        return nil
+      end
+      local results = {}
+      npndata = record.body.extensions["next_protocol_negotiation"]
+      if npndata == nil then
+        stdnse.print_debug("%s: Server does not support TLS NPN extension.", SCRIPT_NAME)
+        return nil
+      end
+      -- Parse data
+      i = 0
+      local protocol
+      while i < #npndata do
+        i, protocol = bin.unpack(">p", npndata, i)
+        table.insert(results, protocol)
+      end
 
-    -- If server didn't return TLS NPN extension
-    local npnextension, _ = string.find(serverhello, string.char(0x33) .. string.char(0x74))
-    if not npnextension then
-	stdnse.print_debug(SCRIPT_NAME .. ": Server doesn't support TLS NPN extension.")
-	return results
+      return results
+    else
+      stdnse.print_debug("%s: Server response was not server_hello", SCRIPT_NAME)
+      return nil
     end
-
-    -- Get NPN data length
-    local _, npnlen = bin.unpack(">S", serverhello:sub(npnextension + 2, npnextension + 3))
-    if not npnlen then
-	return results
-    end
-
-    npndata = serverhello:sub(npnextension + 4, npnextension + 4 + npnlen)
-    -- Parse data
-    local i, len = 1
-    while i < #npndata do
-	len = npndata:byte(i)
-	protocol = npndata:sub(i+1, i+len)
-	table.insert(results, protocol)
-	i = i + len + 1
-    end
-
-    return results
 end
 
 action = function(host, port)