gauth.lua

local sha1 = require "sha1"
local basexx = require "basexx"
local band = bit.band


local GAuth = {}

function GAuth.GenCode(skey, value)
	skey = basexx.from_base32(skey)
	value = string.char(
	0, 0, 0, 0,
	band(value, 0xFF000000) / 0x1000000,
	band(value, 0xFF0000) / 0x10000,
	band(value, 0xFF00) / 0x100,
	band(value, 0xFF))
	local hash = sha1.hmac_binary(skey, value)
	local offset = band(hash:sub(-1):byte(1, 1), 0xF)
	local function bytesToInt(a,b,c,d)
		return a*0x1000000 + b*0x10000 + c*0x100 + d
	end
	hash = bytesToInt(hash:byte(offset + 1, offset + 4))
	hash = band(hash, 0x7FFFFFFF) % 1000000
	return ("%06d"):format(hash)
end

function GAuth.Check(skey, value)
	local base = math.floor(os.time() / 30)
	if GAuth.GenCode(skey, base) == value then return true end
	if GAuth.GenCode(skey, base - 1) == value then return true end
	if GAuth.GenCode(skey, base + 1) == value then return true end
	return false
end

return GAuth