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I have a wireless router, and I want a difficult password that is still, in a way, easy to remember.

I came up with this idea to take the MD5, SHA-1, SHA-256, or whatever hash of a common English word, such as "superuser" and use the hash as the WPA2 key.

For example, let's say that "superuser" was my word of choice. If I chose SHA-1 has my hash, I would then set up my WPA2 key to be8e67bb26b358e2ed20fe552ed6fb832f397a507d.

Is this a secure practice? Common English words are being used--in a way--in the key, but the key itself is actually a long, complex hexadecimal string.

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Not secure now that you mentioned it :) –  RCIX Nov 28 '09 at 11:09

3 Answers 3

up vote 3 down vote accepted

Unless you reveal the method of how you generated you "long WPA2" key (which you just did), it is just a random string of text which would normally be pretty secure. On the other hand, if someone knew that you were using "a common English word" and used a hash of that word as the key, anyone could quickly generate a sequence of hashes from a dictionary and break your password pretty quickly.

If you are looking for a "difficult password that is still easy to remember" why don't you come up with a longer pass phrase that means something to you but not easily guessed by anybody else. Start with a phrase (i.e. sequence of words, sentence, etc), mix in a sequence of digits that mean something to you (apart from birthdays, phone numbers, etc), and generate a long key that is "easy to remember" that way.

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I'm with Wil & Robert on this one. A passphrase is generally more secure than a password - just the length makes guessing your phrase that much more difficult. –  DaveParillo Nov 28 '09 at 1:14
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I mostly agree, except for that a hash of an english word is not a random string of text. It is what it is, a hash of an English word. In other words: The proposed method doesn't enlarge key space, but it does render widespread rainbow tables useless. Given the fact that generating a rainbow table is not that easy, this is a good thing. To enlarge key space you might consider encrypting your password with a salt. –  Ludwig Weinzierl Nov 28 '09 at 9:27

It is as secure as any other key as long as you do not tell anyone.

At the end of the day, your key will be using 0-9, a-f... which is actually only gives 16 possible characters instead of just a-z which would give 26. Therefore, if you think you are being smart and tell someone "I am using SHA-1", you are actually cutting down their brute force combinations by quite a few.

Personally, I think you would be a lot better off just having a normal long word/s with a mix of case, then throw in some random numbers and symbols.

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True, but I would say that 'throwing in some random numbers & symbols' don't contribute greatly to making it easier to remember. How about throwing in some non-random numbers ;-) –  DaveParillo Nov 28 '09 at 1:16
    
True - but then again, since when is a SHA-1 key easy to remember? –  William Hilsum Nov 28 '09 at 1:26
    
interesting point... maybe a) salt the word, b) hash with sha-256, and c) convert the result from hex (base-16) to base-26 (a..z) or even base-36 (0..9,a..z). –  quack quixote Nov 28 '09 at 3:00
    
Personally, I think it is just best to use a long unique password such as "this_is!my.password,for2the3week_of30/11/09"... And change it every week to be slightly different... Will give you a fraction of the problems and harder to crack! –  William Hilsum Nov 28 '09 at 3:48
    
that's not a bad method either... between the two it's somewhat a matter of individual taste. your example would certainly be easier to remember. –  quack quixote Nov 28 '09 at 9:30

It is safe as long as nobody can possibly figure out the method. This of course includes bragging about it in the office, but also traces of any kind you may leave behind. As an example, if you are to connect a random user to your network, you'll probably use some kind of client-side application to generate the hash. If the random user then notices that there's an echo "superuser" | sha1sum in the log it's not too hard to add the two together.

Seeing as you'd have to generate the hash externally, much of the convenience disappears. Generally I'd say that hashing a common word might be an acceptable way to quickly generate a semi-random key, but the key must still be copied or remembered when entering to not pose a weakness.

The only other gain I can think of is that the key/phrase/password can be easily reproduced if lost. If above security-measures are taken I see no reason not to use hashed words as keys.

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