[ViewVC] Diff of: cvs/gvpe/doc/gvpe.texi

Comparing gvpe/doc/gvpe.texi (file contents):
Revision 1.5 by root, Tue Feb 15 13:31:22 2011 UTC vs.
Revision 1.6 by root, Wed Jun 18 20:40:52 2014 UTC

…		…
195		195
196	@example	196	@example
197	./configure --enable-hmac-length=4 --enable-rand-length=0	197	./configure --enable-hmac-length=4 --enable-rand-length=0
198	@end example	198	@end example
199		199
200	Minimize the header overhead of VPN packets (the above will result in only 4 bytes of overhead over the raw ethernet frame). This is a insecure configuration because a HMAC length of 4 makes collision attacks based on the birthday paradox pretty easy.	200	Minimize the header overhead of VPN packets (the above will result in only 4 bytes of overhead over the raw ethernet frame). This is a insecure configuration because a HMAC length of 4 makes collision attacks almost trivial.
201	@refill	201	@refill
202		202
203		203
204	@subsection MINIMIZE CPU TIME REQUIRED	204	@subsection MINIMIZE CPU TIME REQUIRED
205		205
…		…
214		214
215	@subsection MAXIMIZE SECURITY	215	@subsection MAXIMIZE SECURITY
216		216
217		217
218	@example	218	@example
219	./configure --enable-hmac-length=16 --enable-rand-length=8 --enable-digest=sha1	219	./configure --enable-hmac-length=16 --enable-rand-length=12 --enable-digest=ripemd610
220	@end example	220	@end example
221		221
222	This uses a 16 byte HMAC checksum to authenticate packets (I guess 8-12 would also be pretty secure ;) and will additionally prefix each packet with 8 bytes of random data. In the long run, people should move to SHA-256 and beyond).	222	This uses a 16 byte HMAC checksum to authenticate packets (I guess 8-12 would also be pretty secure ;) and will additionally prefix each packet with 12 bytes of random data.
223	@refill	223	@refill
224	In general, remember that AES-128 seems to be as secure but faster than AES-192 or AES-256, more randomness helps against sniffing and a longer HMAC helps against spoofing. MD4 is a fast digest, SHA1, RIPEMD160, SHA256 are consecutively better, and Blowfish is a fast cipher (and also quite secure).	224	In general, remember that AES-128 seems to be as secure but faster than AES-192 or AES-256, more randomness helps against sniffing and a longer HMAC helps against spoofing. MD4 is a fast digest, SHA1, RIPEMD160, SHA256 are consecutively better, and Blowfish is a fast cipher (and also quite secure).
225	@refill	225	@refill
226		226
227		227
…		…
606		606
607		607
608	@section DESCRIPTION	608	@section DESCRIPTION
609	The gvpe config file consists of a series of lines that contain @t{variable = value} pairs. Empty lines are ignored. Comments start with a @t{#} and extend to the end of the line. They can be used on their own lines, or after any directives. Whitespace is allowed around the @t{=} sign or after values, but not within the variable names or values themselves.	609	The gvpe config file consists of a series of lines that contain @t{variable = value} pairs. Empty lines are ignored. Comments start with a @t{#} and extend to the end of the line. They can be used on their own lines, or after any directives. Whitespace is allowed around the @t{=} sign or after values, but not within the variable names or values themselves.
610	@refill	610	@refill
611	The only exception to the above is the "on" directive that can prefix any @t{name = value} setting and will only "execute" it on the named node, or (if the nodename starts with "!") on all nodes except the named one.	611	All settings are applied "in order", that is, later settings of the same variable overwrite earlier ones.
612	@refill	612	@refill
		613	The only exceptions to the above are the following directives:
		614	@refill
		615
		616
		617	@itemize
		618
		619
		620	@item
		621	node nodename
		622
		623	Introduces a node section. The nodename is used to select the right configuration section and is the same string as is passed as an argument to the gvpe daemon.
		624	@refill
		625	Multiple @t{node} statements with the same node name are supported and will be merged together.
		626	@refill
		627
		628
		629	@item
		630	global
		631
		632	This statement switches back to the global section, which is mainly useful if you want to include a second config file, e..g for local customisations. To do that, simply include this at the very end of your config file:
		633	@refill
		634
		635
		636	@example
		637	global
		638	include local.conf
		639	@end example
		640
		641
		642
		643	@item
		644	on nodename ...
		645
		646
		647
		648	@item
		649	on !nodename ...
