Text 3441, 61 rader
Skriven 2005-04-07 17:01:12 av Mike '/m' (1:379/45)
   Kommentar till text 3421 av Gary Britt (1:379/45)
Ärende: Re: Wireless Network Security Questions
===============================================
From: Mike '/m' <mike@barkto.com>

On Wed, 6 Apr 2005 15:29:49 -0400, "Gary Britt" <zotu@nospamforme.com> wrote:

>I have done two security things.  I disabled broadcast of the SSID,

http://www.symbol.com/products/wireless/broadcasting_ssid_.html

===
Why ‘Not Broadcasting the SSID' is not a Form of Security


Summary

This paper discusses an aspect of the 802.11 protocols that some manufacturers
have altered and marketed as a security feature. The feature is the removal of
the SSID (also known as the NetID and ESSID) in a particular frame type called
a beacon. It is this that is being marketed as a security feature. This paper
explains the technical detail of the beacon and why in reality there is no gain
in security. There is no gain since there are other frames that require the
SSID to be present in clear plain text.


...The beacon frame (shown in the next diagram) is transmitted periodically to
allow stations to locate and identify a BSS. The information in a beacon frame
allows a mobile unit to locate the BSS at any time in the future. The beacon
frame also conveys information to mobile units about frames that may be
buffered during times of low power operation. The beacon frame includes fixed
fields such as timestamp, beacon interval, and capability information. The
timestamp is a 64 bit field that contains the value of the station's
synchronization timer at the time that the frame was transmitted. The beacon
interval is the period, measured in ‘time units' of 1024 microseconds, of
beacon transmissions. The beacon interval is a 16 bit field. The capability
information field is a 16 bit field that identifies the capabilities of the
station.

The information elements in a beacon frame are the SSID, supported rates, PHY
parameter sets (FH and DS), optional CF (Contention Free) parameter set,
optional IBSS parameter set, and an optional TIM (Traffic Indication Map)

The probe request frame is transmitted by a mobile station attempting to
quickly locate an IEEE 802.11 WLAN. It may be used to locate a WLAN with a
particular SSID or to locate any WLAN. The probe request contains two
information elements, the SSID and the supported rates. The effect of receiving
a probe request is to cause a station to respond with a probe response, if the
receiver was the last station in the BSS to transmit a beacon frame. In an
infrastructure BSS, the AP will always respond to the probe requests. In an
IBSS, the mobile unit that sent the latest beacon will respond.

The probe response frame contains nearly all the same information as a beacon
frame. The probe response includes the timestamp, beacon interval, and
capability information fixed fields. It also includes the SSID, supported
rates, one or more PHY parameter sets (FH and DS), the optional CF parameter
set, and the optional IBSS parameter set. This is all in clear text whatever
the encryption method being used....
===

  /m

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