util/sasl.lua

-- sasl.lua v0.4
-- Copyright (C) 2008-2009 Tobias Markmann
--
--    All rights reserved.
--
--    Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met:
--
--        * Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer.
--        * Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution.
--        * Neither the name of Tobias Markmann nor the names of its contributors may be used to endorse or promote products derived from this software without specific prior written permission.
--
--    THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.


local md5 = require "util.hashes".md5;
local log = require "util.logger".init("sasl");
local tostring = tostring;
local st = require "util.stanza";
local generate_uuid = require "util.uuid".generate;
local t_insert, t_concat = table.insert, table.concat;
local to_byte, to_char = string.byte, string.char;
local to_unicode = require "util.encodings".idna.to_unicode;
local s_match = string.match;
local gmatch = string.gmatch
local string = string
local math = require "math"
local type = type
local error = error
local print = print

module "sasl"

-- Credentials handler:
--   Arguments: ("PLAIN", user, host, password)
--   Returns: true (success) | false (fail) | nil (user unknown)
local function new_plain(realm, credentials_handler)
	local object = { mechanism = "PLAIN", realm = realm, credentials_handler = credentials_handler}
	function object.feed(self, message)
		if message == "" or message == nil then return "failure", "malformed-request" end
		local response = message
		local authorization = s_match(response, "([^&%z]+)")
		local authentication = s_match(response, "%z([^&%z]+)%z")
		local password = s_match(response, "%z[^&%z]+%z([^&%z]+)")

    if authentication == nil or password == nil then return "failure", "malformed-request" end
    self.username = authentication
    local auth_success = self.credentials_handler("PLAIN", self.username, self.realm, password)

    if auth_success then
      return "success"
    elseif auth_success == nil then
      return "failure", "account-disabled"
    else
      return "failure", "not-authorized"
    end
  end
  return object
end

-- credentials_handler:
--   Arguments: (mechanism, node, domain, realm, decoder)
--   Returns: Password encoding, (plaintext) password
-- implementing RFC 2831
local function new_digest_md5(realm, credentials_handler)
	--TODO complete support for authzid

	local function serialize(message)
		local data = ""

		if type(message) ~= "table" then error("serialize needs an argument of type table.") end

		-- testing all possible values
		if message["realm"] then data = data..[[realm="]]..message.realm..[[",]] end
		if message["nonce"] then data = data..[[nonce="]]..message.nonce..[[",]] end
		if message["qop"] then data = data..[[qop="]]..message.qop..[[",]] end
		if message["charset"] then data = data..[[charset=]]..message.charset.."," end
		if message["algorithm"] then data = data..[[algorithm=]]..message.algorithm.."," end
		if message["rspauth"] then data = data..[[rspauth=]]..message.rspauth.."," end
		data = data:gsub(",$", "")
		return data
	end

	local function utf8tolatin1ifpossible(passwd)
		local i = 1;
		while i <= #passwd do
			local passwd_i = to_byte(passwd:sub(i, i));
			if passwd_i > 0x7F then
				if passwd_i < 0xC0 or passwd_i > 0xC3 then
					return passwd;
				end
				i = i + 1;
				passwd_i = to_byte(passwd:sub(i, i));
				if passwd_i < 0x80 or passwd_i > 0xBF then
					return passwd;
				end
			end
			i = i + 1;
		end

		local p = {};
		local j = 0;
		i = 1;
		while (i <= #passwd) do
			local passwd_i = to_byte(passwd:sub(i, i));
			if passwd_i > 0x7F then
				i = i + 1;
				local passwd_i_1 = to_byte(passwd:sub(i, i));
				t_insert(p, to_char(passwd_i%4*64 + passwd_i_1%64)); -- I'm so clever
			else
				t_insert(p, to_char(passwd_i));
			end
			i = i + 1;
		end
		return t_concat(p);
	end
	local function latin1toutf8(str)
		local p = {};
		for ch in gmatch(str, ".") do
			ch = to_byte(ch);
			if (ch < 0x80) then
				t_insert(p, to_char(ch));
			elseif (ch < 0xC0) then
				t_insert(p, to_char(0xC2, ch));
			else
				t_insert(p, to_char(0xC3, ch - 64));
			end
		end
		return t_concat(p);
	end
	local function parse(data)
		message = {}
		for k, v in gmatch(data, [[([%w%-]+)="?([^",]*)"?,?]]) do -- FIXME The hacky regex makes me shudder
			message[k] = v;
		end
		return message;
	end

	local object = { mechanism = "DIGEST-MD5", realm = realm, credentials_handler = credentials_handler};

	object.nonce = generate_uuid();
	object.step = 0;
	object.nonce_count = {};

	function object.feed(self, message)
		self.step = self.step + 1;
		if (self.step == 1) then
			local challenge = serialize({	nonce = object.nonce,
											qop = "auth",
											charset = "utf-8",
											algorithm = "md5-sess",
											realm = self.realm});
			return "challenge", challenge;
		elseif (self.step == 2) then
			local response = parse(message);
			-- check for replay attack
			if response["nc"] then
				if self.nonce_count[response["nc"]] then return "failure", "not-authorized" end
			end

