Salt
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From: Kristian Gj�steen on 24 Feb 2010 13:17 Buzz <b(a)b.com> wrote: > >"Paulo Marques" <pmarques(a)grupopie.com> wrote in message >news:ppadnW2MKODc3BjWnZ2dnUVZ8nWdnZ2d(a)novis.pt... >> Buzz wrote: >>> "Kristian Gj�steen" <kristiag+news(a)math.ntnu.no> wrote in message >>> [...] >>>> Add a sufficiently big salt and it will be impossible to build such >>>> a table. To invert the hashing, you now need to search the entire >>>> small space. >>> >>> So if I understand correctly, the basic purpose of a salt is this. >>> - It would be very inconvinient for a user if you enforce that a password >>> has to be very large - say 20 chars long. >>> - So instead you enforce a 8 char long limit & generate & add a 12 char >>> long salt(per user). You store the user's salted hashed password & the >>> hash >>> at one place. >> >> Don't think in terms of limiting the password size (which is bad), but >> just user convenience. > >I was referring to minimum limit, not maximum. I don't think that is bad. >If your minimum limit is 8, then using a 8 char password + 4 char salt would >offer the same security as if your minimum limit was 12, but more >convinient. No. The salt is available to the attacker. >What is key stretching? Google? Increase the time for key derivation by some factor, and you increase the cost of the password search by the same factor. -- Kristian Gj�steen
From: Maaartin on 24 Feb 2010 13:59 On Feb 24, 4:34 pm, "Buzz" <b...(a)b.com> wrote: > "Paulo Marques" <pmarq...(a)grupopie.com> wrote in message > > I was referring to minimum limit, not maximum. I don't think that is bad. > If your minimum limit is 8, then using a 8 char password + 4 char salt would > offer the same security as if your minimum limit was 12, but more > convinient. No. Against somebody trying to crack a single password, the security of 8 char password + 4 char salt is exactly the same as the security of 8 char password alone (ignoring the fact that he can use a preexisting 8 char rainbow table). You only get more security against somebody trying to crack multiple passwords at the same time - he has to deal with 12 characters instead of 8 (assuming the salt is different for different passwords). I know it was already written but you seem to ignore it.
From: Buzz on 24 Feb 2010 20:54 Consider a case where I have one resource exactly which is protected by a user password. I store the salted hash & the salt at the same place & it's public. In such a case, using a salted hash instead of a simple hash has given no extra security & one need not go through the extra effort & just use a simple hash. Is this true? "Maaartin" <grajcar1(a)seznam.cz> wrote in message news:19a5a775-c915-486a-ac4d-342c47afde82(a)g19g2000yqe.googlegroups.com... On Feb 24, 4:34 pm, "Buzz" <b...(a)b.com> wrote: > "Paulo Marques" <pmarq...(a)grupopie.com> wrote in message > > I was referring to minimum limit, not maximum. I don't think that is bad. > If your minimum limit is 8, then using a 8 char password + 4 char salt > would > offer the same security as if your minimum limit was 12, but more > convinient. No. Against somebody trying to crack a single password, the security of 8 char password + 4 char salt is exactly the same as the security of 8 char password alone (ignoring the fact that he can use a preexisting 8 char rainbow table). You only get more security against somebody trying to crack multiple passwords at the same time - he has to deal with 12 characters instead of 8 (assuming the salt is different for different passwords). I know it was already written but you seem to ignore it.
From: Gordon Burditt on 25 Feb 2010 01:26
>Consider a case where I have one resource exactly which is protected >by a user password. Ok, you have the one and only credit card in the universe. Oh, yes, and you never change the password to one you've used before. >I store the salted hash & the salt at the same place & it's public. >In such a case, using a salted hash instead of a simple hash has >given no extra security & one need not go through the extra effort >& just use a simple hash. >Is this true? Yes. But you are not the only one in the universe who has a credit card. Using a salt will help avoid the attacker being able to re-use any tables built to attack other people's credit cards to attack yours. Another issue is that with lots of credit cards it's possible (without the hash) to quickly find all the credit cards with the *same* password (since the hash will be the same). That might be used to find several credit cards likely owned by the same person. |