Take the 2-minute tour ×
Server Fault is a question and answer site for professional system and network administrators. It's 100% free, no registration required.

I was helping a person with his computer today, and he was convinced that his router's WPA key was 7 characters (with some brand of consumer router). He has been able to connect with this on a number of computers, but when stepping him through it with Ubuntu we found that Network Manager imposes a strict limit of 8 or more characters.

Before I fire off a bug report, I would like to know: is that 8 or more character limit a hard, technical limit (and the guy on the phone just crazy), or is it indeed possible to have a WPA key with 7 characters?

share|improve this question
1  
Should be migrated to SU. –  Holocryptic Jul 28 '10 at 17:20
    
I don't know if it is possible, but it is almost certainly a bad idea. A password that small would be easy to guess through brute force. You may want to try to strongly encourage him to use something much longer. –  Zoredache Jul 28 '10 at 17:34
add comment

1 Answer

up vote 2 down vote accepted

WPA Pre-shared key (PSK) mode, defined in IEEE 802.11i-2004, uses PBKDF2 as described in PKCS #5. While PBKDF2 has no minimum length, the IEEE standard states in H.4 Suggested pass-phrase-to-PSK mapping (which includes a discussion of security considerations):

A pass-phrase is a sequence of between 8 and 63 ASCII-encoded characters. The limit of 63 comes from the desire to distinguish between a pass-phrase and a PSK displayed as 64 hexadecimal characters.

UPDATE: A thought occurs -- note that this is based on ASCII characters. Perhaps your 7-character WPA PSK has trailing whitespace!

share|improve this answer
    
Thanks for your help! That's probably what I should have asked the guy to do. Next time I come across this, I will try that :) Looking at the IEEE's spec, they only mention the minimum 8 characters thing once. In H.4.2 reference implementation, it isn't enforced and it doesn't look like the output would be wrongly influenced. Hm… Still a little lost, but I'm definitely less lost. –  Dylan McCall Jul 30 '10 at 3:14
add comment

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.