prosody/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/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

-- TODO Rename? Split out subroutines?
-- Also, this is probably openssl specific, what TODO about that?
function genx509san(hosts, config, certhosts, raw) -- recive config through that or some better way?
	local function utf8string(s)
		-- This is how we tell openssl not to encode UTF-8 strings as Latin1
		return s_format("FORMAT:UTF8,UTF8:%s", s);
	end

	local function ia5string(s)
		return s_format("IA5STRING:%s", s);
	end

	local function dnsname(t, host)
		t_insert(t.DNS, idna_to_ascii(host));
	end

	local function srvname(t, host, service)
		t_insert(t.otherName, s_format("%s;%s", oid_dnssrv, ia5string("_" .. service .."." .. idna_to_ascii(host))));
	end

	local function xmppAddr(t, host)
		t_insert(t.otherName, s_format("%s;%s", oid_xmppaddr, utf8string(host)));
	end

	-----------------------------

	local san = {
		DNS = {};
		otherName = {};
	};

	local sslsanconf = { };

	for i = 1,#certhosts do
		local certhost = certhosts[i];
		for name, host in pairs(hosts) do
			if name == certhost or name:sub(-1-#certhost) == "."..certhost then
				dnsname(san, name);
				--print(name .. "#component_module: " .. (config.get(name, "core", "component_module") or "nil"));
				if config.get(name, "core", "component_module") == nil then
					srvname(san, name, "xmpp-client");
				end
				--print(name .. "#anonymous_login: " .. tostring(config.get(name, "core", "anonymous_login")));
				if not (config.get(name, "core", "anonymous_login") or
						config.get(name, "core", "authentication") == "anonymous") then
					srvname(san, name, "xmpp-server");
				end
				xmppAddr(san, name);
			end
		end
	end

	for t, n in pairs(san) do
		for i = 1,#n do
			t_insert(sslsanconf, s_format("%s.%d = %s", t, i -1, n[i]));
		end
	end

	return raw and sslsanconf or t_concat(sslsanconf, "\n");
end

function baseconf()
	return {
		req = {
			distinguished_name = "distinguished_name",
			req_extensions = "v3_extensions",
			x509_extensions = "v3_extensions",
			prompt = "no",
		},
		distinguished_name = {
			commonName = "example.com",
			countryName = "GB",
			localityName = "The Internet",
			organizationName = "Your Organisation",
			organizationalUnitName = "XMPP Department",
			emailAddress = "xmpp@example.com",
		},
		v3_extensions = {
			basicConstraints = "CA:FALSE",
			keyUsage = "digitalSignature,keyEncipherment",
			extendedKeyUsage = "serverAuth,clientAuth",
			subjectAltName = "@subject_alternative_name",
		},
		subject_alternative_name = { },
	}
end

function serialize_conf(conf)
	local s = "";
	for k, t in pairs(conf) do
		s = s .. ("[%s]\n"):format(k);
		if t[1] then
			for i, v in ipairs(t) do
				s = s .. ("%s\n"):format(v);
			end
		else
			for k, v in pairs(t) do
				s = s .. ("%s = %s\n"):format(k, v);
			end
		end
		s = s .. "\n";
	end
	return s;
end

return _M;