		650
		651	You can prefix any configuration directive with @t{on} and a nodename. GVPE will will only "execute" it on the named node, or (if the nodename starts with @t{!}) on all nodes except the named one.
		652	@refill
613	For example, set the MTU to @t{1450} everywhere, loglevel to @t{noise} on branch1, and connect to @t{ondemand} everywhere but on branch2:	653	Example: set the MTU to @t{1450} everywhere, @t{loglevel} to @t{noise} on @t{branch1}, and @t{connect} to @t{ondemand} everywhere but on branch2.
614	@refill	654	@refill
615		655
616		656
617	@example	657	@example
618	mtu = 1450	658	mtu = 1450
619	on branch1 loglevel = noise	659	on branch1 loglevel = noise
620	on !branch2 connect = ondemand	660	on !branch2 connect = ondemand
621	@end example	661	@end example
622		662
623	All settings are applied "in order", that is, later settings of the same variable overwrite earlier ones.	663
		664
		665	@item
		666	include relative-or-absolute-path
		667
		668	Reads the specified file (the path must not contain whitespace or @t{=} characters) and evaluate all config directives in it as if they were spelled out in place of the @t{include} directive.
624	@refill	669	@refill
		670	The path is a printf format string, that is, you must escape any @t{%} by doubling it, and you can have a single @t{%s} inside, which will be replaced by the current nodename.
		671	@refill
		672	Relative paths are interpreted relative to the GVPE config directory.
		673	@refill
		674	Example: include the file @file{local.conf} in the config directory on every node.
		675	@refill
		676
		677
		678	@example
		679	include local.conf
		680	@end example
		681
		682	Example: include a file @file{conf/}nodename@file{.conf}
		683	@refill
		684
		685
		686	@example
		687	include conf/%s.conf
		688	@end example
		689
		690	@end itemize
		691
625		692
626		693
627	@section ANATOMY OF A CONFIG FILE	694	@section ANATOMY OF A CONFIG FILE
628	Usually, a config file starts with a few global settings (like the UDP port to listen on), followed by node-specific sections that begin with a @t{node = nickname} line.	695	Usually, a config file starts with a few global settings (like the UDP port to listen on), followed by node-specific sections that begin with a @t{node = nickname} line.
629	@refill	696	@refill
…		…
643		710
644	@itemize	711	@itemize
645		712
646		713
647	@item	714	@item
		715	chroot = path or /
		716
		717	@cindex chroot
		718	Tells GVPE to chroot(2) to the specified path after reading all necessary files, binding to sockets and running the @t{if-up} script, but before running @t{node-up} or any other scripts.
		719	@refill
		720	The special path @file{/} instructs GVPE to create (and remove) an empty temporary directory to use as new root. This is most secure, but makes it impossible to use any scripts other than the @t{if-up} one.
		721	@refill
		722
		723
		724	@item
		725	chuid = numerical-uid
		726
		727	@cindex chuid
		728
		729
		730	@item
		731	chgid = numerical-gid
		732
		733	@cindex chgid
		734	These two options tell GVPE to change to the given user and/or group id after reading all necessary files, binding to sockets and running the @t{if-up} script.
		735	@refill
		736	Other scripts, such as @t{node-up}, are run with the new user id or group id.
		737	@refill
		738
		739
		740	@item
		741	chuser = username
		742
		743	@cindex chuser
		744	Alternative to @t{chuid} and @t{chgid}: Sets both @t{chuid} and @t{chgid} to the user and (primary) group ids of the specified user (for example, @t{nobody}).
		745	@refill
		746
		747
		748	@item
648	dns-forw-host = hostname/ip	749	dns-forw-host = hostname/ip
649		750
650	@cindex dns-forw-host	751	@cindex dns-forw-host
651	The DNS server to forward DNS requests to for the DNS tunnel protocol (default: @t{127.0.0.1}, changing it is highly recommended).	752	The DNS server to forward DNS requests to for the DNS tunnel protocol (default: @t{127.0.0.1}, changing it is highly recommended).
652	@refill	753	@refill
…		…
655	@item	756	@item
656	dns-forw-port = port-number	757	dns-forw-port = port-number
657		758
658	@cindex dns-forw-port	759	@cindex dns-forw-port
659	The port where the @t{dns-forw-host} is to be contacted (default: @t{53}, which is fine in most cases).	760	The port where the @t{dns-forw-host} is to be contacted (default: @t{53}, which is fine in most cases).
