_M = {}
local url = require("url")
local utils = require("utils")
local cookie = require("cookie")
local json = require("json")
local sha = require("sha")
local randbytes = require("randbytes")
local argon2 = require("argon2")
local pow_difficulty = tonumber(os.getenv("POW_DIFFICULTY") or 18)
local pow_kb = tonumber(os.getenv("POW_KB") or 6000)
local pow_time = tonumber(os.getenv("POW_TIME") or 1)
argon2.t_cost(pow_time)
argon2.m_cost(pow_kb)
argon2.parallelism(1)
argon2.hash_len(32)
argon2.variant(argon2.variants.argon2_id)
-- Testing only
-- require("socket")
-- require("print_r")
local captcha_secret = os.getenv("HCAPTCHA_SECRET") or os.getenv("RECAPTCHA_SECRET")
local captcha_sitekey = os.getenv("HCAPTCHA_SITEKEY") or os.getenv("RECAPTCHA_SITEKEY")
local captcha_cookie_secret = os.getenv("CAPTCHA_COOKIE_SECRET")
local pow_cookie_secret = os.getenv("POW_COOKIE_SECRET")
local hmac_cookie_secret = os.getenv("HMAC_COOKIE_SECRET")
local ray_id = os.getenv("RAY_ID")
local captcha_map = Map.new("/etc/haproxy/ddos.map", Map._str);
local captcha_provider_domain = ""
local captcha_classname = ""
local captcha_script_src = ""
local captcha_siteverify_path = ""
local captcha_backend_name = ""
if os.getenv("HCAPTCHA_SITEKEY") then
captcha_provider_domain = "hcaptcha.com"
captcha_classname = "h-captcha"
captcha_script_src = "https://hcaptcha.com/1/api.js"
captcha_siteverify_path = "/siteverify"
captcha_backend_name = "hcaptcha"
else
captcha_provider_domain = "www.google.com"
captcha_classname = "g-recaptcha"
captcha_script_src = "https://www.google.com/recaptcha/api.js"
captcha_siteverify_path = "/recaptcha/api/siteverify"
captcha_backend_name = "recaptcha"
end
function _M.setup_servers()
if pow_difficulty < 8 then
error("POW_DIFFICULTY must be > 8. Around 16-32 is better")
end
local backend_name = os.getenv("BACKEND_NAME")
local server_prefix = os.getenv("SERVER_PREFIX")
if backend_name == nil or server_prefix == nil then
return;
end
local hosts_map = Map.new("/etc/haproxy/hosts.map", Map._str);
local handle = io.open("/etc/haproxy/hosts.map", "r")
local line = handle:read("*line")
local counter = 1
while line do
local domain, backend_host = line:match("([^%s]+)%s+([^%s]+)")
local port_index = backend_host:match'^.*():'
local backend_hostname = backend_host:sub(0, port_index-1)
local backend_port = backend_host:sub(port_index + 1)
core.set_map("/etc/haproxy/backends.map", domain, server_prefix..counter)
local proxy = core.proxies[backend_name].servers[server_prefix..counter]
proxy:set_addr(backend_hostname, backend_port)
proxy:set_ready()
line = handle:read("*line")
counter = counter + 1
end
handle:close()
end
-- main page template
local body_template = [[
Hold on...
%s
%s
%s
]]
local noscript_extra_template = [[
No JavaScript?
Run this in a linux terminal (requires argon2 package installed):
]]
-- title with favicon and hostname
local site_name_section_template = [[
%s
]]
-- spinner animation for proof of work
local pow_section_template = [[
Checking your browser for robots 🤖
]]
-- message, captcha form and submit button
local captcha_section_template = [[
Please solve the captcha to continue.
]]
-- kill a tor circuit
function _M.kill_tor_circuit(txn)
local ip = txn.sf:src()
if ip:sub(1,19) ~= "fc00:dead:beef:4dad" then
return -- not a tor circuit id/ip. we shouldn't get here, but just in case.
