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sorry im kinda clueless with this stuff... I heard if you set your wifi password to more than 10 or so digits (and make it complicated), then your wpa / wpa2 psk would be safe. Is that true? If not, how do i make it secure so that i dont have to revert to Wired (=safe?)? I just need it to be secure for one day at a time. (I mean I can keep resetting password if that helps)

Candy
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    Yes, WPA2 is generally considered secure as long as you have s strong password - the only known way to crack it is essentially by guessing/brute-force. If your router has WPS, also make sure it is disabled. – tlng05 Jul 23 '15 at 17:09

2 Answers2

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If a password is strong, then it is strong. WPA2 uses PBKDF2 with 4096 iterations and the network SSID as salt to turn the password into the shared secret. This is not bad. This means that a "strong" password will be, in this case, a password with 68 bits of entropy or more: the 4096 iterations add 12 bits to the brute force effort, and I use the traditional "80 bits" as the threshold of attacker's power. Note that 280 is a lot, and an attacker who is interested in obtaining a free Internet access through your WiFi is unlikely to devote that much computing power to the effort. A weaker password in the 40-bit entropy range will already be strong enough to deter attackers.

This famous question discusses password generation and entropy. A password with 40 bits of entropy can still be compatible with a human brain.

Password derivation aside, there is no known weakness in WPA2, so you can say that with a strong password, WPA2/PSK is safe... within its functionality. Remember the following points:

  • WPA2 is about keeping outsiders outside. It prevents external attackers from joining the network, i.e. looking at existing traffic and inserting his own. However, WPA2 does not protect connected clients from each other.

  • Even without piercing the crypto layer, attackers will still be able to do some traffic analysis: they can track the client machines (their MAC addresses are visible) and get some idea of what they say based on the timing and size of each frame.

  • Attackers who just want to achieve wanton disruption can jam the traffic by simply emitting stronger radio waves at the same frequency; and they can do that remotely. To do the same with a wired network requires physical access to the wires. For instance, your neighbour can jam your WiFi without leaving his house, while breaking your wire network would require entering your home.

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Thomas Pornin
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  • I don't think 40 bits of entropy is really enough to deter an attacker if you're using a common SSID like linksys or netgear, as many people are. In that case there's existing rainbow tables that require little or no computation to be effective. Quick googling reveals there's some trivial ones available for download. http://www.renderlab.net/projects/WPA-tables/ – Steve Sether Jul 23 '15 at 18:40
  • 40 bits coupled with the 4096 iterations means 2^52 invocations of HMAC (2^53 invocations of SHA-1), which is a huge effort. In fact, the tables you link to indicate that they were generated to cover 1 million passwords, for 1000 "most common" SSID. This means that a 40-bit entropy password has probability at most 1/1000000 of being crackable with these tables (probably less than that in practice), and that is assuming that your SSID is indeed part of the 1000 most common SSID. – Thomas Pornin Jul 23 '15 at 19:13
  • Of course, larger cracking efforts may exist, but I doubt they would get even close of a 40-bit password space for 1000 SSID. Even for a single SSID, this is still an effort 1000 times heavier than what the authors of these tables actually did. – Thomas Pornin Jul 23 '15 at 19:16
  • According to this site: https://hashcat.net/oclhashcat/ SHA1 can be done one a single, powerful PC at 31,552 million hashes/second. 2^53= 9 x 10^15. 9*10^15/31,552,000,000= 3.3 days. So you can generate the entire rainbow table for a single SSID in just over 3 days for a 40 bit password. I think that's extremely feasible. – Steve Sether Jul 23 '15 at 20:01
  • Oh, and if you use the WPA/WPA2 rate quoted on the same sight, the numbers are 8.8 days. – Steve Sether Jul 23 '15 at 20:11
  • That's for a _powerful_ PC: it includes _eight_ heavy GPU (notably, this means about 2400W to feed the GPU, and some more to prevent them from melting). So yes, some things are _doable_, but expensive -- that's for a single SSID after all. (Also, factor in a 1.7x factor because rainbow tables need some overlap.) – Thomas Pornin Jul 23 '15 at 20:14
  • I wouldn't call that an expensive PC. I could personally buy it and calculate the rainbow tables for 40 bits of entropy for the top 40 SSIDs in less than a year and publish them. That's just not a lot of effort, and I'm not a rich person. – Steve Sether Jul 23 '15 at 20:21
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Choose a cryptographically strong PRNG to generate a 12 characters password. That will too sufficient because it will give you 71 bits of entropy, which is safe and secure against all of the attacks that attackers might try to attack your password. This way, you do not need to change your password everyday and it is not only too secure but also practical in case you type it on a smartphone.