-- sasl.lua v0.4

-- Copyright (C) 2008-2010 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 s_match = string.match;

local type = type

local string = string

local tostring = tostring;

local base64 = require "util.encodings".base64;

local hmac_sha1 = require "util.hmac".sha1;

local sha1 = require "util.hashes".sha1;

local generate_uuid = require "util.uuid".generate;

local saslprep = require "util.encodings".stringprep.saslprep;

local log = require "util.logger".init("sasl");

local t_concat = table.concat;

local char = string.char;

local byte = string.byte;

module "scram"

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

--SASL SCRAM-SHA-1 according to RFC 5802

--[[

Supported Authentication Backends

scram_{MECH}:

	-- MECH being a standard hash name (like those at IANA's hash registry) with '-' replaced with '_'

	function(username, realm)

		return stored_key, server_key, iteration_count, salt, state;

	end

Supported Channel Binding Backends

'tls-unique' according to RFC 5929

]]

local default_i = 4096

local function bp( b )

	local result = ""

	for i=1, b:len() do

		result = result.."\\"..b:byte(i)

	end

	return result

end

local xor_map = {0;1;2;3;4;5;6;7;8;9;10;11;12;13;14;15;1;0;3;2;5;4;7;6;9;8;11;10;13;12;15;14;2;3;0;1;6;7;4;5;10;11;8;9;14;15;12;13;3;2;1;0;7;6;5;4;11;10;9;8;15;14;13;12;4;5;6;7;0;1;2;3;12;13;14;15;8;9;10;11;5;4;7;6;1;0;3;2;13;12;15;14;9;8;11;10;6;7;4;5;2;3;0;1;14;15;12;13;10;11;8;9;7;6;5;4;3;2;1;0;15;14;13;12;11;10;9;8;8;9;10;11;12;13;14;15;0;1;2;3;4;5;6;7;9;8;11;10;13;12;15;14;1;0;3;2;5;4;7;6;10;11;8;9;14;15;12;13;2;3;0;1;6;7;4;5;11;10;9;8;15;14;13;12;3;2;1;0;7;6;5;4;12;13;14;15;8;9;10;11;4;5;6;7;0;1;2;3;13;12;15;14;9;8;11;10;5;4;7;6;1;0;3;2;14;15;12;13;10;11;8;9;6;7;4;5;2;3;0;1;15;14;13;12;11;10;9;8;7;6;5;4;3;2;1;0;};

local result = {};

local function binaryXOR( a, b )

	for i=1, #a do

		local x, y = byte(a, i), byte(b, i);

		local lowx, lowy = x % 16, y % 16;

		local hix, hiy = (x - lowx) / 16, (y - lowy) / 16;

		local lowr, hir = xor_map[lowx * 16 + lowy + 1], xor_map[hix * 16 + hiy + 1];

		local r = hir * 16 + lowr;

		result[i] = char(r)

	end

	return t_concat(result);

end

-- hash algorithm independent Hi(PBKDF2) implementation

function Hi(hmac, str, salt, i)

	local Ust = hmac(str, salt.."\0\0\0\1");

	local res = Ust;

	for n=1,i-1 do

		local Und = hmac(str, Ust)

		res = binaryXOR(res, Und)

		Ust = Und

	end

	return res

end

local function validate_username(username)

	-- check for forbidden char sequences

	for eq in username:gmatch("=(.?.?)") do

		if eq ~= "2D" and eq ~= "3D" then

			return false

		end

	end

	-- replace =2D with , and =3D with =

	username = username:gsub("=2D", ",");

	username = username:gsub("=3D", "=");

	-- apply SASLprep

	username = saslprep(username);

	return username;

end

local function hashprep(hashname)

	return hashname:lower():gsub("-", "_");

end

function getAuthenticationDatabaseSHA1(password, salt, iteration_count)

	if type(password) ~= "string" or type(salt) ~= "string" or type(iteration_count) ~= "number" then

		return false, "inappropriate argument types"

	end

	if iteration_count < 4096 then

		log("warn", "Iteration count < 4096 which is the suggested minimum according to RFC 5802.")

	end

	local salted_password = Hi(hmac_sha1, password, salt, iteration_count);

	local stored_key = sha1(hmac_sha1(salted_password, "Client Key"))

	local server_key = hmac_sha1(salted_password, "Server Key");

	return true, stored_key, server_key

end

local function scram_gen(hash_name, H_f, HMAC_f)

	local function scram_hash(self, message)

		if not self.state then self["state"] = {} end

		local support_channel_binding = false;

		if self.profile.cb then support_channel_binding = true; end

		if type(message) ~= "string" or #message == 0 then return "failure", "malformed-request" end

		if not self.state.name then

			-- we are processing client_first_message

			local client_first_message = message;

			log("debug", client_first_message);

			-- TODO: fail if authzid is provided, since we don't support them yet

			self.state["client_first_message"] = client_first_message;

			self.state["gs2_cbind_flag"], self.state["gs2_cbind_name"], self.state["authzid"], self.state["name"], self.state["clientnonce"]

				= client_first_message:match("^(%a)=?([%a%-]*),(.*),n=(.*),r=([^,]*).*");

