secnet - flexible VPN software See LICENCE for legal information and CREDITS for a list of contributors. * Introduction secnet allows large virtual private networks to be constructed spanning multiple separate sites. It is designed for the case where a private network connecting many hosts is 'hidden' behind a single globally-routable IP address, but can also be applied in other circumstances. It communicates entirely using UDP, and works well with gateways that implement network address translation. If you are installing secnet to join an existing VPN, you should read the 'INSTALL' file and your particular VPN's documentation now. You may need to refer back to this file for information on the netlink and comm sections of the configuration file. If you are thinking about setting up a new VPN of any size (from one providing complete links between multiple sites to a simple laptop-to-host link), read the section in this file on 'Creating a VPN'. * Mailing lists and bug reporting There are two mailing lists associated with secnet: an 'announce' list and a 'discuss' list. Their addresses are: http://www.chiark.greenend.org.uk/mailman/listinfo/secnet-announce http://www.chiark.greenend.org.uk/mailman/listinfo/secnet-discuss The -announce list receives one message per secnet release. The -discuss list is for general discussion, including help with configuration, bug reports, feature requests, etc. Bug reports should be sent to <steve@greenend.org.uk>; they will be forwarded to the -discuss list by me. * Creating a VPN XXX TODO * secnet configuration file format By default secnet on linux reads /etc/secnet/secnet.conf. The default may be different on other platforms. This file defines a dictionary (a mapping from keys to values) full of configuration information for secnet. Two keys must be defined in this file for secnet to start. One is "system", a dictionary containing systemwide control parameters. The other is "sites", a list of all the sites that you intend to communicate with. The configuration file has a very simple syntax; keys are defined as follows: key definition; or key = definition; (the "=" is optional) Keys must match the following regular expression: [[:alpha:]_][[:alnum:]\-_]* i.e. the first character must be an alpha or an underscore, and the remaining characters may be alphanumeric, '-' or '_'. Keys can be defined to be a comma-separated list of any of the following types: a boolean a string, in quotes a number, in decimal a dictionary of definitions, enclosed in { } a "closure", followed by arguments a path to a key that already exists, to reference that definition Note that dictionaries can be nested: a key in one dictionary can refer to another dictionary. When secnet looks for a key in a particular directory and can't find it, it looks in the dictionary's lexical 'parents' in turn until it finds it (or fails to find it at all and stops with an error). Definitions can refer to previous definitions by naming them with a path. Paths are key1/key2/key3... (starting from wherever we find key1, i.e. in the current dictionary or any of its parents), or alternatively /key1/key2/key3... (to start from the root). Definitions cannot refer to future definitions. Example: a=1; b=2; c={ d=3; e=a; }; f={ a=4; g=c; }; The following paths are valid: a is 1 b is 2 c is a dictionary: c/d is 3 c/e is 1 f is a dictionary: f/a is 4 f/g is a dictionary: f/g/d is 3 f/g/e is 1 Note that f/g/e is NOT 4. Elements that are lists are inserted into lists in definitions, not referenced by them (i.e. you can't have lists of lists). Some closures may be followed by an argument list in ( ), and may return any number of whatever type they like (including other closures). Some types of closure (typically those returned from invokations of other closures) cannot be invoked. closure { definitions } is short for closure({definitions}). The main body of secnet, and all the additional modules, predefine some keys in the root dictionary. The main ones are: yes, true, True, TRUE, on: the boolean value True no, false, False, FALSE, off: the boolean value False makelist: turns a dictionary (arg1) into a list of definitions (ignoring the keys) readfile: reads a file (arg1) and returns it as a string map: applies the closure specified as arg1 to each of the remaining elements in the list in turn. Returns a list made up of the outputs of the closure. Keys defined by modules are described below, in the module documentation. Other configuration files can be included inline by writing "include filename" at the start of a line. After the configuration file is read, secnet looks for particular keys in configuration space to tell it what to do: system: a dictionary which can contain the following keys: log (log closure): a destination for system