Hacker News Reader

Comment by rudolf0 | Hacker News Reader

The default cost for most libraries and languages is between 10 and 12, which is considered too low for 2015 but still pretty good. As long as they're at the default or above it, I wouldn't be too concerned about an attack against the whole DB.

Targeted cracking attempts against specific hashes are definitely still an issue though.

View on HN

If I set bcrypt cost to 11, hashing takes 0.1 seconds. At 12, it takes 1 second roughly. Setting it to anything higher leaves my service open to Denial-of-Service attacks, so I'm very hesitant to increase the cost factor.
To you have a credible source for the "10..12 is too low for 2015" claim?

HHVM 3.6 on a small Ubuntu server

You have either a very slow server or a very bad bcrypt implementation. Running bcrypt in python on my 5 year old server has these results:

>>> timeit.timeit("bcrypt.hashpw('this is a password', bcrypt.gensalt(11))", setup="import bcrypt", number=5) / 5

0.13497538566589357

>>> timeit.timeit("bcrypt.hashpw('this is a password', bcrypt.gensalt(12))", setup="import bcrypt", number=5) / 5

0.28287739753723146

>>> timeit.timeit("bcrypt.hashpw('this is a password', bcrypt.gensalt(13))", setup="import bcrypt", number=5) / 5

0.5341608047485351

>>> timeit.timeit("bcrypt.hashpw('this is a password', bcrypt.gensalt(14))", setup="import bcrypt", number=5) / 5

1.069920015335083

>>> timeit.timeit("bcrypt.hashpw('this is a password', bcrypt.gensalt(15))", setup="import bcrypt", number=5) / 5

2.151028203964233

That's five repetitions of a bcrypt hash with the work factor passed in bcrypt.gensalt(). The resulting units are seconds.

You are right, my times are apparently somewhat dated. HHVM 3.6 actually gives me 1.88 seconds with costs of 15.

Good thing you made me re-measure :) That makes 13 my new bcrypt default.

Considered to low by...?

Reply on news.ycombinator.com