[clug] MD5 of an MD5 checksum

Jepri jepri at webone.com.au
Fri Mar 12 13:15:26 GMT 2004

Hi Leigh!

Leigh Makewell wrote:

>   Or more specifically they generate a random 3 character salt and 
> then do an md5(md5(password)+salt)
> As far as I can tell this is in no way more secure than just doing an 
> md5 of the password, and I have a nagging feeling that it's actually 
> less secure (although maybe the random salt overcomes that problem)

It is slightly more secure, in the same way that choosing your password 
to be 'Leigh1234' is slightly more secure than choosing 'Leigh' as your 

You are probably remembering a monograph by Bruce Schneir on why not to 
trust amateur crypto implementations because doing things like repeating 
a cipher can weaken it.   I can't find a link right now.  How annoying, 
I've read it about ten times...

In this case you should be OK, because MD5 is a hash (a one way 
function), and not a cipher (a reversable algorithm).

> Can anyone think of any reason to do it this way? (Apart from 
> completely making their system incompatible with anything else)

MD5 should be secure enough on its own.  I base this suggestion on the 
observation that a number of knowledgable and paranoid people use it.


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