[Owasp-leaders] Password Storage and Hash Chaining

Eoin eoin.keary at owasp.org
Sun Jul 1 21:35:37 UTC 2012


Cool, but be mindful of the root cause of the breach? Should we not also focus on the protection mechanisms surrounding the data in the first place.
(I love throwing monkey spanners about)
Eoin.

 

Eoin Keary
Owasp Global Board
+353 87 977 2988


On 1 Jul 2012, at 21:53, Jim Manico <jim.manico at owasp.org> wrote:

> A lot of people are looking at the password storage cheat sheet due to
> recent breaches.
> 
> One of the recommendations we make is regarding "hash chaining" which is
> to repeat the hash algorithm many times to slow down cracking of hashed
> passwords.
> 
> Bcrypt does this (and in general is a good choice for password storage),
> but is often not permitted in some organizations due to it's blowfish
> roots.
> 
> So when we cannot use B/S-Crypt, we recommend (ie: via ESAPI and the
> Password Storage Cheat-sheet) the use of one of the SHA family of
> algorithms. In addition to hashing we of course recommend salting. SHA
> variants are insanely fast, and to slow down password cracking we
> recommend hash iteration (which is really formally called "Hash Chaining").
> 
> One of the big mistakes we have made in ESAPI and in the Password
> Storage cheat-sheet is that we recommend iterating the just the hash.
> There is no cryptographic benefit to this mechanism in the face of large
> rainbow tables, which do indeed exist.
> 
> So this pseudo code from ESAPI is a (total) failure in terms of slowing
> down SHA-based password storage:
> 
> // rehash a number of times to help strengthen weak passwords
> bytes = hash(user-salt + system-salt + password)
> for (inti= 0; i< iterations; i++) {
>    bytes = hash(bytes)
> }
> 
> And the more cryptographically sound way to store a password based on
> SHA is something along the lines of:
> 
> // rehash a number of times to help strengthen weak passwords
> bytes = hash(user-salt + system-salt + password)
> for (inti= 0; i< iterations; i++) {
>    bytes = hash(bytes + user-salt + system-salt + password + hash(i))
> }
> 
> I advise that the ESAPI team consider strengthening the current Java
> implementation. The cheat-sheet team will make changes to the Password
> Storage Cheatsheet as well in the near future. For more information,
> please read up on the Merkle theorem (Merkle's time-memory trade-off to
> be more specific).
> 
> I am admittedly not a cryptographer, or even an applied cryptographer.
> :) Comments are greatly appreciated. I think we have a long way to go as
> a community to clarify the best way to store a password.  John Steven -
> looking forward to the next iteration of your threat model. :)
> 
> --
> Jim Manico
> 
> Connections Committee Chair
> Cheatsheet Series Product Manager
> OWASP Podcast Producer/Host
> 
> jim at owasp.org
> www.owasp.org
> _______________________________________________
> OWASP-Leaders mailing list
> OWASP-Leaders at lists.owasp.org
> https://lists.owasp.org/mailman/listinfo/owasp-leaders


More information about the OWASP-Leaders mailing list