		761	@refill
		762
		763
		764	@item
		765	dns-case-preserving = yes\|true\|on \| no\|false\|off
		766
		767	@cindex dns-case-preserving
		768	Sets whether the DNS transport forwarding server preserves case (DNS servers have to, but some access systems are even more broken than others) (default: true).
		769	@refill
		770	Normally, when the forwarding server changes the case of domain names then GVPE will automatically set this to false.
660	@refill	771	@refill
661		772
662		773
663	@item	774	@item
664	dns-max-outstanding = integer-number-of-requests	775	dns-max-outstanding = integer-number-of-requests
…		…
894		1005
895	@item	1006	@item
896	keepalive = seconds	1007	keepalive = seconds
897		1008
898	@cindex keepalive	1009	@cindex keepalive
899	Sets the keepalive probe interval in seconds (default: @t{60}). After this many seconds of inactivity the daemon will start to send keepalive probe every 3 seconds until it receives a reply from the other end. If no reply is received within 15 seconds, the peer is considered unreachable and the connection is closed.	1010	Sets the keepalive probe interval in seconds (default: @t{60}). After this many seconds of inactivity the daemon will start to send keepalive probe every 3 seconds until it receives a reply from the other end. If no reply is received within 15 seconds, the peer is considered unreachable and the connection is closed.
900	@refill	1011	@refill
901		1012
902		1013
903	@item	1014	@item
904	loglevel = noise\|trace\|debug\|info\|notice\|warn\|error\|critical	1015	loglevel = noise\|trace\|debug\|info\|notice\|warn\|error\|critical
…		…
919	This value must be the minimum of the MTU values of all nodes.	1030	This value must be the minimum of the MTU values of all nodes.
920	@refill	1031	@refill
921		1032
922		1033
923	@item	1034	@item
924	node = nickname	1035	nfmark = integer
925		1036
926	@cindex node	1037	@cindex nfmark
927	Not really a config setting but introduces a node section. The nickname is used to select the right configuration section and must be passed as an argument to the gvpe daemon.	1038	This advanced option, when set to a nonzero value (default: @t{0}), tries to set the netfilter mark (or fwmark) value on all sockets gvpe uses to send packets.
928	@refill	1039	@refill
		1040	This can be used to make gvpe use a different set of routing rules. For example, on GNU/Linux, the @t{if-up} could set @t{nfmark} to 1000 and then put all routing rules into table @t{99} and then use an ip rule to make gvpe traffic avoid that routing table, in effect routing normal traffic via gvpe and gvpe traffic via the normal system routing tables:
		1041	@refill
		1042
		1043
		1044	@example
		1045	ip rule add not fwmark 1000 lookup 99
		1046	@end example
		1047
929		1048
930		1049
931	@item	1050	@item
932	node-up = relative-or-absolute-path	1051	node-up = relative-or-absolute-path
933		1052
…		…
996	@example	1115	@example
997	#!/bin/sh	1116	#!/bin/sh
998	@{	1117	@{
999	echo update delete $DESTNODE.lowttl.example.net. a	1118	echo update delete $DESTNODE.lowttl.example.net. a
1000	echo update add $DESTNODE.lowttl.example.net. 1 in a $DESTIP	1119	echo update add $DESTNODE.lowttl.example.net. 1 in a $DESTIP
1001	echo	1120	echo
1002	@} \| nsupdate -d -k $CONFBASE:key.example.net.	1121	@} \| nsupdate -d -k $CONFBASE:key.example.net.
1003	@end example	1122	@end example
1004		1123
1005		1124
1006		1125
…		…
1022		1141
1023	@item	1142	@item
1024	pid-file = path	1143	pid-file = path
1025		1144
1026	@cindex pid-file	1145	@cindex pid-file
1027	The path to the pid file to check and create (default: @t{LOCALSTATEDIR/run/gvpe.pid}).	1146	The path to the pid file to check and create (default: @t{LOCALSTATEDIR/run/gvpe.pid}). The first @t{%s} is replaced by the nodename - any other use of @t{%} must be written as @t{%%}.
