util/x509.lua

-- 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/draft-saintandre-tls-server-id-check-10

-- [XMPP-CORE] - http://tools.ietf.org/html/draft-ietf-xmpp-3920bis-18

-- [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");

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 4.4.1 and 4.4.2 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] 4.3, 4.4.4, "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] 1.5, 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] 4.4.4, 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;