File

util/x509.lua @ 5915:e6fed1d80116

Back out 1b0ac7950129, as SSLv3 appears to still be in moderate use on the network. Also, although obsolete, SSLv3 isn't documented to have any weaknesses that TLS 1.0 (the most common version used today) doesn't also have. Get your act together clients!
author Matthew Wild <mwild1@gmail.com>
date Tue, 12 Nov 2013 02:13:01 +0000
parent 4825:5fdc36bd866c
child 5845:c48f717c2fd6
line wrap: on
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-- Prosody IM
-- Copyright (C) 2010 Matthew Wild
-- Copyright (C) 2010 Paul Aurich
--
-- This project is MIT/X11 licensed. Please see the
-- COPYING file in the source package for more information.
--

-- TODO: I feel a fair amount of this logic should be integrated into Luasec,
-- so that everyone isn't re-inventing the wheel.  Dependencies on
-- IDN libraries complicate that.


-- [TLS-CERTS] - http://tools.ietf.org/html/rfc6125
-- [XMPP-CORE] - http://tools.ietf.org/html/rfc6120
-- [SRV-ID]    - http://tools.ietf.org/html/rfc4985
-- [IDNA]      - http://tools.ietf.org/html/rfc5890
-- [LDAP]      - http://tools.ietf.org/html/rfc4519
-- [PKIX]      - http://tools.ietf.org/html/rfc5280

local nameprep = require "util.encodings".stringprep.nameprep;
local idna_to_ascii = require "util.encodings".idna.to_ascii;
local log = require "util.logger".init("x509");
local pairs, ipairs = pairs, ipairs;
local s_format = string.format;
local t_insert = table.insert;
local t_concat = table.concat;

module "x509"

local oid_commonname = "2.5.4.3"; -- [LDAP] 2.3
local oid_subjectaltname = "2.5.29.17"; -- [PKIX] 4.2.1.6
local oid_xmppaddr = "1.3.6.1.5.5.7.8.5"; -- [XMPP-CORE]
local oid_dnssrv   = "1.3.6.1.5.5.7.8.7"; -- [SRV-ID]

-- Compare a hostname (possibly international) with asserted names
-- extracted from a certificate.
-- This function follows the rules laid out in
-- sections 6.4.1 and 6.4.2 of [TLS-CERTS]
--
-- A wildcard ("*") all by itself is allowed only as the left-most label
local function compare_dnsname(host, asserted_names)
	-- TODO: Sufficient normalization?  Review relevant specs.
	local norm_host = idna_to_ascii(host)
	if norm_host == nil then
		log("info", "Host %s failed IDNA ToASCII operation", host)
		return false
	end

	norm_host = norm_host:lower()

	local host_chopped = norm_host:gsub("^[^.]+%.", "") -- everything after the first label

	for i=1,#asserted_names do
		local name = asserted_names[i]
		if norm_host == name:lower() then
			log("debug", "Cert dNSName %s matched hostname", name);
			return true
		end

		-- Allow the left most label to be a "*"
		if name:match("^%*%.") then
			local rest_name = name:gsub("^[^.]+%.", "")
			if host_chopped == rest_name:lower() then
				log("debug", "Cert dNSName %s matched hostname", name);
				return true
			end
		end
	end

	return false
end

-- Compare an XMPP domain name with the asserted id-on-xmppAddr
-- identities extracted from a certificate.  Both are UTF8 strings.
--
-- Per [XMPP-CORE], matches against asserted identities don't include
-- wildcards, so we just do a normalize on both and then a string comparison
--
-- TODO: Support for full JIDs?
local function compare_xmppaddr(host, asserted_names)
	local norm_host = nameprep(host)

	for i=1,#asserted_names do
		local name = asserted_names[i]

		-- We only want to match against bare domains right now, not
		-- those crazy full-er JIDs.
		if name:match("[@/]") then
			log("debug", "Ignoring xmppAddr %s because it's not a bare domain", name)
		else
			local norm_name = nameprep(name)
			if norm_name == nil then
				log("info", "Ignoring xmppAddr %s, failed nameprep!", name)
			else
				if norm_host == norm_name then
					log("debug", "Cert xmppAddr %s matched hostname", name)
					return true
				end
			end
		end
	end

	return false
end

-- Compare a host + service against the asserted id-on-dnsSRV (SRV-ID)
-- identities extracted from a certificate.
--
-- Per [SRV-ID], the asserted identities will be encoded in ASCII via ToASCII.
-- Comparison is done case-insensitively, and a wildcard ("*") all by itself
-- is allowed only as the left-most non-service label.
local function compare_srvname(host, service, asserted_names)
	local norm_host = idna_to_ascii(host)
	if norm_host == nil then
		log("info", "Host %s failed IDNA ToASCII operation", host);
		return false
	end

	-- Service names start with a "_"
	if service:match("^_") == nil then service = "_"..service end

	norm_host = norm_host:lower();
	local host_chopped = norm_host:gsub("^[^.]+%.", "") -- everything after the first label

	for i=1,#asserted_names do
		local asserted_service, name = asserted_names[i]:match("^(_[^.]+)%.(.*)");
		if service == asserted_service then
			if norm_host == name:lower() then
				log("debug", "Cert SRVName %s matched hostname", name);
				return true;
			end

			-- Allow the left most label to be a "*"
			if name:match("^%*%.") then
				local rest_name = name:gsub("^[^.]+%.", "")
				if host_chopped == rest_name:lower() then
					log("debug", "Cert SRVName %s matched hostname", name)
					return true
				end
			end
			if norm_host == name:lower() then
				log("debug", "Cert SRVName %s matched hostname", name);
				return true
			end
		end
	end

	return false
end

function verify_identity(host, service, cert)
	local ext = cert:extensions()
	if ext[oid_subjectaltname] then
		local sans = ext[oid_subjectaltname];

		-- Per [TLS-CERTS] 6.3, 6.4.4, "a client MUST NOT seek a match for a
		-- reference identifier if the presented identifiers include a DNS-ID
		-- SRV-ID, URI-ID, or any application-specific identifier types"
		local had_supported_altnames = false

		if sans[oid_xmppaddr] then
			had_supported_altnames = true
			if compare_xmppaddr(host, sans[oid_xmppaddr]) then return true end
		end

		if sans[oid_dnssrv] then
			had_supported_altnames = true
			-- Only check srvNames if the caller specified a service
			if service and compare_srvname(host, service, sans[oid_dnssrv]) then return true end
		end

		if sans["dNSName"] then
			had_supported_altnames = true
			if compare_dnsname(host, sans["dNSName"]) then return true end
		end

		-- We don't need URIs, but [TLS-CERTS] is clear.
		if sans["uniformResourceIdentifier"] then
			had_supported_altnames = true
		end

		if had_supported_altnames then return false end
	end

	-- Extract a common name from the certificate, and check it as if it were
	-- a dNSName subjectAltName (wildcards may apply for, and receive,
	-- cat treats)
	--
	-- Per [TLS-CERTS] 1.8, a CN-ID is the Common Name from a cert subject
	-- which has one and only one Common Name
	local subject = cert:subject()
	local cn = nil
	for i=1,#subject do
		local dn = subject[i]
		if dn["oid"] == oid_commonname then
			if cn then
				log("info", "Certificate has multiple common names")
				return false
			end

			cn = dn["value"];
		end
	end

	if cn then
		-- Per [TLS-CERTS] 6.4.4, follow the comparison rules for dNSName SANs.
		return compare_dnsname(host, { cn })
	end

	-- If all else fails, well, why should we be any different?
	return false
end

return _M;