Steve Gibson weighs in on WPA-PSK keys

Steve Gibson weighs in on WPA-PSK keys

Summary: Brute forcing cryptographic keys is only interesting from a top secret or academic standpoint. Brute forcing a random 8 character alphanumeric WPA-PSK key for a home is a fool's errand because there are infinitely cheaper and easier ways to penetrate a home network by some other means.

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TOPICS: Wi-Fi
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When I got an email from a gentleman pointing me to a link where the great Steve Gibson weighed in on my blog about sufficient key lengths for WPA-PSK keys, I knew I had to brace myself for a good old fashion can of WA.  Little did I know that my blog from editor's hell which required four edits had an infectious quality to it that even proved Steve Gibson a mortal.  In any case, it's three of my mistakes compared to Gibson's one so it's not like I have anything to gloat about.  But in all seriousness, I have the utmost respect for Mr. Gibson and I'm going to address some of his points.

Gibson first questions my premise that WPA-PSK pass phrase cracking programs check possible WPA-PSK keys at approximately 100 keys per second on a fast PC and states that he could probably make it significantly faster.  While I have no doubt that Gibson can deliver on such a promise because of his superb programming skills in raw assembler, the 100 keys per second figure is based on a publicly available tool (by Joshua Wright) which happens to be the fastest WPA-PSK cracking tool I know of.

Then Gibson went on to say (which he later took back) that it would be possible to generate a pre-computed master table that makes it extremely fast to search for weak WPA-PSK keys.  In a subsequent post soon after his original post, Gibson corrected himself and stated that such a pre-computed master table was not possible due to the solid design of the WPA-PSK standard.  To clarify the situation further, Joshua Wright did point out to me that the WPA-PSK uses the SSID as the SALT to prevent the ability to generate pre-computed tables.  What this means is that it is possible to generate a pre-computed table for a given SSID of a Wireless LAN which means it's a good idea to throw in some randomness for the SSID name you give to your Wireless LAN.  Furthermore, pre-computing the fast cracking table takes a just as long (100 keys per second) to compute in the first place unless you start using some of the newer dual-core processors, expensive hardware floating point accelerators, a massive bank of PCs (perhaps hijacked as David Berlind pointed out), or if Gibson writes an Assembler optimized version of a WPA-PSK cracker.  But even with these additional factors thrown in, bumping up the WPA-PSK pass phrase from 8 alphanumeric characters to 10 alphanumeric characters with a few capitol letters thrown in will make the cracking exercise almost about 298 thousand times more difficult.

Now this debate in WPA-PSK key selection is definitely interesting, but it really wasn't the point of my original blog.  My point was not to make a recommendation for a WPA-PSK key that was technically "unbreakable", but to make a recommendation for a key that was very infeasible to break for a home network.  Brute forcing cryptographic keys is only interesting from a top secret or academic standpoint.  Brute forcing a random 8 character alphanumeric WPA-PSK key for a home is a fool's errand because there are infinitely cheaper and easier ways to penetrate a home network by some other means.

The real reason for my blog was to address the pathetic penetration of WPA in the home.  If you look at the results from that poll, you'll see that most people are still using WEP while many others were opting for one of the myths in Wireless LAN security.  My purpose was to make WPA-PSK reasonably safe while trying not to intimidate the end users.  Microsoft even offers this tool for automatically setting up a USB key with a long random key and an automatic secure wireless profile installer.  That's great if you have a USB key available, but that may not always be an option.  There are many other ways which are definitely more sound from a cryptographic standpoint, but what good is it if people don't want to use it because it's too hard?  The real challenge is to get people to use WPA at all.

Topic: Wi-Fi

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18 comments
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  • Hard knocks for little profit...

    sounds like a good standard for home security to me. Home users need to do threat assessment similar to the big boys. We think about what we have to protect and invest in an appropriate level of security. I'm not weighing in on your specific technical arguments because I haven't been following them.

    PS: Just to distract you... or provide grist for a new blog, have you noticed that Tivo 2 machines don't support WPA? As consumer electronics tries to 'converge' with computer networks, it sure would be nice if they kept up with the security standards.
    palmwarrior
    • But the profits could be more...

      with general public availability of password cracking tools along with worm code to create botnets, the effort could be commensurate with the profit depending on who you were targeting. Suppose for example you could pick up the WiFi signal from the house belonging to the CEO of a public company. Or what about small to medium businesses that have opted for WPA-based security in lieu of one of the more industrial strength (but more difficult to manage) options? I think there is more at risk here than what originally meets the eye.

