-- 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.

--=========================

--SASL DIGEST-MD5 according to RFC 2831

local function sasl_mechanism_digest_md5(self, message)

	--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)

		local message = {}

		for k, v in gmatch(data, [[([%w%-]+)="?([^",]*)"?,?]]) do -- FIXME The hacky regex makes me shudder

			message[k] = v;

		end

		return message;

	end

	if not self.nonce then

		self.nonce = generate_uuid();

		self.step = 0;

		self.nonce_count = {};

	end

	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