			-- check for username, it's REQUIRED by RFC 2831
			if not response["username"] then
				return "failure", "malformed-request";
			end
			self["username"] = response["username"];

			-- check for nonce, ...
			if not response["nonce"] then
				return "failure", "malformed-request";
			else
				-- check if it's the right nonce
				if response["nonce"] ~= tostring(self.nonce) then return "failure", "malformed-request" end
			end

			if not response["cnonce"] then return "failure", "malformed-request", "Missing entry for cnonce in SASL message." end
			if not response["qop"] then response["qop"] = "auth" end

			if response["realm"] == nil or response["realm"] == "" then
				response["realm"] = "";
			elseif response["realm"] ~= self.realm then
				return "failure", "not-authorized", "Incorrect realm value";
			end

			local decoder;
			if response["charset"] == nil then
				decoder = utf8tolatin1ifpossible;
			elseif response["charset"] ~= "utf-8" then
				return "failure", "incorrect-encoding", "The client's response uses "..response["charset"].." for encoding with isn't supported by sasl.lua. Supported encodings are latin or utf-8.";
			end

			local domain = "";
			local protocol = "";
			if response["digest-uri"] then
				protocol, domain = response["digest-uri"]:match("(%w+)/(.*)$");
				if protocol == nil or domain == nil then return "failure", "malformed-request" end
			else
				return "failure", "malformed-request", "Missing entry for digest-uri in SASL message."
			end

			--TODO maybe realm support
			self.username = response["username"];
			local password_encoding, Y = self.credentials_handler("DIGEST-MD5", response["username"], self.realm, response["realm"], decoder);
			if Y == nil then return "failure", "not-authorized"
			elseif Y == false then return "failure", "account-disabled" end
			local A1 = "";
			if response.authzid then
				if response.authzid == self.username.."@"..self.realm then
					-- COMPAT
					log("warn", "Client is violating XMPP RFC. See section 6.1 of RFC 3920.");
					A1 = Y..":"..response["nonce"]..":"..response["cnonce"]..":"..response.authzid;
				else
					A1 = "?";
				end
			else
				A1 = Y..":"..response["nonce"]..":"..response["cnonce"];
			end
			local A2 = "AUTHENTICATE:"..protocol.."/"..domain;

			local HA1 = md5(A1, true);
			local HA2 = md5(A2, true);

			local KD = HA1..":"..response["nonce"]..":"..response["nc"]..":"..response["cnonce"]..":"..response["qop"]..":"..HA2;
			local response_value = md5(KD, true);

			if response_value == response["response"] then
				-- calculate rspauth
				A2 = ":"..protocol.."/"..domain;

				HA1 = md5(A1, true);
				HA2 = md5(A2, true);

				KD = HA1..":"..response["nonce"]..":"..response["nc"]..":"..response["cnonce"]..":"..response["qop"]..":"..HA2
				local rspauth = md5(KD, true);
				self.authenticated = true;
				return "challenge", serialize({rspauth = rspauth});
			else
				return "failure", "not-authorized", "The response provided by the client doesn't match the one we calculated."
			end
		elseif self.step == 3 then
			if self.authenticated ~= nil then return "success"
			else return "failure", "malformed-request" end
		end
	end
	return object;
end

-- Credentials handler: Can be nil. If specified, should take the mechanism as
-- the only argument, and return true for OK, or false for not-OK (TODO)
local function new_anonymous(realm, credentials_handler)
	local object = { mechanism = "ANONYMOUS", realm = realm, credentials_handler = credentials_handler}
		function object.feed(self, message)
			return "success"
		end
	object["username"] = generate_uuid()
	return object
end


function new(mechanism, realm, credentials_handler)
	local object
	if mechanism == "PLAIN" then object = new_plain(realm, credentials_handler)
	elseif mechanism == "DIGEST-MD5" then object = new_digest_md5(realm, credentials_handler)
	elseif mechanism == "ANONYMOUS" then object = new_anonymous(realm, credentials_handler)
	else
		log("debug", "Unsupported SASL mechanism: "..tostring(mechanism));
		return nil
	end
	return object
end

return _M;