messages userid (string): the userid for secnet to run as once it drops privileges pidfile (string): where to store its PID sites: a list of closures of type 'site', which define other tunnel endpoints that secnet will attempt to communicate with * secnet command line options Usage: secnet [OPTION]... -f, --silent, --quiet suppress error messages -w, --nowarnings suppress warnings -v, --verbose output extra diagnostics -c, --config=filename specify a configuration file -j, --just-check-config stop after reading configfile -n, --nodetach do not run in background -d, --debug=item,... set debug options --help display this help and exit --version output version information and exit * base91s secnet defines a variant of the base91 encoding `basE91', from http://base91.sourceforge.net/ base91s is the same as baseE91 except that: - in the encoded charset, `"' is replaced with `-' - spaces, newlines etc. and other characters outside the charset are not permitted (although in some places they may be ignored, this is not guaranteed). * secnet builtin modules ** resolver Defines: adns (closure => resolver closure) adns: dict argument config (string): optional, a resolv.conf for ADNS to use ** random Defines: randomsrc (closure => randomsrc closure) randomsrc: string[,bool] arg1: filename of random source arg2: if True then source is blocking ** udp Defines: udp (closure => comm closure) udp: dict argument address (string list): IPv6 or IPv4 addresses to listen and send on; default is all local addresses port (integer): UDP port to listen and send on; optional if you don't need to have a stable address for your peers to talk to (in which case your site ought probably to have `local-mobile true'). buffer (buffer closure): buffer for incoming packets authbind (string): optional, path to authbind-helper program ** polypath Defines: polypath (closure => comm closure) polypath: dict argument port (integer): UDP port to listen and send on buffer (buffer closure): buffer for incoming packets authbind (string): optional, path to authbind-helper program max-interfaces (number): optional, max number of different interfaces to use (also, maximum steady-state amount of packet multiplication); interfaces marked with `@' do not count. interfaces (string list): which interfaces to process; each entry is optionally `!' or `+' or `@' followed by a glob pattern (which is applied to a prospective interface using fnmatch with no flags). `+' or nothing means to process normally. `!' means to ignore; `@' means to use only in conjunction with dedicated-interface-addr. If no list is specified, or the list ends with a `!' entry, a default list is used/appended: "!tun*","!tap*","!sl*","!userv*","!lo","@hippo*","*". Patterns which do not start with `*' or an alphanumeric need to be preceded by `!' or `+' or `@'. monitor-command (string list): Program to use to monitor appearance and disappearance of addresses on local network interfaces. Should produce lines of the form `+|-<ifname> 4|6 <addr>' where <addr> is an address literal. Each - line should relate to a previously printed + line. On startup, should produce a + line for each currently existing address. secnet does filtering so there is no need to strip out tun interfaces, multicast addresses, and so on. The command is run as the user secnet is started as (not the one which secnet may drop privilege to due to the configured `userid'). The default depends on the operating system. permit-loopback (boolean): Normally, loopback IPv6 and IPv4 addresses on local interfaces are disregarded, because such interfaces are not interesting for communicating with distant hosts. Setting this option will ignore that check, which can be useful for testing. Setting this option also removes "!lo*" from the default interface pattern list. When using this comm, packets are sent out of every active interface on the host (where possible). It is important that interfaces created by secnet itself are not included! secnet's default filter list tries to do this. This comm only makes sense for sites which are mobile. That is, the site closures used with this comm should all have the `local-mobile' parameter set to `true'. When the local site site is not marked mobile the address selection machinery might fixate on an unsuitable address. polypath takes site-specific informtion as passed to the `comm-info' site closure parameter. The entries understood in the dictionary are: dedicated-interface-addr (string): IPv4 or IPv6 address literal. Interfaces specified with `@' in `interfaces' will be used for the corresponding site iff the interface local address is this address. For an interface to work with polypath, it must either have a suitable default route, or be a point-to-point interface. In the general case this might