The scrypt key derivation function is designed to be far more secure against hardware brute-force attacks than alternative functions such as PBKDF2 or bcrypt.
Why you should use scrypt
The designers of scrypt estimate that on modern (2009) hardware, if 5 seconds are spent computing a derived key, the cost of a hardware brute-force attack against scrypt is roughly 4000 times greater than the cost of a similar attack against bcrypt (to find the same password), and 20000 times greater than a similar attack against PBKDF2.
How to install scrypt
gem install scrypt
How to use scrypt
It works pretty similarly to ruby-bcrypt with a few minor differences, especially where the cost factor is concerned.
require "scrypt" # hash a user's password password = SCrypt::Password.create("my grand secret") # => "400$8$36$78f4ae6983f76119$37ec6ce55a2b928dc56ff9a7d0cdafbd7dbde49d9282c38a40b1434e88f24cf5" # compare to strings password == "my grand secret" # => true password == "a paltry guess" # => false
Password.create takes five options which will determine the key length and salt size, as well as the cost limits of the computation:
:key_lenspecifies the length in bytes of the key you want to generate. The default is 32 bytes (256 bits). Minimum is 16 bytes (128 bits). Maximum is 512 bytes (4096 bits).
:salt_sizespecifies the size in bytes of the random salt you want to generate. The default and maximum is 32 bytes (256 bits). Minimum is 8 bytes (64 bits).
:max_timespecifies the maximum number of seconds the computation should take.
:max_memspecifies the maximum number of bytes the computation should take. A value of 0 specifies no upper limit. The minimum is always 1 MB.
:max_memfracspecifies the maximum memory in a fraction of available resources to use. Any value equal to 0 or greater than 0.5 will result in 0.5 being used.
:costspecifies a cost string (e.g.
'400$8$19$') from the
:max_*options will be ignored if this option is given, or if
calibrate!has been called.
Default options will result in calculation time of approx. 200 ms with 16 MB memory use.
Other things you can do
require "scrypt" SCrypt::Engine.calibrate # => "400$8$25$" salt = SCrypt::Engine.generate_salt # => "400$8$26$b62e0f787a5fc373" SCrypt::Engine.hash_secret "my grand secret", salt # => "400$8$26$b62e0f787a5fc373$0399ccd4fa26642d92741b17c366b7f6bd12ccea5214987af445d2bed97bc6a2" SCrypt::Engine.calibrate!(max_mem: 16 * 1024 * 1024) # => "4000$8$4$" SCrypt::Engine.generate_salt # => "4000$8$4$c6d101522d3cb045"
Usage in Rails (and the like)
# store it safely in the user model user.update_attribute(:password, SCrypt::Password.create("my grand secret")) # read it back later user.reload! password = SCrypt::Password.new(user.password) password == "my grand secret" # => true