I've read some articles saying you should set the cost to be at least 16 (216), yet others say 8 or so is fine.
Is there any official standard for how high the cost should be set to?
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- 2Set it so that your users just don't rebel because login takes too long.Paŭlo Ebermann– Paŭlo Ebermann2011-10-01 23:29:15 +00:00Commented Oct 1, 2011 at 23:29
- here was already got explained ancwers security.stackexchange.com/questions/17207/… cheers !Vladimir Ch– Vladimir Ch2016-11-02 04:45:12 +00:00Commented Nov 2, 2016 at 4:45
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3 Answers
The cost you should use depends on how fast your hardware (and implementation) is.
Generally speaking a cost of 8 or 10 is fine -- there isn't any noticable delay. It's still a huge level of protection and far better than any home-grown solution using SHAs and salts. Once you upgrade your hardware you could increase the cost to 16. I would say that 16 is a little high at this time, and will probably result in noticeable (and annoying) delays. But if 16 works for you, by all means go for it!
5 Comments
Obto
Thanks for the confirmation/clarification that a cost of 8 is safe. Never want to take any chances with stuff like this haha
erickson
8 or 10 is nowhere close to enough. 12 or 13 maybe.
Joost Baaij
erickson - can you substantiate your claim? (and your downvote)
Joost Baaij
If you think 7 seconds is too long, then you should stay at 10.
You must set the number of iterations at the maximum value which is still "tolerable" depending on the hardware you use and the patience of the users. Higher is better.
The whole point of the iteration count is to make the password processing slow -- that is, to make it slow for the attacker who "tries" potential passwords. The slower the better. Unfortunately, raising the iteration count makes it slow for you too...
As a rule of thumb, consider that an attacker will break passwords by trying, on average, about 10 millions (107) of potential passwords. If you set the iteration count so that password hashing takes 1 second for you, and you consider that the attacker can muster ten times more computing power than you, then it will take him 107*1/10 seconds, i.e. about 12 days. If you set the iteration count so that password hashing takes only 0.01 second on your PC, then the attacker is done in three hours.
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The cost should depend on your hardware.
You should test your cost settings and aim for the 100 .. 500 ms interval. Of course, if you are working with highly sensitive information, the time could be 1000 ms or even more.
