[NSE] cccam-version.nse makes use of the new 'formulas' library.

scripts/cccam-version.nse

@@ -2,6 +2,7 @@ local bin = require "bin"
 local nmap = require "nmap"
 local shortport = require "shortport"
 local string = require "string"
+local formulas = require "formulas"
 
 description = [[
 Detects the CCcam service (software for sharing subscription TV among
@@ -19,81 +20,6 @@ categories = {"version"}
 
 author = "David Fifield"
 
-
--- A chi-square test for the null hypothesis that the members of data are drawn
--- from a uniform distribution over num_cats categories.
-local function chi2(data, num_cats)
-	local bins = {}
-	local x2, delta, expected
-
-	for _, x in ipairs(data) do
-		bins[x] = bins[x] or 0
-		bins[x] = bins[x] + 1
-	end
-
-	expected = #data / num_cats
-	x2 = 0.0
-	for _, n in pairs(bins) do
-		delta = n - expected
-		x2 = x2 + delta * delta
-	end
-	x2 = x2 / expected
-
-	return x2
-end
-
--- Split a string into a sequence of bit strings of the given length.
--- splitbits("abc", 5) --> {"01100", "00101", "10001", "00110"}
--- Any short final group is omitted.
-local function splitbits(s, n)
-	local seq
-
-	local _, bits = bin.unpack("B" .. #s, s)
-	seq = {}
-	for i = 1, #bits - n, n do
-		seq[#seq + 1] = bits:sub(i, i + n - 1)
-	end
-
-	return seq
-end
-
--- chi-square cdf table at 0.95 confidence for different degrees of freedom.
--- >>> import scipy.stats, scipy.optimize
--- >>> scipy.optimize.newton(lambda x: scipy.stats.chi2(dof).cdf(x) - 0.95, dof)
-local CHI2_CDF = {
-	[3] = 7.8147279032511738,
-	[15] = 24.99579013972863,
-	[255] = 293.2478350807001,
-}
-
-local function looks_random(data)
-	local x2
-
-	-- Because our sample is so small (only 16 bytes), do a chi-square
-	-- goodness of fit test across groups of 2, 4, and 8 bits. If using only
-	-- 8 bits, for example, any sample whose bytes are all different would
-	-- pass the test. Using 2 bits will tend to catch things like pure
-	-- ASCII, where one out of every four samples never has its high bit
-	-- set.
-
-	x2 = chi2(splitbits(data, 2), 4)
-	if x2 > CHI2_CDF[3] then
-		return false
-	end
-
-	x2 = chi2(splitbits(data, 4), 16)
-	if x2 > CHI2_CDF[15] then
-		return false
-	end
-
-	x2 = chi2({string.byte(data, 1, -1)}, 256)
-	if x2 > CHI2_CDF[255] then
-		return false
-	end
-
-	return true
-end
-
 local NUM_TRIALS = 2
 
 local function trial(host, port)
@@ -127,7 +53,7 @@ function action(host, port)
 		local data
 
 		data = trial(host, port)
-		if not data or seen[data] or #data ~= 16 or not looks_random(data) then
+		if not data or seen[data] or #data ~= 16 or not formulas.looksRandom(data) then
 			return
 		end
 		seen[data] = true