3 ms·

The answer depends on the tuning parameters used for the bcrypt hashing (cost/work factor) and the length of the user password. Obviously a 1-character password

The answer depends on the tuning parameters used for the bcrypt hashing (cost/work factor) and the length of the user password. Obviously a 1-character password will fall even with a high workfactor and a dictionary word will probably fall as well. This paper http://www.emsec.rub.de/media/crypto/veroeffentlichungen/2014/10/22/reconfig14_bcrypt.pdf http://www.emsec.rub.de/media/crypto/veroeffentlichungen/201... tags some numbers on breaking passwords with a low cost factor. Assuming a cost factor if 5 (12 would be more "real" world) and an 8 character password with an alphabet of 62 chars (uppercase, lowecase, 10 digits) the estimated cost to break a password within a month is in the millions with dedicated hardware designed for brcypt breaking (Fig 5). With a work factor of 12, an 8 character password will not break on EC2.

eridius 12y ago
I knew bcrypt was tunable, and I guess I was hoping someone from Slack would actually pop up and say how their bcrypt was tuned (which I guess means what the cost factor is). But you do have some good info, I wasn't aware of what expected cost factors were and how secure a single password would be at those cost factors. I'm assuming that your "8 character password" is assuming a randomly-generated password. I'm curious what the expected cost would be of breaking a particularly weak one (e.g. a human-generated password, based on dictionary words although perhaps with mnemonic devices or letter/number substitutions). The paper you linked says their hardware computed 6511 passwords per second at a cost factor of 5, and based on the cycle costs listed, I'm thinking it does 52 passwords per second at a cost factor of 12. Assuming a particularly weak password, I don't know how many passwords a brute-forcer would expect to have to try before hitting the correct one.

eridius 12y ago

I knew bcrypt was tunable, and I guess I was hoping someone from Slack would actually pop up and say how their bcrypt was tuned (which I guess means what the cost factor is). But you do have some good info, I wasn't aware of what expected cost factors were and how secure a single password would be at those cost factors. I'm assuming that your "8 character password" is assuming a randomly-generated password. I'm curious what the expected cost would be of breaking a particularly weak one (e.g. a human-generated password, based on dictionary words although perhaps with mnemonic devices or letter/number substitutions). The paper you linked says their hardware computed 6511 passwords per second at a cost factor of 5, and based on the cycle costs listed, I'm thinking it does 52 passwords per second at a cost factor of 12. Assuming a particularly weak password, I don't know how many passwords a brute-forcer would expect to have to try before hitting the correct one.