What is a Pre-Shared key

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Level 2

185 points

What is a Pre-Shared key

When setting up the airport extreme base station with WPA2 Personal security I am given the option of entering a password between 8 to 63 characters, or a 64 character hexadecimal Pre-Shared key.

Should I be interested in using a pre-shared key? Does it require anything different from simply entering a very long password? Does it do anything differently once it's set up?

At first sight it looks like 63 randomly chosen ascii characters will be more secure, harder to guess, than 64 hexadecimal. And I am confused.

G5 single processor 1.6MHz, Mac OS X (10.4.7), PowerBook 15"

Posted on Sep 21, 2006 10:25 PM

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Answer 1

Sep 22, 2006 6:10 AM in response to MacPeter

Unless you're running a radius server, you'll need a pre-shared key to run WPA. This is a key that is the start of the WPA encryption process. It's something that both the access point and client know.

Your WPA PSK should be as long as possible. I like to use the first stanza of a poem or the words to a song, either run together or just the first letters of each word depending upon length. Like, "WwtaItIkhhiitvt" for "Whose woods these are I think I know his house is in the village though". And no, that's not my PSK (I prefer the works of Steinbeck).

However, you'll probably want to balance the length against the practical use of the password and your security needs. The longer the better, but remember you'll need to provide your PSK to each wireless client.

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Answer 2

MacPeter Author

Level 2

185 points

Sep 23, 2006 12:54 PM in response to Jeff Breitner

thanks, this doesn't really answer my question: the thing is that the apple front end asks for either a password (which I suppose by its very nature is preshared) of between 8 and 63 characters long or a preshared key in hexadecimal which has to be exactly 64 hexadecimal characters. So the preshared key has a fixed length : always exactly 64 chars. Whereas obviously a password could be of various lengths. So I still do not understand....

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Answer 3

Sep 23, 2006 1:31 PM in response to MacPeter

The plaintext password is run against a fixed hash that generates the 256-bit PSK (64 characters). The output is your 64 hexadecimal characters.

If your plaintext password isn't long enough, it fills the voids for you.

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Answer 4

MacPeter Author

Level 2

185 points

Sep 24, 2006 4:12 AM in response to Jeff Breitner

Thanks, that seems to be the answer!!!

It still seems curious that there will be a great many more 63 ascii character strings than 64 hexadecimal hashes: it must just simply be that many different passwords will theoretically give rise to the same hash.

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