Adding erlang spa server component

erlang/README.md

@@ -13,10 +13,13 @@ Usage
 -----
   
     $ rebar3 shell
-    1> fwknop:knock("spaserver.domain.com", 62201, "Sz80RjpXOlhH2olGuKBUamHKcqyMBsS9BTgLaMugUsg=", "c0TOaMJ2aVPdYTh4Aa25Dwxni7PrLo2zLAtBoVwSepkvH6nLcW45Cjb9zaEC2SQd03kaaV+Ckx3FhCh5ohNM5Q==", { tcp, "1.1.1.1", 22 } ).
+    1> server:start("Sz80RjpXOlhH2olGuKBUamHKcqyMBsS9BTgLaMugUsg=", "c0TOaMJ2aVPdYTh4Aa25Dwxni7PrLo2zLAtBoVwSepkvH6nLcW45Cjb9zaEC2SQd03kaaV+Ckx3FhCh5ohNM5Q==").
+    2> fwknop:knock("spaserver.domain.com", 62201, "Sz80RjpXOlhH2olGuKBUamHKcqyMBsS9BTgLaMugUsg=", "c0TOaMJ2aVPdYTh4Aa25Dwxni7PrLo2zLAtBoVwSepkvH6nLcW45Cjb9zaEC2SQd03kaaV+Ckx3FhCh5ohNM5Q==", { tcp, "1.1.1.1", 22 } ).
     =INFO REPORT==== 15-Nov-2016::15:49:16 ===
     Message: 0428888364523312:bXMxNzg0:1479224956:2.0.2:1:MTI3LjAuMC4xLHRjcC84NDQz
     =INFO REPORT==== 15-Nov-2016::15:49:16 ===
     HMAC:   KDZrTwZ+gFpqgzk8+BCXvYhRCxCzk084UyNzhihiWLU
     ok
-    2>
+    Client request:{127,0,0,1}
+    Got message: <<"1.1.1.1,tcp/22">>
+    3>

erlang/src/server.erl

@@ -0,0 +1,102 @@
+%%  License (GNU General Public License):
+%%
+%%  This program is free software; you can redistribute it and/or
+%%  modify it under the terms of the GNU General Public License
+%%  as published by the Free Software Foundation; either version 2
+%%  of the License, or (at your option) any later version.
+%%
+%%  This program is distributed in the hope that it will be useful,
+%%  but WITHOUT ANY WARRANTY; without even the implied warranty of
+%%  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+%%  GNU General Public License for more details.
+%%
+%%  You should have received a copy of the GNU General Public License
+%%  along with this program; if not, write to the Free Software
+%%  Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307
+%%  USA
+
+-module( server ).
+-compile( export_all ).
+
+-import( fwknop, [ strip_base64/1, pbkdf1/2 ] ).
+-export( [ start/2 ] ).
+
+start(RijndaelKeyB64, HmacKeyB64) ->
+	spawn(fun() -> server(62201, RijndaelKeyB64, HmacKeyB64) end).
+
+server(Port, RijndaelKeyB64, HmacKeyB64) ->
+	{ok, Socket} = gen_udp:open(Port, [binary, {active, false}]),
+	accept(Socket, { RijndaelKeyB64, HmacKeyB64 } ).
+
+accept(Socket, { Key, Hmac } = Creds) ->
+	inet:setopts(Socket, [{active, once}]),
+	receive
+		{udp, Socket, Host, _, Bin} ->
+			io:format("Client request:~p~n",[Host]),
+			{ok, Ciphertext} 	= verify( Bin, Hmac ),
+			{ok, Plaintext} 	= decrypt( Ciphertext, Key ),
+			{ok, Message}		= decode( Plaintext ),
+			error_logger:info_msg( "Got message: ~p", [ Message ] ),
+
+			accept( Socket, Creds )
+	end.
+
+verify( SpaData, HmacKeyB64 ) ->
+	Magic		= <<"U2FsdGVkX1">>,
+	HmacKey		= base64:decode( HmacKeyB64 ),
+
+	% sha2.h:#define SHA256_B64_LEN          43
+	HmacLen 	= 43,
+
+	% write something to just split this on size vs two parts
+	DataHmac		= binary:part(SpaData, {byte_size(SpaData), -HmacLen}),
+	EncodedMsg		= binary:part(SpaData, {0, byte_size(SpaData) - HmacLen}),
+
+	ExpectedHmac		= fwknop:strip_base64( base64:encode( crypto:hmac( sha256, HmacKey, << Magic/binary, EncodedMsg/binary >> ) ) ),
+
+	%io:format("DataHmac: ~s~n",[DataHmac]),
+	%io:format("ExpectedHmac: ~s~n",[ExpectedHmac]),
+
+	ExpectedHmac 	= DataHmac,
+
+	% handle replay-attack (just compare hmacs or decode to digests?)
+	% verify len is a blocksize?
+
+	DecodedData		= base64:decode( unstrip_base64( <<Magic/binary, EncodedMsg/binary>> ) ),
+	% skip "Salted__"
+	DecodedMsg		= binary:part( DecodedData, {byte_size(DecodedData), -(byte_size(DecodedData) - 8) } ),
+	
+	{ ok, DecodedMsg }.
+
+decrypt( Ciphertext, RijndaelKeyB64 ) ->
+	RijndaelKey	= base64:decode( RijndaelKeyB64 ),
+
+	% split again on size
+	Salt 		= binary:part( Ciphertext, {0, 8} ),
+	EncryptedMsg	= binary:part( Ciphertext, {byte_size(Ciphertext), -(byte_size(Ciphertext) - 8) } ),
+
+	{Key, IV} 	= fwknop:pbkdf1( Salt, RijndaelKey ),
+
+	{ok, crypto:block_decrypt( aes_cbc256, Key, IV, EncryptedMsg ) }.
+	
+decode( Plaintext ) ->
+	Unpadded 		= pkcs7:unpad( Plaintext ),
+
+	%[Rand, User, Time, Version, MsgType, Request, Digest] = re:split( Unpadded, ":", [{return,binary}]),
+	%io:format( "~s:~s:~s:~s:~s:~s:~s~n", [ Rand, User, Time, Version, MsgType, Request, Digest] ),
+	[_, _, _, _, _, Request, _] = re:split( Unpadded, ":", [{return,binary}]),
+
+	[Ip, Proto, Port] = re:split( base64:decode( unstrip_base64( Request) ), "[,/]", [{return,binary}]),
+	Message = list_to_binary( io_lib:format( "~s,~s/~s", [ Ip, Proto, Port ]  ) ),
+
+	{ok, Message}.
+
+%
+%  miscellaneous utilities
+%
+unstrip_base64( Bin ) ->
+	case ( size( Bin ) rem 4 ) of
+		0 -> Bin;
+		N -> Pad = list_to_binary(string:copies("=", (4-N) )),
+			<< Bin/binary, Pad/binary >>
+	end.