Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > sci.crypt > #32970

Re: storing passwords

Show all headers | View raw

On 2015-10-13 20:28:21 +0000, David Eather said:

> (assuming the actual storage device is tamper proof and cannot be 
> hacked - ok that one flaw but lets over look that)

If you really make that assumption then you might as well store the 
passwords in plaintext. The fact that you do not wish to do so tells me 
that you are (correctly) concerned about the device being hacked. 
(Under certain definitions of "hacked".)


> I have a salt and a large secret password (hard-coded into the tamper 
> proof design) such that the length of the salt and password makes 
> inverting a hash function practically impossible. To that I append a 
> short counter and the combined salt & long password & counter is hashed 
> to give a user password.

As someone pointed out

K = "large secret password (hard-coded) ...
salt = per record random salt
counter = "a short counter"

As someone else pointed out,

 HMAC(K, salt||counter||password)

is the usual construction for this. "K" is sometimes called "pepper". 
And its operations are often placed on an HSM (which I've also heard of 
as both "Hardware" or "Host")


> (just re-reading that I don't need a salt I can just use a longer 
> secret password)

No. You still need the salt. Its job is so that if two people use the 
same password, you cannot identify the fact that they do by inspecting 
the hashes. I'm not sure what the counter is for, though.

> If I have 2**n  - 1 passwords is it still impossible to guess or derive 
> the missing password? (I think yes)

Is n the the size of K? I *think* you are ok as long as you do use a 
random and unique salt for each and use something like HMAC.

Cheers,

-j

Back to sci.crypt | Previous | Next — Previous in thread | Find similar | Unroll thread

Thread

storing passwords "David Eather" <eather@tpg.com.au> - 2015-10-14 06:28 +1000
  Re: storing passwords Jakob Bohm <jb-usenet@wisemo.com> - 2015-10-13 23:06 +0200
    Re: storing passwords "David Eather" <eather@tpg.com.au> - 2015-10-15 08:45 +1000
  Re: storing passwords Paul Rubin <no.email@nospam.invalid> - 2015-10-13 14:22 -0700
    Re: storing passwords Jakob Bohm <jb-usenet@wisemo.com> - 2015-10-13 23:42 +0200
      Re: storing passwords Paul Rubin <no.email@nospam.invalid> - 2015-10-13 14:48 -0700
        Re: storing passwords Jakob Bohm <jb-usenet@wisemo.com> - 2015-10-14 00:09 +0200
          Re: storing passwords <william@wilbur.25thandClement.com> - 2015-10-16 18:08 -0700
            Re: storing passwords Jakob Bohm <jb-usenet@wisemo.com> - 2015-10-19 15:51 +0200
  Re: storing passwords "David Eather" <eather@tpg.com.au> - 2015-10-15 08:45 +1000
  Re: storing passwords Jeffrey Goldberg <nobody@goldmark.org> - 2015-10-15 15:51 -0500

csiph-web