1028	@refill	1147	@refill
1029		1148
1030		1149
1031	@item	1150	@item
1032	private-key = relative-path-to-key	1151	private-key = relative-path-to-key
…		…
1040		1159
1041	@item	1160	@item
1042	rekey = seconds	1161	rekey = seconds
1043		1162
1044	@cindex rekey	1163	@cindex rekey
1045	Sets the rekeying interval in seconds (default: @t{3600}). Connections are reestablished every @t{rekey} seconds, making them use a new encryption key.	1164	Sets the rekeying interval in seconds (default: @t{3607}). Connections are reestablished every @t{rekey} seconds, making them use a new encryption key.
1046	@refill	1165	@refill
1047		1166
1048		1167
1049	@item	1168	@item
1050	nfmark = integer	1169	seed-device = path
1051		1170
1052	@cindex nfmark	1171	@cindex seed-device
1053	This advanced option, when set to a nonzero value (default: @t{0}), tries to set the netfilter mark (or fwmark) value on all sockets gvpe uses to send packets.	1172	The random device used to initially and regularly seed the random number generator (default: @file{/dev/urandom}). Randomness is of paramount importance to the security of the algorithms used in gvpe.
1054	@refill	1173	@refill
1055	This can be used to make gvpe use a different set of routing rules. For example, on GNU/Linux, the @t{if-up} could set @t{nfmark} to 1000 and then put all routing rules into table @t{99} and then use an ip rule to make gvpe traffic avoid that routing table, in effect routing normal traffic via gvpe and gvpe traffic via the normal system routing tables:	1174	On program start and every seed-interval, gvpe will read 64 octets.
1056	@refill	1175	@refill
		1176	Setting this path to the empty string will disable this functionality completely (the underlying crypto library will likely look for entropy sources on it's own though, so not all is lost).
		1177	@refill
1057		1178
1058		1179
1059	@example	1180	@item
1060	ip rule add not fwmark 1000 lookup 99	1181	seed-interval = seconds
1061	@end example
1062		1182
		1183	@cindex seed-interval
		1184	The number of seconds between reseeds of the random number generator (default: @t{3613}). A value of @t{0} disables this regular reseeding.
		1185	@refill
		1186
		1187
		1188	@item
		1189	serial = string
		1190
		1191	@cindex serial
		1192	The configuration serial number. This can be any string up to 16 bytes length. Only when the serial matches on both sides of a conenction will the connection succeed. This is @emph{not} a security mechanism and eay to spoof, this mechanism exists to alert users that their config is outdated.
		1193	@refill
		1194	It's recommended to specify this is a date string such as @t{2013-05-05} or @t{20121205084417).}
		1195	@refill
		1196	The exact algorithm is as this: if a connection request is received form a node with an identical serial, then it succeeds normally.
		1197	@refill
		1198	If the remote serial is lower than the local serial, it is ignored.
		1199	@refill
		1200	If the remote serial is higher than the local serial, a warning message is logged.
		1201	@refill
1063	@end itemize	1202	@end itemize
1064		1203
1065		1204
1066		1205
1067	@subsection NODE SPECIFIC SETTINGS	1206	@subsection NODE SPECIFIC SETTINGS
…		…
1206	enable-udp = yes\|true\|on \| no\|false\|off	1345	enable-udp = yes\|true\|on \| no\|false\|off
1207		1346
1208	@cindex enable-udp	1347	@cindex enable-udp
1209	See gvpe.protocol(7) for a description of the UDP transport protocol.	1348	See gvpe.protocol(7) for a description of the UDP transport protocol.
1210	@refill	1349	@refill
1211	Enable the UDPv4 transport using the @t{udp-port} port (default: @t{no}, unless no other protocol is enabled for a node, in which case this protocol is enabled automatically).	1350	Enable the UDPv4 transport using the @t{udp-port} port (default: @t{no}).
1212	@refill
1213	NOTE: Please specify @t{enable-udp = yes} if you want to use it even though it might get switched on automatically, as some future version might default to another default protocol.
1214	@refill	1351	@refill
1215		1352
1216		1353
1217	@item	1354	@item
1218	hostname = hostname \| ip [can not be defaulted]	1355	hostname = hostname \| ip [can not be defaulted]
…		…
1249	Whether to inherit the TOS settings of packets sent to the tunnel when sending packets to this node (default: @t{yes}). If set to @t{yes} then outgoing tunnel packets will have the same TOS setting as the packets sent to the tunnel device, which is usually what you want.	1386	Whether to inherit the TOS settings of packets sent to the tunnel when sending packets to this node (default: @t{yes}). If set to @t{yes} then outgoing tunnel packets will have the same TOS setting as the packets sent to the tunnel device, which is usually what you want.
