I'm wondering if you might want a max size, but just not 14 characters. Maybe 256 or 1024. Reason: you don't want to hash a 2 GB password 1000 times => DOS. Erlend Gautam <itsecanalyst@gmail.com> wrote: > 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@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@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@telmon.org >> > http://www.telmon.org >> > >> > >> > _______________________________________________ >> > The Web Security Mailing List >> > >> > WebSecurity RSS Feed >> > http://www.webappsec.org/rss/websecurity.rss >> > >> > Join WASC on LinkedIn http://www.linkedin.com/e/gis/83336/4B20E4374DBA >> > >> > WASC on Twitter >> > http://twitter.com/wascupdates >> > >> > websecurity@lists.webappsec.org >> > >> http://lists.webappsec.org/mailman/listinfo/websecurity_lists.webappsec.org >> > >_______________________________________________ >The Web Security Mailing List > >WebSecurity RSS Feed >http://www.webappsec.org/rss/websecurity.rss > >Join WASC on LinkedIn http://www.linkedin.com/e/gis/83336/4B20E4374DBA > >WASC on Twitter >http://twitter.com/wascupdates > >websecurity@lists.webappsec.org >http://lists.webappsec.org/mailman/listinfo/websecurity_lists.webappsec.org

Thanks Nilesh, that link helped, @Erlend, I am going to suggest 256 as max length, since i don't think anyone would even go close to it and then everything is going be salted-hashed anyways. One reason i would want to set some MAX length is the client team wants to check the input again some max value instead of accepting a large buffer (not fully convinced on this, but have to live with it). Let me know if it makes sense. Thanks, Gautam On Mon, May 23, 2011 at 6:56 AM, Erlend Oftedal <erlend@oftedal.no> wrote: > I'm wondering if you might want a max size, but just not 14 characters. > Maybe 256 or 1024. > Reason: you don't want to hash a 2 GB password 1000 times => DOS. > > Erlend > > Gautam <itsecanalyst@gmail.com> wrote: > > > 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@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@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@telmon.org > >> > http://www.telmon.org > >> > > >> > > >> > _______________________________________________ > >> > The Web Security Mailing List > >> > > >> > WebSecurity RSS Feed > >> > http://www.webappsec.org/rss/websecurity.rss > >> > > >> > Join WASC on LinkedIn > http://www.linkedin.com/e/gis/83336/4B20E4374DBA > >> > > >> > WASC on Twitter > >> > http://twitter.com/wascupdates > >> > > >> > websecurity@lists.webappsec.org > >> > > >> > http://lists.webappsec.org/mailman/listinfo/websecurity_lists.webappsec.org > >> > > > >_______________________________________________ > >The Web Security Mailing List > > > >WebSecurity RSS Feed > >http://www.webappsec.org/rss/websecurity.rss > > > >Join WASC on LinkedIn http://www.linkedin.com/e/gis/83336/4B20E4374DBA > > > >WASC on Twitter > >http://twitter.com/wascupdates > > > >websecurity@lists.webappsec.org > > > http://lists.webappsec.org/mailman/listinfo/websecurity_lists.webappsec.org > _______________________________________________ > The Web Security Mailing List > > WebSecurity RSS Feed > http://www.webappsec.org/rss/websecurity.rss > > Join WASC on LinkedIn http://www.linkedin.com/e/gis/83336/4B20E4374DBA > > WASC on Twitter > http://twitter.com/wascupdates > > websecurity@lists.webappsec.org > http://lists.webappsec.org/mailman/listinfo/websecurity_lists.webappsec.org > -- Regards, Gautam