end
-- split the IP, take the last 2 sections
local split_ip = utils.split(ip, ":")
local aa_bb = split_ip[5] or "0000"
local cc_dd = split_ip[6] or "0000"
aa_bb = string.rep("0", 4 - #aa_bb) .. aa_bb
cc_dd = string.rep("0", 4 - #cc_dd) .. cc_dd
-- convert the last 2 sections to a number from hex, which makes the circuit ID
local circuit_identifier = tonumber(aa_bb..cc_dd, 16)
print('Closing Tor circuit ID: '..circuit_identifier..', "IP": '..ip)
utils.send_tor_control_port(circuit_identifier)
end
function _M.view(applet)
-- set response body and declare status code
local response_body = ""
local response_status_code
-- if request is GET, serve the challenge page
if applet.method == "GET" then
-- get the user_key#challenge#sig
local user_key = sha.bin_to_hex(randbytes(16))
local challenge_hash = utils.generate_secret(applet, pow_cookie_secret, user_key, true)
local signature = sha.hmac(sha.sha3_256, hmac_cookie_secret, user_key .. challenge_hash)
local combined_challenge = user_key .. "#" .. challenge_hash .. "#" .. signature
-- define body sections
local site_name_body = ""
local captcha_body = ""
local pow_body = ""
local noscript_extra_body = ""
-- check if captcha is enabled, path+domain priority, then just domain, and 0 otherwise
local captcha_enabled = false
local host = applet.headers['host'][0]
local path = applet.qs; --because on /bot-check?/whatever, .qs (query string) holds the "path"
local captcha_map_lookup = captcha_map:lookup(host..path) or captcha_map:lookup(host) or 0
captcha_map_lookup = tonumber(captcha_map_lookup)
if captcha_map_lookup == 2 then
captcha_enabled = true
end
-- pow at least is always enabled when reaching bot-check page
site_name_body = string.format(site_name_section_template, host)
if captcha_enabled then
captcha_body = string.format(captcha_section_template, captcha_classname,
captcha_sitekey, captcha_script_src)
else
pow_body = pow_section_template
noscript_extra_body = string.format(noscript_extra_template, user_key, challenge_hash, signature,
math.ceil(pow_difficulty/8), pow_time, pow_kb)
end
-- sub in the body sections
response_body = string.format(body_template, combined_challenge,
pow_difficulty, pow_time, pow_kb,
site_name_body, pow_body, captcha_body, noscript_extra_body, ray_id)
response_status_code = 403
-- if request is POST, check the answer to the pow/cookie
elseif applet.method == "POST" then
-- if they fail, set a var for use in ACLs later
local valid_submission = false
-- parsed POST body
local parsed_body = url.parseQuery(applet.receive(applet))
-- whether to set cookies sent as secure or not
local secure_cookie_flag = " Secure=true;"
if applet.sf:ssl_fc() == "0" then
secure_cookie_flag = ""
end
-- handle setting the POW cookie
local user_pow_response = parsed_body["pow_response"]
if user_pow_response then
-- split the response up (makes the nojs submission easier because it can be a single field)
local split_response = utils.split(user_pow_response, "#")
if #split_response == 4 then
local given_user_key = split_response[1]
local given_challenge_hash = split_response[2]
local given_signature = split_response[3]
local given_answer = split_response[4]
-- regenerate the challenge and compare it
local generated_challenge_hash = utils.generate_secret(applet, pow_cookie_secret, given_user_key, true)
if given_challenge_hash == generated_challenge_hash then
-- regenerate the signature and compare it
local generated_signature = sha.hmac(sha.sha3_256, hmac_cookie_secret, given_user_key .. given_challenge_hash)
if given_signature == generated_signature then
-- do the work with their given answer
local full_hash = argon2.hash_encoded(given_challenge_hash .. given_answer, given_user_key)
-- check the output is correct
local hash_output = utils.split(full_hash, '$')[6]:sub(0, 43) -- https://github.com/thibaultcha/lua-argon2/issues/37
local hex_hash_output = sha.bin_to_hex(sha.base64_to_bin(hash_output));
if utils.checkdiff(hex_hash_output, pow_difficulty) then
-- the answer was good, give them a cookie
local signature = sha.hmac(sha.sha3_256, hmac_cookie_secret, given_user_key .. given_challenge_hash .. given_answer)
local combined_cookie = given_user_key .. "#" .. given_challenge_hash .. "#" .. given_answer .. "#" .. signature
applet:add_header(
"set-cookie",
string.format(
"z_ddos_pow=%s; Expires=Thu, 31-Dec-37 23:55:55 GMT; Path=/; Domain=.%s; SameSite=Strict;%s",
combined_cookie,
applet.headers['host'][0],
secure_cookie_flag
)
)
valid_submission = true
end
end
end
end
end
-- handle setting the captcha cookie
local user_captcha_response = parsed_body["h-captcha-response"] or parsed_body["g-recaptcha-response"]
