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Wireless Networking Hardware

New Wireless Security Standard Has Old Problem? 249

Posted by simoniker
from the it's-always-something dept.
eggboard writes "Wireless security expert Robert Moskowitz, who sits on IEEE and IETF committees on that subject, sent me a short paper on a glaring weakness in the Wi-Fi Protected Access (WPA) protocol that's replacing the weak and broken WEP system well discussed here at Slashdot. His paper, which I've posted here, proves definitively that while WPA itself remains robust and secure, the interface for choosing consumer passwords makes it simple to snarf a tiny bit of network traffic and perform an offline dictionary attack. For Slashdot readers, this probably seems trivial, but because Linksys, Apple, and others are letting users enter My Dog Has Fleas as their passphrase, WPA might be less secure for home users than WEP."
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New Wireless Security Standard Has Old Problem?

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  • Big deal (Score:5, Informative)

    by WolfWithoutAClause (162946) on Wednesday November 05, 2003 @08:59PM (#7402677) Homepage
    Just about any protocol allows dictionary attacks. Whilst some techniques, like salt, help, ultimately they make the problem for the bad guys only slightly harder.

    Only long passwords and encouraging the users to use good quality passwords/phrases really helps.

    Ultimately though, these passphrases are flawed anyway- they are a form of shared password. History has shown this to be a thoroughly bad idea, one passphrase per user/machine is a far better idea; and even the user shouldn't know what it is (that way it can't get beaten out of them- black cosh crytography works pretty darn well.) These standards organisations aren't even trying.

  • Mirror (Score:1, Informative)

    by Anonymous Coward on Wednesday November 05, 2003 @09:09PM (#7402748)
    Thought i would put up a mirror [ackbar.org] as it looks like the site is really slowing down and might die soon.
  • by TechyImmigrant (175943) * on Wednesday November 05, 2003 @09:15PM (#7402799) Journal
    The idea here (I know, I was there when we voted it into the standard) is that the PBKDF2 is computationally significant.

    Thus when you perform your offline dictionary attack, for each lookup in the dictionary, you must perform 4096 HMAC_SHA1s and this might take some time if you are looking up a large number of dictionary entries.

    The basic conflict is the wide disparity between the power of processors in low end 802.11 transceivers and high end computers. The time to compute the 4096 HMAC-SHA1s is significant on say a slow ARM7TDMI and the 4096 value is a compromise to limit the delay in computing this. This delay affects the time from pressing return on the keyboard, to the time the PTK can be known and communications can begin.

    However the attacker can apply his cluster of 3GHz PCs, or his FPGA HMAC_SHA1 parallel processor, or his supercomputer array, and make the speed of dictionary lookups relatively insignificant compared against the strength of the passwords being used.

    The wise people asked for a much higher number than 4096. Some implementation types beat it down to 4096, and here we are..

  • by hobbesmaster (592205) on Wednesday November 05, 2003 @09:19PM (#7402821)
    It takes far longer than that. Getting thousands of interesting packets takes weeks for a 256bit WEP network being used by only one person.

    And yes, this is from experience. I will neither confirm nor deny that I was given permission to try this...
  • by Dusty (10872) on Wednesday November 05, 2003 @09:19PM (#7402822) Homepage

    Ars Technica has a good summary of what you can do with SSID's and WEP to improve your wireless network's security:-

    Security Practicum: Essential Home Wireless Security Practices [arstechnica.com]
  • by timeOday (582209) on Wednesday November 05, 2003 @09:24PM (#7402866)
    The threat is way overblown. I'm willing to bet that fewer than 1% of WEP-protected access points fall to cryptographic weakness (but my guesstimate will yield immediately to anybody with ACTUAL DATA that agrees or disagrees). Any sensitive data you send, you should be (and probably are) sending over ssl (when the little lock appears in your browser window), using ssh instead of telnet, etc. As for Starbucks access points, they're not protected by WEP anyways.

    Just enable the WEP, use secure applications for sensitive data, and quit worrying about it.

  • by ch-chuck (9622) on Wednesday November 05, 2003 @09:25PM (#7402879) Homepage
    Don't worry, set him up, turn on wep, make some keys, and also use MAC filtering so only known stations can get in. To get around both those someone has to be fairly determined, just like someone determined to get in your house can probably do so, no matter what locks and alarms you install. That'll keep out the accidental neighbors and casual drive by scanners. Anything important like credit card numbers should be encrypted from browser to server with SSL anyway.

