Re: Password derived key with hash iterations

From: Jed Davis (jdev_at_panix.com)
Date: 07/29/03

  • Next message: Peter Smyth: "Re: Entropy-distributing functions?" 
    Date: Tue, 29 Jul 2003 12:11:14 -0400

    cppdev9@yahoo.com (cppdev) writes:

    > Hello,
    >
    > In some libraries I see a password deriving
    > function. It takes a hash iteration count.
    > Does iterating over original password's hash let's
    > say 100 times really gives any security?
    > It seems that all someone has to know to get the key
    > is the hash before the last one, am i missing something?

    The idea, I assume, is to make it harder to use a dictionary attack on
    the original password typed by the user. Guessing any of the
    intermediate stages should be as hard as guessing the eventual key,
    since with a good hash function they might as well be random bits.

    Of course, if this 100x-hash isn't salted (some random bytes added to
    the password before hashing and included with the ciphertext), the
    attacker can precompute the 100x-hashes of their dictionary file and
    apply them to any ciphertext. 

    -- 
Jed Davis               |"But life wasn't yes-no, on-off.  Life was shades of
<jdev@panix.com>        | gray, and rainbows not in the order of the spectrum."
<jldavis@cs.oberlin.edu>|   -- L. E. Modesitt, Jr., _Adiamante_
PGP key (fingerable) F33659F9 A098:903E:9B9A:DEF4:168F:AA09:BF07:807E:F336:59F9
  • Next message: Peter Smyth: "Re: Entropy-distributing functions?"

    Relevant Pages

    • Re: hv_iterinit has side effects - who cares about PL theory
      ... > Thanks for backing me up Xho. ... If I want to do a hash read from the beginning, ... I didn't know I was backing you up! ... It seems to me that you are insisting a hash iteration is ...
      (comp.lang.perl.misc)
    • Password derived key with hash iterations
      ... In some libraries I see a password deriving ... It takes a hash iteration count. ...
      (sci.crypt)
    • Re: hv_iterinit has side effects - who cares about PL theory
      ... Also sprach ctcgag@hotmail.com: ... If I want to do a hash read from the beginning, ... It seems to me that you are insisting a hash iteration is ... > evidenced by the fact that you need to call init in your pseudocode). ...
      (comp.lang.perl.misc)
    • Re: newbie: please help...just your opinion
      ... knowing both gives you the first key char. ... > only if the bits of rand# and pre-xor hash were different or equal... ... > presence of a new char in the ciphertext - one should try to add only ... So imagine an attack where the attacker guesses the length of the ...
      (sci.crypt)
    • Re: PasswordOption.SendNone
      ... the client sign or encrypt the HASH of the message with ... The Message together with the Ciphertext ... is then sent over to the WS together with the username. ... client) from a database or whatever storage medium you have...(This model ...
      (microsoft.public.dotnet.framework.webservices.enhancements)