      Also, another question, with Weschester, NY passing local laws that make it an offense to run an unsecured WiFi network, who gets to decide what is secured? For example, if I run WEP encryption which is, technically speaking is for security, but practically speaking, doesn't work, am I in violation of the law or not? Easy for us to answer but have you ever seen what happens when politicians, law enforcement, and judicial systems get involved in technological hairsplitting?

      db
      dberlind
      • AFIK

        that law hasn't been passed in NY yet. Heck, it hasn't even been formally proposed. It's in the draft stage. Please correct me if I'm wrong.

        Not that it isn't a ridiculous notion, anyway. How does one enforce that, how does one even check complaince without attempting unauthorized access to the network, which may be illegal?
        Real World
      • Westchester and WPA cracking

        If it were a CEO, I would consider that a high risk target. In that case, WPA Enterprise mode with a minimum of PEAP authentication would be much more appropriate which isn't susceptible to offline cracking at all. Enterprise users (not just CEOs) should be given a firewall/routers/switch/AP device like the Cisco 851W that can be partitioned in to a non-secure network for the home along with a secure setup for the enterprise that has a seamless VPN tunnel to the office.

        As for Westchester, those bozos might be rethinking their proposed law because clearly they don't know what they're talking about and they were getting tons of complaints. I can't say if it's the government's place to tell home or hotspots if they have to use a secure setup or not because that's a legal issue, what I can tell you that what Westchester is proposing (in its current state) will actually deliver less security.
        george_ou
        • Guessing.

          The complaints in Westchester were probably from people who didn't want to go to the trouble and expense of securing their systems. Computers cost enough without having to worry about defrag or any other extraneous issues.

          And I also suspect the kind of testing they were thinking about was sitting on a street with a laptop, which provided the information that started this incident.

          You wrote:
          As for Westchester, those bozos might be rethinking their proposed law because clearly they don't know what they're talking about and they were getting tons of complaints. I can't say if it's the government's place to tell home or hotspots if they have to use a secure setup or not because that's a legal issue, what I can tell you that what Westchester is proposing (in its current state) will actually deliver less security.

          Less than what? Presuming there's no attempt at security in many homes now, how would the situation become worse?
          Anton Philidor
          • Please read the original blog on Westchester

            Anton, it sounds like you didn't read my blog on Westchester. "http://blogs.zdnet.com/Ou/?p=125"

            They're actually going to tell (mandate) people to deploy a "firewall" (which they don't clearly define from an architecture or ACL standpoint) RATHER than good solid Wi-Fi crypto. That is just plain stupid.

            Please read the original blog and I'd be happy to discuss it with you.
            george_ou
          • I did.

            Here are a couple of quotes from the town official's statements:

            Last week, a team from the Department of Information Technology performed the same survey and came across 248 wireless hot spots in less than a half an hour of driving down Westchester Avenue and Main Street in White Plains. Out of those, 120, or almost half, lacked any visible security at all. Many users marked themselves as easy targets by failing to change the network?s default name from ?default? to something unique.

            They used a laptop.
            This was the sort of inspection I thought would be the model.

            And:
            ?Wi-Fi is a wonderful technology if used wisely,? said Jacknis. ?Protecting your computer involves little to no cost. Setting up a Wi-Fi network with basic security takes just a few minutes and there are available free or low-cost personal firewalls to stop intruders from gaining access to your personal computer.?

            That sounds a software firewall on a pc to me.

            And here's your comment apparently confirming that homes in addition to businesses are being targetted:

            As for Westchester, those bozos might be rethinking their proposed law because clearly they don't know what they're talking about and they were getting tons of complaints. I can't say if it's the government's place to tell home or hotspots if they have to use a secure setup or not because that's a legal issue, what I can tell you that what Westchester is proposing (in its current state) will actually deliver less security.

            Notice the "home or hotspots".

            And if you once get homes into the mix, then the public definitely will begin to complain about legally demanded maintenance.

            So I'm not sure what I'm missing. Which is probably why I missed it.
            Anton Philidor
          • I think you just read the news story and not my blog

            "That sounds a software firewall on a pc to me"

            No, I read their proposed law. They were talking about some sort of gateway firewall but they were not clear.

            Did you read my blog or the news story?