if valid_submission and user_captcha_response then -- only check captcha if POW is already correct
-- format the url for verifying the captcha response
local captcha_url = string.format(
"https://%s%s",
core.backends[captcha_backend_name].servers[captcha_backend_name]:get_addr(),
captcha_siteverify_path
)
-- construct the captcha body to send to the captcha url
local captcha_body = url.buildQuery({
secret=captcha_secret,
response=user_captcha_response
})
-- instantiate an http client and make the request
local httpclient = core.httpclient()
local res = httpclient:post{
url=captcha_url,
body=captcha_body,
headers={
[ "host" ] = { captcha_provider_domain },
[ "content-type" ] = { "application/x-www-form-urlencoded" }
}
}
-- try parsing the response as json
local status, api_response = pcall(json.decode, res.body)
if not status then
api_response = {}
end
-- the response was good i.e the captcha provider says they passed, give them a cookie
if api_response.success == true then
local user_key = sha.bin_to_hex(randbytes(16))
local user_hash = utils.generate_secret(applet, captcha_cookie_secret, user_key, true)
local signature = sha.hmac(sha.sha3_256, hmac_cookie_secret, user_key .. user_hash)
local combined_cookie = user_key .. "#" .. user_hash .. "#" .. signature
applet:add_header(
"set-cookie",
string.format(
"z_ddos_captcha=%s; Expires=Thu, 31-Dec-37 23:55:55 GMT; Path=/; Domain=.%s; SameSite=Strict;%s",
combined_cookie,
applet.headers['host'][0],
secure_cookie_flag
)
)
valid_submission = valid_submission and true
end
end
if not valid_submission then
_M.kill_tor_circuit(applet)
end
-- redirect them to their desired page in applet.qs (query string)
-- if they didn't get the appropriate cookies they will be sent back to the challenge page
response_status_code = 302
applet:add_header("location", applet.qs)
-- else if its another http method, just 403 them
else
response_status_code = 403
end
-- finish sending the response
applet:set_status(response_status_code)
applet:add_header("content-type", "text/html; charset=utf-8")
applet:add_header("content-length", string.len(response_body))
applet:start_response()
applet:send(response_body)
end
-- check if captcha is enabled, path+domain priority, then just domain, and 0 otherwise
function _M.decide_checks_necessary(txn)
local host = txn.sf:hdr("Host")
local path = txn.sf:path();
local captcha_map_lookup = captcha_map:lookup(host..path) or captcha_map:lookup(host) or 0
captcha_map_lookup = tonumber(captcha_map_lookup)
if captcha_map_lookup == 1 then
txn:set_var("txn.validate_pow", true)
elseif captcha_map_lookup == 2 then
txn:set_var("txn.validate_captcha", true)
txn:set_var("txn.validate_pow", true)
end
-- otherwise, domain+path was set to 0 (whitelist) or there is no entry in the map
end
-- check if captcha cookie is valid, separate secret from POW
function _M.check_captcha_status(txn)
local parsed_request_cookies = cookie.get_cookie_table(txn.sf:hdr("Cookie"))
local received_captcha_cookie = parsed_request_cookies["z_ddos_captcha"] or ""
-- split the cookie up
local split_cookie = utils.split(received_captcha_cookie, "#")
if #split_cookie ~= 3 then
return
end
local given_user_key = split_cookie[1]
local given_user_hash = split_cookie[2]
local given_signature = split_cookie[3]
-- regenerate the user hash and compare it
local generated_user_hash = utils.generate_secret(txn, captcha_cookie_secret, given_user_key, false)
if generated_user_hash ~= given_user_hash then
return
end
-- regenerate the signature and compare it
local generated_signature = sha.hmac(sha.sha3_256, hmac_cookie_secret, given_user_key .. given_user_hash)
if given_signature == generated_signature then
return txn:set_var("txn.captcha_passed", true)
end
end
-- check if pow cookie is valid
function _M.check_pow_status(txn)
local parsed_request_cookies = cookie.get_cookie_table(txn.sf:hdr("Cookie"))
local received_pow_cookie = parsed_request_cookies["z_ddos_pow"] or ""
-- split the cookie up
local split_cookie = utils.split(received_pow_cookie, "#")
if #split_cookie ~= 4 then
return
end
local given_user_key = split_cookie[1]
local given_challenge_hash = split_cookie[2]
local given_answer = split_cookie[3]
local given_signature = split_cookie[4]
-- regenerate the challenge and compare it
local generated_challenge_hash = utils.generate_secret(txn, pow_cookie_secret, given_user_key, false)
if given_challenge_hash ~= generated_challenge_hash then
return
end
-- regenerate the signature and compare it
local generated_signature = sha.hmac(sha.sha3_256, hmac_cookie_secret, given_user_key .. given_challenge_hash .. given_answer)
if given_signature == generated_signature then
return txn:set_var("txn.pow_passed", true)
end
end
return _M