			-- check for invalid gs2_flag_type start

			local gs2_flag_type = string.sub(self.state.gs2_cbind_flag, 0, 1)

			if gs2_flag_type ~=  "y" and gs2_flag_type ~=  "n" and gs2_flag_type ~=  "p" then

				return "failure", "malformed-request", "The GS2 header has to start with 'y', 'n', or 'p'."

			end

			if support_channel_binding then

				if string.sub(self.state.gs2_cbind_flag, 0, 1) == "y" then

					return "failure", "malformed-request";

				end

				-- check whether we support the proposed channel binding type

				if not self.profile.cb[self.state.gs2_cbind_name] then

					return "failure", "malformed-request", "Proposed channel binding type isn't supported.";

				end

			else

				-- we don't support channelbinding, 

				if self.state.gs2_cbind_flag ~= "n" and self.state.gs2_cbind_flag ~= "y" then

					return "failure", "malformed-request";

				end

			end

			if not self.state.name or not self.state.clientnonce then

				return "failure", "malformed-request", "Channel binding isn't support at this time.";

			end

			self.state.name = validate_username(self.state.name);

			if not self.state.name then

				log("debug", "Username violates either SASLprep or contains forbidden character sequences.")

				return "failure", "malformed-request", "Invalid username.";

			end

			self.state["servernonce"] = generate_uuid();

			-- retreive credentials

			if self.profile.plain then

				local password, state = self.profile.plain(self, self.state.name, self.realm)

				if state == nil then return "failure", "not-authorized"

				elseif state == false then return "failure", "account-disabled" end

				password = saslprep(password);

				if not password then

					log("debug", "Password violates SASLprep.");

					return "failure", "not-authorized", "Invalid password."

				end

				self.state.salt = generate_uuid();

				self.state.iteration_count = default_i;

				local succ = false;

				succ, self.state.stored_key, self.state.server_key = getAuthenticationDatabaseSHA1(password, self.state.salt, default_i, self.state.iteration_count);

				if not succ then

					log("error", "Generating authentication database failed. Reason: %s", self.state.stored_key);

					return "failure", "temporary-auth-failure";

				end

			elseif self.profile["scram_"..hashprep(hash_name)] then

				local stored_key, server_key, iteration_count, salt, state = self.profile["scram_"..hashprep(hash_name)](self, self.state.name, self.realm);

				if state == nil then return "failure", "not-authorized"

				elseif state == false then return "failure", "account-disabled" end

				self.state.stored_key = stored_key;

				self.state.server_key = server_key;

				self.state.iteration_count = iteration_count;

				self.state.salt = salt

			end

			local server_first_message = "r="..self.state.clientnonce..self.state.servernonce..",s="..base64.encode(self.state.salt)..",i="..self.state.iteration_count;

			self.state["server_first_message"] = server_first_message;

			return "challenge", server_first_message

		else

			-- we are processing client_final_message

			local client_final_message = message;

			log("debug", "client_final_message: %s", client_final_message);

			self.state["channelbinding"], self.state["nonce"], self.state["proof"] = client_final_message:match("^c=(.*),r=(.*),.*p=(.*)");

			if not self.state.proof or not self.state.nonce or not self.state.channelbinding then

				return "failure", "malformed-request", "Missing an attribute(p, r or c) in SASL message.";

			end

			if self.state.gs2_cbind_name then

				-- we support channelbinding, so check if the value is valid

				local client_gs2_header = base64.decode(self.state.channelbinding)

				local our_client_gs2_header = "p="..self.state.gs2_cbind_name..","..self.state["authzid"]..","..self.profile.cb[self.state.gs2_cbind_name](self);

				if client_gs2_header ~= our_client_gs2_header then

					return "failure", "malformed-request", "Invalid channel binding value.";

				end

			end

			if self.state.nonce ~= self.state.clientnonce..self.state.servernonce then

				return "failure", "malformed-request", "Wrong nonce in client-final-message.";

			end

			local ServerKey = self.state.server_key;

			local StoredKey = self.state.stored_key;

			local AuthMessage = "n=" .. s_match(self.state.client_first_message,"n=(.+)") .. "," .. self.state.server_first_message .. "," .. s_match(client_final_message, "(.+),p=.+")

			local ClientSignature = HMAC_f(StoredKey, AuthMessage)

			local ClientKey = binaryXOR(ClientSignature, base64.decode(self.state.proof))

			local ServerSignature = HMAC_f(ServerKey, AuthMessage)

			if StoredKey == H_f(ClientKey) then

				local server_final_message = "v="..base64.encode(ServerSignature);

				self["username"] = self.state.name;

				return "success", server_final_message;

			else

				return "failure", "not-authorized", "The response provided by the client doesn't match the one we calculated.";

			end

		end

	end

	return scram_hash;

end

function init(registerMechanism)

	local function registerSCRAMMechanism(hash_name, hash, hmac_hash)

		registerMechanism("SCRAM-"..hash_name, {"plain", "scram_"..(hashprep(hash_name))}, scram_gen(hash_name:lower(), hash, hmac_hash));

		-- register channel binding equivalent

	end

	registerSCRAMMechanism("SHA-1", sha1, hmac_sha1);

end

return _M;