    Now, if a bank or hospital was going to install a wireless wep on a campus with account passwords etc in the air in the parking lot, then you'd have good reason to worry.

  • Re:My Dog Has Fleas (Score:5, Informative)

    by shird (566377) on Wednesday November 05, 2003 @09:27PM (#7402892) Homepage Journal
    Actually, a dictionary attack is inlikely to break 'My Dog has Fleas' because it is composed of multiple words, is fairly long, and has mixed case. Dictionary attacks typically involve just one or possibly two words strung together. Anymore and it becomes pretty impratical.

    The only pratical way to find that password is through brute force. In this scenario, the longer the password and more possible different characters (ie lowercase and uppercase, and spaces) makes it more difficult. Thus, 'My Dog has Fleas' would be more secure than 'mdhfaymdt' against a brute force attack. The latter could be broken in a matter of hours through brute force.
  • by nehril (115874) on Wednesday November 05, 2003 @09:34PM (#7402944)
    a good point, but that doesn't help against the offline dictionary attack listed in this paper: sniff some data, crack the password offline, THEN connect/spoof/raise hell. it will appear succeed on the first *visible to you* attempt.
  • by Anonymous Coward on Wednesday November 05, 2003 @09:47PM (#7403021)
    Where are you getting this stuff?!?

    assuming there are about 10K words in common vocabulary, and you use 10 words, that's about 10,000^10. pretty large, but only about 23 bits.

    10,000^10 ~ (2^13.3)^10 = 2^133 = 133 bits of encryption.

    but your 20 character password has a huge entropy. you have 26 lowercase letters, 26 uppercase letters, 10 numbers and about 10 punctuation marks. that's 66 possibilities per character. now 72^20 is a lot. that's about 26 bits.

    66 possibilities * 20 chars ~ (2^6)^20 = 2^120 = 120 bits of encryption.
  • Re:At least use WEP! (Score:5, Informative)

    by WuphonsReach (684551) on Wednesday November 05, 2003 @09:48PM (#7403028)
    We don't use WEP on our wireless net at the office. Too often, the interaction between the card and the access-point doesn't work well if WEP is enabled (different vendors for the two products).

    Instead, we've segregated all of the WAPs onto a dead-end network where the users have to VPN into our LAN through a border server. (Basically treating them as if they were outside the office and coming in from an external ISP.)

    Works pretty well, other then having to remember to VPN into the network. The traffic ends up encrypted (inside of the VPN tunnel), so it's not possible to sniff passwords.
  • by adrianbaugh (696007) on Wednesday November 05, 2003 @11:32PM (#7403680) Homepage Journal
    A program implementing a true brute force attack would be really stupid, though, at least for [J. Random Muppet]'s account; lots of time would be wasted trying aaaa, aaab, aaac etc., when the password is far more likely to be "password" or "150367". Once you force people to use passcodes of a length sufficient that even dumb people are likely to enter more than one word, or a word with at least one number, you enforce a level of security unbreakable by most entities over the average duration of a user's session. OK, that isn't anywhere near perfect but it's a lot better than allowing "password", "banana" or "slashdot"....
  • by Brad Mace (624801) on Thursday November 06, 2003 @12:36AM (#7404006) Homepage
    I think 1-2 days is more likely, especially with only one person using it. The important thing is that it's no longer about casually driving by and noticing it's open. Someone would have to invest a lot of time to get past it. It's doubtful anyone is going to bother. Even more so when they could just drive down the block and find an open node. using MAC filtering also makes more work for intruders, though they can sniff those from your traffic and spoof them.
  • by Brad Mace (624801) on Thursday November 06, 2003 @12:48AM (#7404072) Homepage
    If you're smart when you set up your access point, and turn on WEP, 99.9% of people that might hack your network are going to go find an easier target. The typical figure I've heard is 24 hours or more to get enough traffic to break the encryption. Unless someone knows you have something they want, they're not going to bother.

    Home users are going to generate less traffic than businesses, and so it will take even longer to get enough traffic. Unless you happen to notice a van parked outside your house for a couple days, or find yourself staring down the barrel of a pringles can, you can relax.

