comm-central/third_party/botan/src/lib/passhash/bcrypt
Name Description Size
bcrypt.cpp On a 4 GHz Skylake, workfactor == 18 takes about 15 seconds to hash a password. This seems like a reasonable upper bound for the time being. Bcrypt allows up to work factor 31 (2^31 iterations) 6269
bcrypt.h Create a password hash using Bcrypt Takes the @p password to hash, a @p rng, and a @p work_factor. The resulting password hash is returned as a string. Higher work factors increase the amount of time the algorithm runs, increasing the cost of cracking attempts. The increase is exponential, so a work factor of 12 takes roughly twice as long as work factor 11. The default work factor was set to 10 up until the 2.8.0 release. It is recommended to set the work factor as high as your system can tolerate (from a performance and latency perspective) since higher work factors greatly improve the security against GPU-based attacks. For example, for protecting high value administrator passwords, consider using work factor 15 or 16; at these work factors each bcrypt computation takes several seconds. Since admin logins will be relatively uncommon, it might be acceptable for each login attempt to take some time. As of 2018, a good password cracking rig (with 8 NVIDIA 1080 cards) can attempt about 1 billion bcrypt computations per month for work factor 13. For work factor 12, it can do twice as many. For work factor 15, it can do only one quarter as many attempts. Due to bugs affecting various implementations of bcrypt, several different variants of the algorithm are defined. As of 2.7.0 Botan supports generating (or checking) the 2a, 2b, and 2y variants. Since Botan has never been affected by any of the bugs which necessitated these version upgrades, all three versions are identical beyond the version identifier. Which variant to use is controlled by the @p version argument. The bcrypt @p work_factor must be at least 4 (though at this work factor bcrypt is not very secure). The bcrypt format allows up to 31, but Botan currently rejects all work factors greater than 18 since even that work factor requires roughly 15 seconds of computation on a fast machine. @warning The password is truncated at at most 72 characters; characters after that do not have any effect on the resulting hash. To support longer passwords, consider pre-hashing the password, for example by using the hex encoding of SHA-256 of the password as the input to bcrypt. @param password the password. @param rng a random number generator @param work_factor how much work to do to slow down guessing attacks @param version which version to emit (may be 'a', 'b', or 'y' all of which have identical behavior in this implementation). @see https://www.usenix.org/events/usenix99/provos/provos_html/ TODO(Botan4) Convert work_factor to a size_t 3660
info.txt 215