[WEB SECURITY] Max size of a password

Gautam itsecanalyst at gmail.com
Sun May 22 14:46:35 EDT 2011


 Claudio, Albino and James, You gave me the exact answer I was looking for,
i know about hashing and other things, however the entropy stuff probably
was known to me in full. I read a couple of papers from NIST last night to
understand this better.

I am also going to add the 2nd factor auth in my recommendation, since most
of the stuff is what you know, what you have is where I want to take this
and probably What you are will be next.

Thanks to all.

Gautam

On Sun, May 22, 2011 at 11:24 AM, James Manico <jim at manico.net> wrote:

> Then again, hashing and salting is not enough for secure password storage.
>
> 1) Use a strong/modern hash
> 2) Use a cryptographically strong salt
> 2a) Isolate that salt from the actual hash
> 3) Iterate the hashing of the pass and salt 1000 times (as of y2k,
> doubling that iteration value every three years when you re-hash to
> slow down re-construction of the custom hash table if the salt is know
> by the attacker)
> 4) For %#^* sakes, stop depending on password as the only factor for
> authentication. Shifting to 2-factor strategies decreases the need for
> strong password policy or storage mechanisms.
>
> Jim Manico
>
> On May 22, 2011, at 7:46 PM, Claudio Telmon <claudio at telmon.org> wrote:
>
> > On 05/22/2011 12:33 AM, Gautam wrote:
> >> Now my delima is
> >>
> >> SHA256(*AAA*)  = some 256 bit hash
> >>
> >> now
> >>
> >> SHA256(*AAABB*) = is also 256 bit hash
> >>
> >> so with this reasoning will it make sense if i say no limit or just a
> >> reasonable limit of 14 character since the result is always going to be
> >> 128bit text be it 8 characters or 14 characters.
> >
> > A good hash function can provide you an entropy which is limited by the
> > length of the output, but the entropy available in the input domain is
> > also a limit. 14 characters as input from a user are not random bits and
> > won't provide 128 bit of entropy for the result. If users are permitted
> > (and suggested) to choose long passphrases, they may end up feeding the
> > function with enough entropy. If they are limited to 14 characters, they
> > will select passwords that will be shorter that 14 characters and are
> > not random, so they will always feed less that 128 bit of entropy to the
> > function, and the output will also have less that 128 bits of entropy,
> > even if it is 128 bit long.
> >
> > ciao
> >
> > - Claudio
> >
> > --
> >
> > Claudio Telmon
> > claudio at telmon.org
> > http://www.telmon.org
> >
> >
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