-- 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 s_match = string.match;

local type = type

local string = string

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

local xor = require "bit".bxor

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");

module "scram"

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

--SASL SCRAM-SHA-1 according to draft-ietf-sasl-scram-10

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 function binaryXOR( a, b )

	end

end

-- hash algorithm independent Hi(PBKDF2) implementation

local 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 scram_sha_1(self, message)

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

	if not self.state.name then

		-- we are processing client_first_message

		local client_first_message = message;

		self.state["client_first_message"] = client_first_message;

		self.state["name"] = client_first_message:match("n=(.+),r=")

		self.state["clientnonce"] = client_first_message:match("r=([^,]+)")

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

			return "failure", "malformed-request";

		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();

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

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

		self.state["server_first_message"] = server_first_message;

		return "challenge", server_first_message

	else

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

		-- we are processing client_final_message

		local client_final_message = message;

		self.state["proof"] = client_final_message:match("p=(.+)");

		self.state["nonce"] = client_final_message:match("r=(.+),p=");

		self.state["channelbinding"] = client_final_message:match("c=(.+),r=");

		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

		local password, state;

		if self.profile.plain then

			password, state = self.profile.plain(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

		end

		local SaltedPassword = Hi(hmac_sha1, password, self.state.salt, default_i)

		local ClientKey = hmac_sha1(SaltedPassword, "Client Key")

		local ServerKey = hmac_sha1(SaltedPassword, "Server Key")

		local StoredKey = sha1(ClientKey)

		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_sha1(StoredKey, AuthMessage)

		local ClientProof     = binaryXOR(ClientKey, ClientSignature)

		local ServerSignature = hmac_sha1(ServerKey, AuthMessage)

		if base64.encode(ClientProof) == self.state.proof 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

function init(registerMechanism)

	registerMechanism("SCRAM-SHA-1", {"plain"}, scram_sha_1);

end

return _M;