mean that the host would have to have multiple default routes. However in practice the most useful configuration is two interfaces being (1) wifi (2) mobile internet. I have had success on Linux by using network-manager for wifi and invoking ppp directly for mobile internet. ppp sets up a point-to-point link, and does not add a default route if there already is one. network-manager always sets up a default route. The result is that the wifi always has a default route (so is useable); ppp (being a point-to-point link) does not need one. The use of polypath requires that secnet be started with root privilege, to make the setsockopt(,,SO_BINDTODEVICE,) calls. If the configuration specifies that secnet should drop privilege (see `userid' above), secnet will keep a special process around for this purpose; that process will handle local network interface changes but does not deal with any packets, key exchange, etc. polypath support is only available when secnet is built against an IPv6-capable version of adns (because it wants features in the newer adns). ** log Defines: logfile (closure => log closure) syslog (closure => log closure) logfile: dict argument filename (string): where to log to; default is stderr prefix (string): added to messages [""] class (string list): what type of messages to log { "debug-config", M_DEBUG_CONFIG }, { "debug-phase", M_DEBUG_PHASE }, { "debug", M_DEBUG }, { "all-debug", M_DEBUG|M_DEBUG_PHASE|M_DEBUG_CONFIG }, { "info", M_INFO }, { "notice", M_NOTICE }, { "warning", M_WARNING }, { "error", M_ERROR }, { "security", M_SECURITY }, { "fatal", M_FATAL }, { "default", M_WARNING|M_ERROR|M_SECURITY|M_FATAL }, { "verbose", M_INFO|M_NOTICE|M_WARNING|M_ERROR|M_SECURITY|M_FATAL }, { "quiet", M_FATAL } logfile will close and reopen its file upon receipt of SIGHUP. syslog: dict argument ident (string): include this string in every log message facility (string): facility to log as { "authpriv", LOG_AUTHPRIV }, { "cron", LOG_CRON }, { "daemon", LOG_DAEMON }, { "kern", LOG_KERN }, { "local0", LOG_LOCAL0 }, { "local1", LOG_LOCAL1 }, { "local2", LOG_LOCAL2 }, { "local3", LOG_LOCAL3 }, { "local4", LOG_LOCAL4 }, { "local5", LOG_LOCAL5 }, { "local6", LOG_LOCAL6 }, { "local7", LOG_LOCAL7 }, { "lpr", LOG_LPR }, { "mail", LOG_MAIL }, { "news", LOG_NEWS }, { "syslog", LOG_SYSLOG }, { "user", LOG_USER }, { "uucp", LOG_UUCP } ** util Defines: sysbuffer (closure => buffer closure) sysbuffer: integer[,dict] arg1: buffer length arg2: options: lockdown (boolean): if True, mlock() the buffer ** site Defines: site (closure => site closure) site: dict argument local-name (string): this site's name for itself name (string): the name of the site's peer link (netlink closure) comm (one or more comm closures): if there is more than one, the first one will be used for any key setups initiated by us using the configured address. Others are only used if our peer talks to them. resolver (resolver closure) random (randomsrc closure) key-cache (privcache closure) local-key (sigprivkey closure): Deprecated; use key-cache instead. address (string list): optional, DNS name(s) used to find our peer; address literals are supported too if enclosed in `[' `]'. port (integer): mandatory if 'address' is specified: the port used to contact our peer peer-keys (string): path (prefix) for peer public key set file(s); see README.make-secnet-sites re `pub' etc. and NOTES.peer-keys. key (sigpubkey closure): our peer's public key (obsolete) transform (transform closure): how to mangle packets sent between sites dh (dh closure) key-lifetime (integer): max lifetime of a session key, in ms [one hour; mobile: 2 days] setup-retries (integer): max number of times to transmit a key negotiation packet [5; mobile: 30] setup-timeout (integer): time between retransmissions of key negotiation packets, in ms [2000; mobile: 1000] wait-time (integer): after failed key setup, wait roughly this long (in ms) before allowing another attempt [20000; mobile: 10000] Actual wait time is randomly chosen between ~0.5x and ~1.5x this. renegotiate-time (integer): if we see traffic on the link after this time then renegotiate another session key immediately (in ms) [half key-lifetime, or key-lifetime minus 5 mins (mobile: 12 hours), whichever is longer]. keepalive (bool): if True then attempt always to keep a valid session key. [false] log-events (string list): types of events to log for this site unexpected: unexpected key setup packets (may be late retransmissions) setup-init: start of attempt to setup a session key setup-timeout: failure of attempt to setup a session key, through timeout activate-key: activation of a new session key timeout-key: deletion of current session key through age security: anything potentially suspicious state-change: steps in the key setup