1250	@refill	1387	@refill
1251		1388
1252		1389
1253	@item	1390	@item
		1391	low-power = yes\|true\|on \| no\|false\|off
		1392
		1393	@cindex low-power
		1394	If true, designates a node as a low-power node. Low-power nodes use larger timeouts and try to reduce cpu time. Other nodes talking to a low-power node will also use larger timeouts, and will use less aggressive optimisations, in the hope of reducing load. Security is not compromised.
		1395	@refill
		1396	The typical low-power node would be a mobile phone, where wakeups and encryption can significantly increase power drain.
		1397	@refill
		1398
		1399
		1400	@item
1254	max-retry = positive-number	1401	max-retry = positive-number
1255		1402
1256	@cindex max-retry	1403	@cindex max-retry
1257	The maximum interval in seconds (default: @t{3600}, one hour) between retries to establish a connection to this node. When a connection cannot be established, gvpe uses exponential back-off capped at this value. It's sometimes useful to set this to a much lower value (e.g. @t{120}) on connections to routers that usually are stable but sometimes are down, to assure quick reconnections even after longer downtimes.	1404	The maximum interval in seconds (default: @t{3600}, one hour) between retries to establish a connection to this node. When a connection cannot be established, gvpe uses exponential back-off capped at this value. It's sometimes useful to set this to a much lower value (e.g. @t{120}) on connections to routers that usually are stable but sometimes are down, to assure quick reconnections even after longer downtimes.
1258	@refill	1405	@refill
…		…
1340		1487
1341		1488
1342	@item	1489	@item
1343	hostkey	1490	hostkey
1344		1491
1345	The private key (taken from @t{hostkeys/nodename}) of the current host.	1492	The (default path of the) private key of the current host.
1346	@refill	1493	@refill
1347		1494
1348		1495
1349	@item	1496	@item
1350	pubkey/nodename	1497	pubkey/nodename
…		…
1626		1773
1627		1774
1628	@section Overview	1775	@section Overview
1629	GVPE can make use of a number of protocols. One of them is the GNU VPE protocol which is used to authenticate tunnels and send encrypted data packets. This protocol is described in more detail the second part of this document.	1776	GVPE can make use of a number of protocols. One of them is the GNU VPE protocol which is used to authenticate tunnels and send encrypted data packets. This protocol is described in more detail the second part of this document.
1630	@refill	1777	@refill
1631	The first part of this document describes the transport protocols which are used by GVPE to send it's data packets over the network.	1778	The first part of this document describes the transport protocols which are used by GVPE to send its data packets over the network.
1632	@refill	1779	@refill
1633		1780
1634		1781
1635	@section PART 1: Transport protocols	1782	@section PART 1: Transport protocols
1636	GVPE offers a wide range of transport protocols that can be used to interchange data between nodes. Protocols differ in their overhead, speed, reliability, and robustness.	1783	GVPE offers a wide range of transport protocols that can be used to interchange data between nodes. Protocols differ in their overhead, speed, reliability, and robustness.
…		…
1663	It should be used if RAW IP is not available.	1810	It should be used if RAW IP is not available.
1664	@refill	1811	@refill
1665		1812
1666		1813
1667	@subsection TCP	1814	@subsection TCP
1668	This protocol is a very bad choice, as it not only has high overhead (more than 60 bytes), but the transport also retries on it's own, which leads to congestion when the link has moderate packet loss (as both the TCP transport and the tunneled traffic will retry, increasing congestion more and more). It also has high latency and is quite inefficient.	1815	This protocol is a very bad choice, as it not only has high overhead (more than 60 bytes), but the transport also retries on its own, which leads to congestion when the link has moderate packet loss (as both the TCP transport and the tunneled traffic will retry, increasing congestion more and more). It also has high latency and is quite inefficient.
1669	@refill	1816	@refill
1670	It's only useful when tunneling through firewalls that block better protocols. If a node doesn't have direct internet access but a HTTP proxy that supports the CONNECT method it can be used to tunnel through a web proxy. For this to work, the @t{tcp-port} should be @t{443} (@t{https}), as most proxies do not allow connections to other ports.	1817	It's only useful when tunneling through firewalls that block better protocols. If a node doesn't have direct internet access but a HTTP proxy that supports the CONNECT method it can be used to tunnel through a web proxy. For this to work, the @t{tcp-port} should be @t{443} (@t{https}), as most proxies do not allow connections to other ports.
