Re: shared secret vulnerability

["Clint Chaplin" <cchaplin@sj.symbol.com>]

My impression is that hashing doesn't add any more entropy than was already present in the input.  Yes, hashing adds time to the calculation, but the output itself isn't any more entropic than the input was.  Am I incorrect?

Clint (JOATMON) Chaplin
>>> Joshua Wright <jwright@hasborg.com> 08/04/04 13:54 PM >>>
Paul Funk wrote:
 > The idea is that you take an ordinary secret, hash it many times,
 > and get a resulting "amplified" shared secret that multiplies the
 > difficulty of attack by the number of times it has been hashed. The
 > draft suggests 0x100000 (~ one million) iterations, adding 2 ^ 20
 > bits of effective entropy to the secret.

While I believe this algorithm is effective at adding entropy to a 
password such as the RADIUS secret, it does not resolve the issue of a 
widespread shared secret distributed throughout an organization. Without 
a mechanism in place to regularly change the secret, the use of shared 
secrets in this fashion is reminiscent of WEP pre-shared keys. As most 
people are painfully aware, shared secret do not stay secretive.

That being said, I like Paul's idea for effectively adding entropy to 
the shared secret that will prolong a brute-force attack.  However, I do 
not believe that this is effective at resolving weak authentication 
between the RADIUS authentication server and NAS.

-Joshua Wright
jwright@sans.org or
jwright@hasborg.com

-- 
-Joshua Wright
jwright@hasborg.com
http://home.jwu.edu/jwright/

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