            I'm talking about my blog: http://blogs.zdnet.com/Ou/?p=125

            "Second, this law would even pertain to open Wi-Fi access in a places like coffee shops where no servers, cash register or sensitive data is present. The law even applies to businesses that already run secure wireless LANs using good encryption and authentication. If a business wants to run internal firewalls or not on a SECURE NETWORK, that's their business and no one else's. Hardening servers and running secure authentication protocols is much more important on an internal network than running some extra firewalls. Using this "logic", why not mandate internal firewalls for all wired and wireless networks regardless of whether they are secure or not?"

            That's the insanity I'm talking about. I'm still in the process of talking with them.
            george_ou
          • Ah, I read in too much and too little.

            The last sentence of the quote from your blog:

            Using this "logic", why not mandate internal firewalls for all wired and wireless networks regardless of whether they are secure or not?"

            Having already decided they were thinking about ZoneAlarm Free for all, I took this as your confirmation, mixed with disbelief.


            You're thinking about what could sensibly be mandated, and for businesses only.

            I wasn't giving them that much credit. And I included homes.

            Glad you're in touch with them. Guessing may produce reasonable interpretations, but reality is better.
            Anton Philidor
          • If they're really that serious about this initiative

            first, they need specific definitions. Second, they should make it part of the building code, and use a similar process for punishing violators. Building codes aren't negotiable. Compliance is not optional. And professionals who do the work for you are then accountable for not meeting the code.
            Real World
    • Yes, I've been slamming Sony for their PSP

      As far as I'm concerned, this is one area that should be fixed now or be opened to a class action. There is no excuse to be heading in to 2006 nearly 3 years after the arrival of the WPA standard to still be selling WEP only devices. They do this because they think they can get away with it.

      If Sony tries to do this with their PS3, I'll be all over them again.
      george_ou
  • Help your neighbors!

    "The real reason for my blog was to address the pathetic penetration of WPA in the home. If you look at the results from that poll, you'll see that most people are still using WEP while many others were opting for one of myths in Wireless LAN security."

    So, here's the ethical question of the day. Do we - as knowledgable ITers - help our neighbors with choosing a setting up good wireless security.

    In my opinion - yes, we should. I'm not fond of free work, but ethically I can't let my neighbors use technology that could place them in harms way. Granted, the odds of a death or serious physical harm are slim to none, but the odds of serious financial harm are too great to ignore.

    My 2 cents.
    Chad Strunk
    • I help more by spreading the right information

      nt
      george_ou
  • Of course...

    ...if everyone used secure networks, I wouldn't have had internet access from my apartment for the 7 days it took for Adelphia to set it up.

    Was I riding for free on a neighbors internet connection? Never. I'm offended at the thought.

    I see your point about the WPA key length, though. Like you said, the issue is not whether it can be broken. The issue is whether a high enough threshold of pain has been created to deter people trying to break into HOME NETWORKS. If this was the Pentagon, it would be a different issue entirely (and they probably shouldn't be using WiFi in the first place). Joe the script reader for Fox, though, is less of a target.
    John Carroll
    • This is why they call it WPA home

      There is WPA Enterprise which is not susceptible to offline key cracking. If this were a pentagon network, they should be using battle field grade WPA2 AES encryption along with EAP-TLS authentication which required FIPS certified cryptographic tokens. But I'm just talking about grandma?s house :). Like I said, even it is technically possible to break WPA-PSK with 8 random alphanumeric characters; it would be the least feasible way of breaking in to a home network.
      george_ou
    • You were 'riding for free'

      and it's probably illegal. It is at least unethical, and it's interesting that a Microsoft employee publically chuckles at this type of exploit. (I know you're not speaking for the company here.)
      Real World
  • Why aren't homes using WPA? That's easy!

    Answer: WiFi vendors are still recommending WEP!

    I just activated the WiFi services on a Qwest-owned Actiontec DSL modem with built-in 802.11b/g. The CURRENT Actiontec manual and Qwest's web pages give WEP examples for enabling security, but don't even explain how to configure WPA! I had to find a PDF from another DSL service that also uses the Actiontec series to figure out how to enable WPA.

    If you follow the Actiontec installation guide, you're going to wind up with WEP (in)security. Period.
    dhdoyle@...
    • Why I Don't Use WPA

      i don't use wpa because although i have an all d-link network, the moment i turn on wpa the network goes down and stays down until i re-establish wep. i've searched the net for why this happens, and posted it on various "talk backs" when the subject comes up, but no one has ever provided me an answer that solves the problem.

      mark d.
      markdoiron