1671	@refill	1818	@refill
1672	It is an abuse of the usage a proxy was designed for, so make sure you are allowed to use it for GVPE.	1819	It is an abuse of the usage a proxy was designed for, so make sure you are allowed to use it for GVPE.
1673	@refill	1820	@refill
…		…
1680	@refill	1827	@refill
1681	This is the worst choice of transport protocol with respect to overhead (overhead can be 2-3 times higher than the transferred data), and latency (which can be many seconds). Some DNS servers might not be prepared to handle the traffic and drop or corrupt packets. The client also has to constantly poll the server for data, so the client will constantly create traffic even if it doesn't need to transport packets.	1828	This is the worst choice of transport protocol with respect to overhead (overhead can be 2-3 times higher than the transferred data), and latency (which can be many seconds). Some DNS servers might not be prepared to handle the traffic and drop or corrupt packets. The client also has to constantly poll the server for data, so the client will constantly create traffic even if it doesn't need to transport packets.
1682	@refill	1829	@refill
1683	In addition, the same problems as the TCP transport also plague this protocol.	1830	In addition, the same problems as the TCP transport also plague this protocol.
1684	@refill	1831	@refill
1685	It's only use is to tunnel through firewalls that do not allow direct internet access. Similar to using a HTTP proxy (as the TCP transport does), it uses a local DNS server/forwarder (given by the @t{dns-forw-host} configuration value) as a proxy to send and receive data as a client, and an @t{NS} record pointing to the GVPE server (as given by the @t{dns-hostname} directive).	1832	Its only use is to tunnel through firewalls that do not allow direct internet access. Similar to using a HTTP proxy (as the TCP transport does), it uses a local DNS server/forwarder (given by the @t{dns-forw-host} configuration value) as a proxy to send and receive data as a client, and an @t{NS} record pointing to the GVPE server (as given by the @t{dns-hostname} directive).
1686	@refill	1833	@refill
1687	The only good side of this protocol is that it can tunnel through most firewalls mostly undetected, iff the local DNS server/forwarder is sane (which is true for most routers, wireless LAN gateways and nameservers).	1834	The only good side of this protocol is that it can tunnel through most firewalls mostly undetected, iff the local DNS server/forwarder is sane (which is true for most routers, wireless LAN gateways and nameservers).
1688	@refill	1835	@refill
1689	Fine-tuning needs to be done by editing @t{src/vpn_dns.C} directly.	1836	Fine-tuning needs to be done by editing @t{src/vpn_dns.C} directly.
1690	@refill	1837	@refill
…		…
1704	+------+------+--------+------+	1851	+------+------+--------+------+
1705	\| HMAC \| TYPE \| SRCDST \| DATA \|	1852	\| HMAC \| TYPE \| SRCDST \| DATA \|
1706	+------+------+--------+------+	1853	+------+------+--------+------+
1707	@end example	1854	@end example
1708		1855
1709	The HMAC field is present in all packets, even if not used (e.g. in auth request packets), in which case it is set to all zeroes. The checksum itself is calculated over the TYPE, SRCDST and DATA fields in all cases.	1856	The HMAC field is present in all packets, even if not used (e.g. in auth request packets), in which case it is set to all zeroes. The MAC itself is calculated over the TYPE, SRCDST and DATA fields in all cases.
1710	@refill	1857	@refill
1711	The TYPE field is a single byte and determines the purpose of the packet (e.g. RESET, COMPRESSED/UNCOMPRESSED DATA, PING, AUTH REQUEST/RESPONSE, CONNECT REQUEST/INFO etc.).	1858	The TYPE field is a single byte and determines the purpose of the packet (e.g. RESET, COMPRESSED/UNCOMPRESSED DATA, PING, AUTH REQUEST/RESPONSE, CONNECT REQUEST/INFO etc.).
1712	@refill	1859	@refill
1713	SRCDST is a three byte field which contains the source and destination node IDs (12 bits each).	1860	SRCDST is a three byte field which contains the source and destination node IDs (12 bits each).
1714	@refill	1861	@refill
…		…
1722	+------+------+--------+------+-------+------+	1869	+------+------+--------+------+-------+------+
1723	@end example	1870	@end example
1724		1871
1725	RAND is a sequence of fully random bytes, used to increase the entropy of the data for encryption purposes.	1872	RAND is a sequence of fully random bytes, used to increase the entropy of the data for encryption purposes.
