[NSE] Modified NSE script ssl-cert.nse to support TLS negotiation

against SMTP ports that support it. Depends on Patrick's addition the
  of the reconnect_ssl method.  [Tom Sellers, David]

CHANGELOG

@@ -1,5 +1,16 @@
 # Nmap Changelog ($Id$); -*-text-*-
 
+o [NSE] Modified NSE script ssl-cert.nse to support TLS negotiation
+  against SMTP ports that support it. Depends on Patrick's addition
+  of the reconnect_ssl method.  [Tom Sellers, David]
+
+o [NSE] Added the reconnect_ssl method for sockets. We sometimes need
+  to reconnect a socket with SSL because the initial communication on 
+  the socket is done without SSL. See this thread [1] for more details. 
+  [Patrick, Tom Sellers]
+
+  [1] http://seclists.org/nmap-dev/2009/q4/3
+
 o [Zenmap] Fixed a crash that could occur when entering certain
   characters in the target entry (those whose UTF-8 encoding contains
   a byte that counts as whitespace in the Windows locale):

scripts/ssl-cert.nse

@@ -71,24 +71,38 @@ require("stdnse")
 local stringify_name
 local date_to_string
 local table_find
+local s
 
 local LIKELY_SSL_PORTS = { 443, 465, 989, 990, 992, 993, 994, 995, 587, 8443 }
+local STARTTLS_PORTS = { 25, 587 }
 
 portrule = function(host, port)
     return port.version.service_tunnel == "ssl"
-        or table_find(LIKELY_SSL_PORTS, port.number)
+        or table_find(LIKELY_SSL_PORTS, port.number) or table_find(STARTTLS_PORTS, port.number)
 end
 
 action = function(host, port)
-    local s = nmap.new_socket()
-    local status, error = s:connect(host.ip, port.number, "ssl")
-    if not status then
-        if nmap.verbosity() > 0 then
-            return error
-        else
+    s = nmap.new_socket()
+
+    if table_find(STARTTLS_PORTS, port.number) then
+        local status = starttls_negotiate(host,port)
+
+        if not status then
             return nil
         end
-    end
+    else
+        local status, error = s:connect(host.ip, port.number, "ssl")
+        
+        if not status then
+            if nmap.verbosity() > 0 then
+                return error
+            else
+                return nil
+            end
+        end    
+
+    end 
+
     local cert = s:get_ssl_certificate()
     s:close()
 
@@ -166,3 +180,67 @@ function date_to_string(date)
         return os.date("%Y-%m-%d %H:%M:%S", os.time(date))
     end
 end
+
+function starttls_negotiate(host, port)
+    -- Attempt to negotiate TLS over SMTP for services that support it
+    -- Works for SMTP (25) and SMTP Submission (587)
+
+    -- Open a standard TCP socket
+    local status, error = s:connect(host.ip, port.number, "tcp")  
+        
+    if not status then   
+        return nil
+    else 
+    
+        -- Loop until the service presents a banner to deal with server
+        -- load and timing issues.  There may be a better way to handle this.
+        local i = 0
+        repeat
+            status, resultEHLO = s:receive_lines(1)
+            i = i + 1
+        until string.match(resultEHLO, "^220") or i == 5
+
+        -- Send EHLO because the the server expects it
+        -- We are not going to check for STARTTLS in the capabilities
+        -- list, sometimes it is not advertised.
+        local query = "EHLO example.org\r\n"
+        status = s:send(query)
+        status, resultEHLO = s:receive_lines(1)
+
+        if not (string.match(resultEHLO, "^250")) then
+            stdnse.print_debug("1","%s",resultEHLO)
+            stdnse.print_debug("1","EHLO with errors or timeout.  Enable --script-trace to see what is happening.")
+            return nil
+        end
+
+        resultEHLO = ""
+        
+        -- Send STARTTLS command ask the service to start encryption    
+        local query = "STARTTLS\r\n"
+        status = s:send(query)
+        status, resultEHLO = s:receive_lines(1)
+        
+        if not (string.match(resultEHLO, "^220")) then
+            stdnse.print_debug("1","%s",resultEHLO)
+            stdnse.print_debug("1","STARTTLS failed or unavailable.  Enable --script-trace to see what is happening.")
+            
+            -- Send QUIT to clean up server side connection
+            local query = "QUIT\r\n"
+            status = s:send(query)        
+            resultEHLO = ""
+                
+            return nil
+        end
+        
+        -- Service supports STARTTLS, tell NSE start SSL negotiation
+        status, error = s:reconnect_ssl()
+        if not status then
+            stdnse.print_debug("1","Could not establish SSL session after STARTTLS command.")
+            s:close()
+            return nil
+        end 
+                
+    end    
+    -- Should have a solid TLS over SMTP session now...
+    return "Connected"
+end