Wireless security in a nutshell:
WEP and WPA(1) both use the RC4 stream cipher for the underlying encryption. RC4 is no longer considered "strong", but only in the sense that distributed computing and/or massive super computers might eventually crack it. That said, there is a known-plaintext attack against RC4 (and therefore against both WEP and WPA) that would theoretically allow reading data from very short packets containing mostly known text. Moreover, due to a weakness in WPA's integrity algo (WEP's is even worse), it is theoretically possible to
inject data undetected into said very small packets. There's no direct vulnerability here, but it could allow some indirect attacks against the network, at least if it connects to the internet. Either way, this is a very sophisticated attack that would be beyond the reach of even amateur crackers (let alone script kiddies) even supposing that you had the right tools (which as I understand it are not yet complete).
Where WEP horribly fails compared to WPA is that it uses a highly flawed method to derive the RC4 traffic keys from the WEP key. In short, it allows an attacker to fully reverse the WEP key just by sniffing traffic over a relatively short amount of time (usually just a few minutes). WPA replaces that flawed method with TKIP, for which there are not any known attacks.
WEP's authentication schemes -- Open System and Pre Shared Key -- are both also quite flawed. PSK moreso than open system. This is mostly moot, though, since both auth methods merely require knowledge of the WEP key, which can be trivially cracked, per above. In contrast, WPA uses the same auth methods as WPA2: WPA-Personal and WPA-Enterprise. More on that later.
WPA2 uses CCMP, which is entirely different from both WPA and WEP. CCMP is based on AES-128 encryption, and is very strong. The message integrity method is also improved over TKIP, preventing the sort of injection attack theoretically possible with WPA. There are some theoretical crypto attacks against AES in general, but nothing that would allow actual cracking except maybe by three-letter agencies (who knows?)
For authentication, WPA and WPA2 both allow for either WPA-Personal, or WPA-Enterprise.
WPA-Personal uses a single 256-bit key shared with all devices to authenticate them. The key can be entered directly in hex, or generated by a hashing algo from a password. The strength of this system depends on the strength of the password and the trustworthiness of the users. Weak passwords can be bruteforced -- very quickly if you use a common SSID name, which enables the use of rainbow tables. Dishonest or incompetent users can of course leak the key.
WPA-Enterprise is basically just EAP authentication with a RADIUS server. Since RADIUS is open-ended, you could be authenticating against just about anything using just about any kind of credentials. It could use something as simple as user/pass auth or something as complicated as two-factor auth using a smart card/RSA frob/biometrics.
So depending on how you personally implement them, both WPA-Personal and WPA-Enterprise can be anywhere from extremely weak to extremely strong.
In the end analysis:
- If WPA2 is available, use that. If your router supports "mixed mode" (a.k.a. CCMP +TKIP, AES + TKIP, WPA + WPA2), only clients which actually use WPA/TKIP will be vulnerable to the theoretical injection attack, so it's not really dangerous to leave on. However, if you aren't using it, go ahead and disable it.
- If only WPA is available, don't freak. Practically speaking, you're still secure against all but sophisticated crackers, and even then there are a lot of mitigating factors about what harm could actually be acomplished. Either way, no sensitive traffic can be decrypted, nor can your network be used by an unauthorized attacker. Upgrade to WPA2 when you can, but don't feel like you have to rush out and do it now.
- If only WEP is available, buy a new router. Do it right now. WEP is completely, 100% insecure no matter what you do.
- MAC filtering is largely pointless. WPA/WPA2 are all vastly greater barriers to unauthorized access than MAC filtering. And as for WEP, it's a given that anyone who can crack WEP can also get around MAC filtering.
- SSID hiding is also mostly pointless. It's trivial to reveal hidden SSIDs with common tools and no knowledge. Moreover, when you take a device out of range of your hidden SSID, it will constantly try to reconnect to it. That is, it can't tell if an AP with that SSID is in range or not precisely because the AP doesn't broadcast its SSID. This matters because every time it does so, it broadcasts the name of your SSID to everyone within earshot. In a sense, this is worse than having your AP broadcast a SSID, since your AP at least stays in once place and can thus only be heard by people near your house. Your laptop or cellphone goes all over the place. Admittedly, this is a minor point and would only matter with a determined hacker, but the tools for doing this exist and don't require any particularly special knowledge to use.
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