1726	@refill	1873	@refill
1727	SEQNO is a 32-bit sequence number. It is negotiated at every connection initialization and starts at some random 31 bit value. VPE currently uses a sliding window of 512 packets/sequence numbers to detect reordering, duplication and replay attacks.	1874	SEQNO is a 32-bit sequence number. It is negotiated at every connection initialization and starts at some random 31 bit value. GVPE currently uses a sliding window of 512 packets/sequence numbers to detect reordering, duplication and replay attacks.
1728	@refill	1875	@refill
		1876	The encryption is done on RAND+SEQNO+DATA in CBC mode with zero IV (or, equivalently, the IV is RAND+SEQNO, encrypted with the block cipher, unless RAND size is decreased or increased over the default value).
		1877	@refill
		1878	The random prefix itself is generated by using AES in CTR mode with a random key and starting value, which should make them unpredictable even before encrypting them again. The sequence number additionally ensures that the IV is unique.
		1879	@refill
1729		1880
1730		1881
1731	@subsection The authentication protocol	1882	@subsection The authentication/key exchange protocol
1732	Before nodes can exchange packets, they need to establish authenticity of the other side and a key. Every node has a private RSA key and the public RSA keys of all other nodes.	1883	Before nodes can exchange packets, they need to establish authenticity of the other side and a key. Every node has a private RSA key and the public RSA keys of all other nodes.
1733	@refill	1884	@refill
1734	A host establishes a simplex connection by sending the other node an RSA encrypted challenge containing a random challenge (consisting of the encryption key to use when sending packets, more random data and PKCS1_OAEP padding) and a random 16 byte "challenge-id" (used to detect duplicate auth packets). The destination node will respond by replying with an (unencrypted) RIPEMD160 hash of the decrypted challenge, which will authenticate that node. The destination node will also set the outgoing encryption parameters as given in the packet.	1885	When a node wants to establish a connection to another node, it sends an RSA-OEAP-encrypted challenge and an ECDH (curve25519) key. The other node replies with its own ECDH key and a HKDF of the challenge and both ECDH keys to prove its identity.
1735	@refill	1886	@refill
1736	When the source node receives a correct auth reply (by verifying the hash and the id, which will expire after 120 seconds), it will start to accept data packets from the destination node.	1887	The remote node enganges in exactly the same protocol. When both nodes have exchanged their challenge and verified the response, they calculate a cipher key and a HMAC key and start exchanging data packets.
1737	@refill	1888	@refill
1738	This means that a node can only initiate a simplex connection, telling the other side the key it has to use when it sends packets. The challenge reply is only used to set the current IP address of the other side and protocol parameters.	1889	In detail, the challenge consist of:
1739	@refill	1890	@refill
1740	This protocol is completely symmetric, so to be able to send packets the destination node must send a challenge in the exact same way as already described (so, in essence, two simplex connections are created per node pair).	1891
		1892
		1893	@example
		1894	RSA-OAEP (SEQNO MAC CIPHER SALT EXTRA-AUTH) ECDH1
		1895	@end example
		1896
		1897	That is, it encrypts (with the public key of the remote node) an initial sequence number for data packets, key material for the HMAC key, key material for the cipher key, a salt used by the HKDF (as shown later) and some extra random bytes that are unused except for authentication. It also sends the public key of a curve25519 exchange.
		1898	@refill
		1899	The remote node decrypts the RSA data, generates its own ECDH key (ECDH2), and replies with:
		1900	@refill
		1901
		1902
		1903	@example
		1904	HKDF-Expand (HKDF-Extract (ECDH2, RSA), ECDH1, AUTH_DIGEST_SIZE) ECDH2
		1905	@end example
		1906
		1907	That is, it extracts from the decrypted RSA challenge, using its ECDH key as salt, and then expands using the requesting node's ECDH1 key. The resulting hash is returned as a proof that the node could decrypt the RSA challenge data, together with the ECDH key.
		1908	@refill
		1909	After both nodes have done this to each other, they calculate the shared ECDH secret, cipher and HMAC keys for the session (each node generates two cipher and HMAC keys, one for sending and one for receiving).
		1910	@refill
		1911	The HMAC key for sending is generated as follow:
		1912	@refill
		1913
		1914
		1915	@example
		1916	HMAC_KEY = HKDF-Expand (HKDF-Extract (REMOTE_SALT, MAC ECDH_SECRET), info, HMAC_MD_SIZE)
		1917	@end example
		1918
		1919	It extracts from MAC and ECDH_SECRET using the @emph{remote} SALT, then expands using a static info string.
		1920	@refill
		1921	The cipher key is generated in the same way, except using the CIPHER part of the original challenge.
		1922	@refill
		1923	The result of this process is to authenticate each node to the other node, while exchanging keys using both RSA and ECDH, the latter providing perfect forward secrecy.
