kayibea / lua-bcrypt

A bcrypt library for Lua

A Lua wrapper for OpenBSD's bcrypt.

Requirements

lua >= 5.1

Installation

$ luarocks install bcrypt

Usage

local bcrypt = require( "bcrypt" )

-- Bigger numbers here will make your digest exponentially harder to compute
local log_rounds = 9

local digest = bcrypt.digest( "password", log_rounds )
assert( bcrypt.verify( "password", digest ) )

Security concerns

Lua will keep plaintext passwords around in memory as part of its string interning mechanism. As far as I'm aware, there's nothing I can do about this.

Tuning

If you would like to automatically tune the number of rounds to your hardware, you can include a function like:

function bcrypt.tune( t )
	local SAMPLES = 10
	local rounds = 5

	while true do
		local total = 0

		for i = 1, SAMPLES do
			local start = os.clock()
			bcrypt.digest( "asdf", rounds )
			local delta = os.clock() - start

			total = total + delta
		end

		if ( total / SAMPLES ) * 1000 >= t then
			return rounds - 1
		end

		rounds = rounds + 1
	end
end

This function returns the largest load factor such that bcrypt.digest( str, work ) takes less than t milliseconds.