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Public Access 'Blackspots'
WeakGeek writes "Unstrung has a story talking about a security issue with the combining of 802.11 and GSM/GPRS networks. Seems that 802.11b hotspots provide hackers with an easy way to grab user information from the wide-area network itself.
Back when GSM was being defined, standards were designed to only authenticate the details held on the SIM card in a user's device before starting a session on the network. The user's device doesn't in turn check the credentials of the network. Fake a network, get data.
Of course, the linked to story seems to be a 'viral' advertisement for a product that fixes this, but I still thought it interesting enough to share."
02.21.03
CANNES, France -- 3GSM Congress -- There's a big problem with connecting public wireless LAN access points to GSM/GPRS cellular networks, according to SIM card vendor SchulmbergerSema. 802.11b hotspots provide hackers with an easy way to grab user information from the wide-area network itself, the company tells Unstrung.
The heart of the problem is that when the GSM standard was being defined back in the late 80s, no one imagined that a hacker could set up his own wireless network to gain access to an operator's network and the user data therein. Therefore, GSM networks only authenticate the details held on the SIM card in a user's device before starting a session on the network. The user's device doesn't check the credentials of the network it is attempting to access.
This was fine before the advent of wireless LAN. But now for a minimal outlay anyone can own a wireless network.
At the same time, vendors and operators are starting to use SIM card-based authentication front-end systems for public wireless LAN networks, which allow them to link the user back to the home location register (HLR) database on the GSM network and thus manage and bill a subscriber on the WLAN network in the same way as they would on the wide-area network.
This all adds up to networks that could be vulnerable to hacker attacks, according to Schlumberger.
Hackers can set up "rogue" hotspots that users will access in the belief they are on the genuine public wireless LAN network. Once users are on the fake network, it is easy for the hacker to access data held on the device via the 802.11 connection (see WLAN: The Four S's and this paper for more on the insecurity of wireless LAN). Hackers can then break into the SIM software on the user's device and get the codes held there. They can then use that information to fool the GSM authentication system and thus gain access to the network.
Schlumberger say that this won't be a problem once UMTS networks are available, because the 3G standard ensures what's known as "mutual authentication" -- the network authenticates a user device, and the device confirms that it is actually on a valid network before the session can proceed.
However, for public wireless LAN implementations that will connect to backend systems on GSM and GPRS networks, Schlumberger has developed a SIM card-based system (surprise!) that enables mutual authentication between the device and networks that are accessed via the gateway of public wireless LAN hotspots. The mutual authentication takes place via algorithms on the card itself rather than in SIM card software on the device.
Schlumberger is showing a system at the 3GSM congress that uses a separate smartcard and reader plugged into a WLAN-enabled laptop. However, the firm says that the smartcard and radio could be integrated into one PCMCIA card, much in the way that Nokia Corp. (NYSE: NOK - message board) has done.
Orange France is currently testing Schlumberger's security system. Schlumberger expects that operators will start to roll it out before the end of this year.
-- Dan Jones, Senior Editor, Unstrung
http://www.unstrung.com
The answer is quite simple actually. If the phone could support a protocol with a cheaper infrastructure, then implementing the protocol might not be a bad idea. Say for example that you have an A band PCS network (1850->1945 MHz). The network has great outdoor coverage, but the in-building penetration at PCS frequencies is weak. A large buisness customer wants better coverage inside their offce, but doesn't want to foot the bill for a new $70,000+ base station, never mind trying to get FCC/FAA approval or a lease. Instead, using the network infrastructure that already exists inside the building you add 802.11 access points in places where coverage is weak. Voila, you've managed to solve the problem for probably less that $5,000. There are of course problems with smooth handovers between the 802.11 part of the network and the GSM part of the network, but that's a whole other kettle of fish.
No, WEP stands for Wireless Equivalent Privacy, and it certainly has nothing to do with good encryption (uses RC4). What the WEP tries to (poorly) gaurantee is that clients are authenticated with the access point, server, whatever. Unfortunately, it is a one-way authentication that only validates the client, not the access point or server. What that means is that if you get a rogue access point with a bigger signal than the legitimate access point, the client will authenticate with the rogue access point, giving away passwords, encryption keys, etc. Throw in the fact that most wireless networks use shared keys, and you have just set yourself up for a security disaster. SSL gateway will not really help you if you have a man in the middle attack. If the man in the middle can grab the authentication key, it can masquerade as a legitimate user and possibly find out even more great things. If you want more info, check out "Wireless Network Security" published by the National Institute of Standards and Technology and the Department of Commerce. As far as encryption goes, WEP even gives away 24 bits of the encryption key with the IV (Initialization Vector). If you want a good list of the problems with wireless, check out section 3.3.2 of the document I mentioned. If you'd like a checklist of things you can do to lessen your security risks with wireless, check out sections 3.8 and 3.9. Of course, they include things like eye scanners and fingerprint scanners to even access a room with wireless capabilities, but most of those recommendations can be implemented by small to medium businesses with small amounts of technology capital. Thank you for your time, Quadgoatboy
The scenario is one where GSM operators use 802.11 to provide data-infill on their GSM networks, and reuse the GSM authentication mechanism over 802.11 to control access. The article is correct to point out that it would be relatively easy for someone to setup an 802.11 access point which pretends to belong to a GSM operator and requests GSM authentication information from connecting devices.
However, this shouldn't be too big a problem. The GSM authentication mechanism is based on a shared secret key which is written in to the SIM card in a way that SHOULD be read-only. Once its written the key is used by the SIM to calculate a response to a challenge sent from the network. This authentication algorithm is chosen by the network operator, and should be a one way function (ie you can't analyse the challenge/responses to get the secret key). Therefore, the hacker with a false network could get a set of valid responses to a set of challenges, but if the authentication algorithm is correct he can't use this data to get the secret key and clone the SIM.
The only comment I would make is that flaws have been discovered in the authentication algorithms used by some networks which potentially makes it possible to find the secret key if you have enough challenge/response data. However these algorithms are being replaced, and the computation is still quite heavy.
To summarise: fake networks attacks aren't new. Using 802.11 just makes it easier. Its best to suppress fake networks by mutual autentication, but even if you don't do this it should still be impossible for the fake network to get enough data to clone a mobile. The main problem with fake networks is that they can intercept the content of communications very easily.