    1. Turn off SSID broadcasting
    2. use a unique SSID
    3. For God's sake, change the admin password
    4. Turn on WEP
    5. Use MAC address filtering
    Congratulations, you're now more trouble than you're worth.
  • Re:Kerberos (Score:2, Informative)

    by Bored Huge Krill (687363) on Thursday November 06, 2003 @01:42AM (#7404331)
    the problem isn't that passwords are sent over the network in the clear. They aren't. The problem is that any security system* that relies upon passwords as the basic secret is vulnerable to an offline dictionary attack; collect a sample of an exchange where the password was used somehow to encrypt a nonce also sent over the network, and try all the words in the dictionary that might be used as a password in an attempt to replicate the same exchange. When you get a match, bingo - you have the password.

    * there are some known systems that use passwords but which are not susceptible to this attack, invoving a carefully bound combination of passwords and a Diffie-Hellman exchange. I don't have a reference to hand, but such a system exists. Kerberos isn't it, though.

    Krill

  • by cookd (72933) <douglascook@@@juno...com> on Thursday November 06, 2003 @01:54AM (#7404414) Journal
    Kudos to a sibling post who brought up the fact that the only way to prevent this kind of attack is to limit the number of attempts possible in a span of time. The article/post failed to emphasize this enough.

    When possible, it is nice to find an algorithm or a protocol that allows two parties to authenticate without actually revealing enough information to identify the key.

    The lowest level of security would be where everything is out in the open for any observer -- they still have to observe, but one observation is all that is needed. For example, if you hand somebody your credit card, they have all of the information necessary to use it to steal from you -- it is all there on the card, perfectly legible. As another example, if you walk up to a terminal and type your password, anybody with camera pointed at the keyboard or some kind of electronic keylogger will be able to record your name and password on the wire, and then they know everything they need to know to take over your account.

    Things are slightly more secure when some additional work is required after getting the information. The old-school UNIX passwd file with encrypted passwords out in the open was like this -- anybody could copy the passwd file, but they would then have to run a cracker on it for a few weeks or months before anything useful showed up. Now that computers are faster and security is more of an issue, the passwd file is shadowed so that the passwd file doesn't actually have the encrypted passwords, which is a good thing because the original crypt algorithm can now be cracked pretty easily. Thus exploit is similar -- you can watch a session initiation, and with only that info, you can crack the password.
  • by cookd (72933) <douglascook@@@juno...com> on Friday November 07, 2003 @03:46AM (#7415090) Journal
    I fell asleep before I could finish my post last night, and I hit "submit" as I was drifting away. So continuing where I left off...

    There is a third category of transaction security, where even after observing the entire transaction, an eavesdropper doesn't have enough information to impersonate you. Generally, this takes the form of challenge-response. The server asks "42365?" and you answer "92581!" which is the correct answer. But an observer still doesn't know how to impersonate you, because next time, the server will ask "98765?" and the observer doesn't know that the answer is "45678!". Smart cards are like this, which is why they are more secure than credit cards or passwords.

    Each of these three categories still have varying degrees of security.

    In the first case, it is easy to use the information from a stolen credit card, but it would be pretty hard to make use of the information from a retinal scan. In both cases, you have all the information, but it's quite a pain to get your eyes replaced (if you get hungry, there's a sandwich and some milk in the fridge...).

    In the second case, while reversing a crypt password isn't too tough anymore, it still takes a bit of work to reverse engineer a 1024-bit RSA key. In both cases, the information is out in the clear, but factoring a 1024-bit number is a lot more work than running the crypt algorithm a few billion times.

    In the third case, "Mary had a what?" --> "Little lamb!" is easier than a smart card transaction.

    While we would love to have a cryptographically strong variation on the third case for every possible authentication/encryption transaction, it just isn't practical. In the case of WEP/WAP/Whatever, there are a lot of limitations to work around. It has to work on cheap hardware, it has to be fast enough to handle the traffic, it has to work in the face of many dropped packets, it can't inconvenience the user too much, etc.

    While I can think of a few things that I might have done differently, it seems like the new protocol is decent, given the limitations they were facing. While I wouldn't want to trust top-secret information to it, it seems that it is good enough for the average Joe.

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