nosey employee attack
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Thread: nosey employee attack

  1. #1
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    nosey employee attack

    Hi


    When it comes to Wireless Security, I am quite a beginner.
    Often, wireless security deals with hindering illegitimate
    users to obtain "the key".
    Fine, yet I have another problem ("nosey employee attack"[1]):


    question

    Given 1 Access Point, 2 legitimate users (A and B) with
    2 laptops (MAC addresses known). For both users the setup
    is the same (e.g. same key/passphrase ie. "the key" is known).
    If you wish there is also a RADIUS server available.


    Question: Is it possible to setup a configuration such that user B cannot read/decrypt A's traffic?


    (like this is the case in a switched wired network neglecting
    ARP poisoning, TEMPEST and co. Note that I also do not want
    to use additional mechanisms (like VPN).).


    considerations

    As far as I understand:

    • open: B always can read A's traffic (trivial)
    • WEP: B always can decrypt A's traffic (same key for RC4)
    • WPA-PSK (TKIP, with RC4): B also is able to decrypt A's traffic (same PSK, MAC known, ANonce/SNonce known -> PTK predictable[2])
    • WPA2-PSK (CCMP, with AES): seems to invoke the same problem as with TKIP/RC4.


    More interesting (and maybe the solution to the problem):
    • WPA/2-TLS/PEAP: The PSK is replaced with a client-certificate/user credentials


    Question: Assume I am in an environment with WPA/2-PEAP. I am
    connecting to the network wirelessly using 2 laptops using the
    same credentials
    . Can I decrypt the traffic flowing from the
    first laptop if sniffed on the second laptop?


    LEPS

    I read about the LEPS-Feature[3] of lancom, which allows
    to relate a MAC-address to an individual passphrase - so there
    indeed seems to be a problem?



    I hope this is not too confusing... Any help appreciated! Thanks.


    Cheers


    [1] http://www.awprofessional.com/articl...&seqNum=6&rl=1
    [2] http://www.antionline.com/showthread...592#post825592
    [3] http://www.mylancom.de/fileadmin/pro...ecurity-EN.pdf, section 9
    If the only tool you have is a hammer, you tend to see every problem as a nail.
    (Abraham Maslow, Psychologist, 1908-70)

  2. #2
    Senior Member bAgZ's Avatar
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    I haven't done wireless in a while but i seem to recall an option on my 3com wireless router where you could separate the traffic as in clients on AP cannot see each other.
    ----------------------------------------------------------------------------------------------------------
    "If I'd asked my customers what they wanted, they'd have said a faster horse." ~ Henry Ford

  3. #3
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    Hi

    I think you are referring to "client isolation". If I understand this feature
    correctly, it essentially turns the accesspoint (AP) away from "hub-behaviour":

    client isolation off: ("hub-behaviour")
    frames arriving at any port of the AP are forwarded to all other ports.

    client isolation on:
    frames arriving at the AP's wireless interface only are forward to the wired
    interface.

    Still, the wireless traffic could be sniffed.



    Essentially, I am now wondering to what extend the client certificate (TLS)
    or the user credentials (PEAP) influence the (temporal) "keys" used in the
    TKIP/CCMP-communication between the client and the AP.


    Thanks & Cheers
    If the only tool you have is a hammer, you tend to see every problem as a nail.
    (Abraham Maslow, Psychologist, 1908-70)

  4. #4
    Senior Member bAgZ's Avatar
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    As far as i understand you can always sniff traffic since it is wireless. You can have
    all of the different auth methods such as eap peap, eap tls, eap md5 which only
    help druing auth. I am not an expret on this but i think that when using Extensible
    Authentication Protocol encapsulated over Wireless LAN (EAPOWL) traffic, identity is
    not sent before the tls tunnels is up.

    But you can still sniff using passive or active attacks one solution i guess would be to
    encrypt traffic using IPSEC or soemthing like this. But don't belive me maybe you can
    check thess looks like a good resource:

    http://www.iss.net/wireless/WLAN_FAQ.php#[2.2.1]%20Wireless%20Sniffer
    or http://www.windowsecurity.com/articl...ks_Primer.html
    ----------------------------------------------------------------------------------------------------------
    "If I'd asked my customers what they wanted, they'd have said a faster horse." ~ Henry Ford

  5. #5
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    IIRC, TKIP generates a seperate key for each client based on the master key, the client's MAC and some other random salt. So, it can be sniffed, but must be decrypted. That is if I remember TKIP correctly

    /edit oops, just saw this which kind of negates what I was saying
    WPA-PSK (TKIP, with RC4): B also is able to decrypt A's traffic (same PSK, MAC known, ANonce/SNonce known -> PTK predictable[2])
    The fool doth think he is wise, but the wiseman knows himself to be a fool - Good Ole Bill Shakespeare

  6. #6
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    Hi

    Thanks for the input, both of you!

    I have found this (old) microsoft-article[1] quite interesting,
    since it discusses PEAP with MS-CHAPv2 in quite some detail.
    It confirms what you say, bAgZ , that the authentication
    only takes place after the TLS tunnel is up:


    The entire exchange is encrypted through the TLS channel created in PEAP part 1.

    This also may imply that due to the two-step initialisation, the
    random "nonces" cannot be captured since they are sent in the TLS tunnel:
    The second part is the use of EAP and a different EAP type to authenticate network access.
    (well, maybe I want to interpret it in a way I like it )


    I tend to bravely conclude that indeed, PEAP with user credentials and
    the random "nonces", which are not capturable, provide a mean to build
    unique encryption mechanisms, such that user B cannot read/encrypt
    user A's traffic even if both users use the same user credentials.
    (The possibility to enable EAP-TLS with client-side certificates is
    quite rare).


    After my visit to prague, an experiment seems to be required to confirm/deny
    these conclusions....


    Cheers

    P.s. bAgZ, of course traffic encryption using IPSec is a great way,
    but it requires for the purpose unbearable configurations on client side. Sigh.

    dmorgan, actually I confirm what you are saying: the message has to
    be decrypted, however, the key for this procedure is predictable. ANonce and SNonce
    are random, but can be sniffed since these "nonces" are sent clear-text.

    [1] http://www.microsoft.com/technet/com...uy/cg0702.mspx
    If the only tool you have is a hammer, you tend to see every problem as a nail.
    (Abraham Maslow, Psychologist, 1908-70)

  7. #7
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    yea set up a VPN server with encryption, then force both users to connect over the wireless using any VPN client that supports encryption

  8. #8
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    Hi

    As mentioned in the beginning, I did not want to go with a VPN, simply
    because I thougt that I would have to "manually" install some kind
    of VPN-client on client-side - and also to force me to think about those
    wireless protocols

    Now, I learned something new - the SSL VPN solution by Fortinet.
    All you have to do client-side is open your browser (IE), enter your
    username/password (AD, LDAP, RADIUS, but also an built-in database is
    supported) on a secure site - boom, there you go with FortiWifi:
    VPN over Wifi, with no installation client-side..

    We tested it with FortiGate - works like charm. Now we have to buy the
    FortiWifi.

    Thought, I share this experience

    Cheers
    If the only tool you have is a hammer, you tend to see every problem as a nail.
    (Abraham Maslow, Psychologist, 1908-70)

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