		1924	@refill
		1925	The protocol has been overdesigned where this was possible without increasing implementation complexity, in an attempt to protect against implementation or protocol failures. For example, if the ECDH challenge was found to be flawed, perfect forward secrecy would be lost, but the data would likely still be protected. Likewise, standard algorithms and implementations are used where possible.
1741	@refill	1926	@refill
1742		1927
1743		1928
1744	@subsection Retrying	1929	@subsection Retrying
1745	When there is no response to an auth request, the node will send auth requests in bursts with an exponential back-off. After some time it will resort to PING packets, which are very small (8 bytes + protocol header) and lightweight (no RSA operations required). A node that receives ping requests from an unconnected peer will respond by trying to create a connection.	1930	When there is no response to an auth request, the node will send auth requests in bursts with an exponential back-off. After some time it will resort to PING packets, which are very small (8 bytes + protocol header) and lightweight (no RSA operations required). A node that receives ping requests from an unconnected peer will respond by trying to create a connection.
…		…
1751	Sending packets over the VPN will reset the retry intervals as well, which means as long as somebody is trying to send packets to a given node, GVPE will try to connect every few seconds.	1936	Sending packets over the VPN will reset the retry intervals as well, which means as long as somebody is trying to send packets to a given node, GVPE will try to connect every few seconds.
1752	@refill	1937	@refill
1753		1938
1754		1939
1755	@subsection Routing and Protocol translation	1940	@subsection Routing and Protocol translation
1756	The GVPE routing algorithm is easy: there isn't much routing to speak of: When routing packets to another node, GVPE trues the following options, in order:	1941	The GVPE routing algorithm is easy: there isn't much routing to speak of: When routing packets to another node, GVPE tries the following options, in order:
1757	@refill	1942	@refill
1758		1943
1759		1944
1760	@itemize	1945	@itemize
1761		1946
…		…
1783	@item	1968	@item
1784	Failing all that, the packet will be dropped.	1969	Failing all that, the packet will be dropped.
1785		1970
1786	@end itemize	1971	@end itemize
1787		1972
1788	A host can usually declare itself unreachable directly by setting it's port number(s) to zero. It can declare other hosts as unreachable by using a config-file that disables all protocols for these other hosts. Another option is to disable all protocols on that host in the other config files.	1973	A host can usually declare itself unreachable directly by setting its port number(s) to zero. It can declare other hosts as unreachable by using a config-file that disables all protocols for these other hosts. Another option is to disable all protocols on that host in the other config files.
1789	@refill	1974	@refill
1790	If two hosts cannot connect to each other because their IP address(es) are not known (such as dial-up hosts), one side will send a @emph{mediated} connection request to a router (routers must be configured to act as routers!), which will send both the originating and the destination host a connection info request with protocol information and IP address of the other host (if known). Both hosts will then try to establish a direct connection to the other peer, which is usually possible even when both hosts are behind a NAT gateway.	1975	If two hosts cannot connect to each other because their IP address(es) are not known (such as dial-up hosts), one side will send a @emph{mediated} connection request to a router (routers must be configured to act as routers!), which will send both the originating and the destination host a connection info request with protocol information and IP address of the other host (if known). Both hosts will then try to establish a direct connection to the other peer, which is usually possible even when both hosts are behind a NAT gateway.
1791	@refill	1976	@refill
1792	Routing via other nodes works because the SRCDST field is not encrypted, so the router can just forward the packet to the destination host. Since each host uses it's own private key, the router will not be able to decrypt or encrypt packets, it will just act as a simple router and protocol translator.	1977	Routing via other nodes works because the SRCDST field is not encrypted, so the router can just forward the packet to the destination host. Since each host uses its own private key, the router will not be able to decrypt or encrypt packets, it will just act as a simple router and protocol translator.
1793	@refill	1978	@refill
1794		1979
1795		1980
1796		1981
1797	@node Simple Example,Complex Example,gvpe.protocol,Top	1982	@node Simple Example,Complex Example,gvpe.protocol,Top

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Revision 1.6 by root, Wed Jun 18 20:40:52 2014 UTC