protocol packet-drop: whenever we throw away an outgoing packet dump-packets: every key setup packet we see errors: failure of name resolution, internal errors peer-addrs: changes to sets of peer addresses (interesting for mobile peers) all: everything (too much!) mobile (bool): if True then peer is "mobile" ie we assume it may change its apparent IP address and port number without either it or us being aware of the change; so, we remember the last several port/addr pairs we've seen and send packets to all of them (subject to a timeout). We maintain one set of addresses for key setup exchanges, and another for data traffic. Two communicating peers must not each regard the other as mobile, or all the traffic in each direction will be triplicated (strictly, transmitted mobile-peers-max times) and anyway two peers whose public contact address may suddenly change couldn't communicate reliably because their contact addresses might both change at once. [false] mobile-peers-max (integer): Maximum number of peer port/addr pairs we remember and send to. Must be at least 1 and no more than 5. [4 if any address is configured, otherwise 3] static-peers-max (integer): Maximum number of peer port/addr pairs we can try for a static site. Must be at least 1 and no more than 5. [4 or 3, as above] mobile-peer-expiry (integer): For "mobile" peers only, the length of time (in seconds) for which we will keep sending to multiple address/ports from which we have not seen incoming traffic. [120] local-mobile (bool): if True then other peers have been told we are "mobile". This should be True iff the peers' site configurations for us have "mobile True" (and if we find a site configuration for ourselves in the config, we insist on this). The effect is to check that there are no links both ends of which are allegedly mobile (which is not supported, so those links are ignored) and to change some of the tuning parameter defaults. [false] mtu-target (integer): Desired value of the inter-site MTU for this peering. This value will be advertised to the peer (which ought to affect incoming packets), and if the peer advertises an MTU its value will be combined with this setting to compute the inter-site MTU. (secnet will still accept packets which exceed the (negotiated or assumed) inter-site MTU.) Setting a lower inter-site MTU can be used to try to restrict the sizes of the packets sent over the underlying public network (e.g. to work around network braindamage). It is not normally useful to set a larger value for mtu-target than the VPN's general MTU (which should be reflected in the local private interface MTU, ie the mtu parameter to netlink). If this parameter is not set, or is set to 0, the default is to use the local private link mtu. comm-info (dict): Information for the comm, used when this site wants to transmit. If the comm does not support this, it is ignored. Links involving mobile peers have some different tuning parameter default values, which are generally more aggressive about retrying key setup but more relaxed about using old keys. These are noted with "mobile:", above, and apply whether the mobile peer is local or remote. ** transform-eax Defines: eax-serpent (closure => transform closure) ** transform-cbcmac Defines: serpent256-cbc (closure => transform closure) ** netlink Defines: null-netlink (closure => closure or netlink closure) null-netlink: dict argument name (string): name for netlink device, used in log messages networks (string list): networks on the host side of the netlink device remote-networks (string list): networks that may be claimed by the remote site using this netlink device local-address (string): IP address of host's tunnel interface secnet-address (string): IP address of this netlink device ptp-address (string): IP address of the other end of a point-to-point link mtu (integer): MTU of host's tunnel interface Only one of secnet-address or ptp-address may be specified. If point-to-point mode is in use then the "routes" option must also be specified, and netlink returns a netlink closure that should be used directly with the "link" option to the site closure. If point-to-point mode is not in use then netlink returns a closure that may be invoked using a dict argument with the following keys to yield a netlink closure: routes (string list): networks reachable down the tunnel attached to this instance of netlink options (string list): allow-route: allow packets coming from this tunnel to be routed to other tunnels as well as the host (used for mobile devices like laptops) soft: remove these routes from the host's routing table when the tunnel link quality is zero mtu (integer): MTU of host's tunnel interface Netlink will dump its current routing table to the system/log on receipt of SIGUSR1. ** slip Defines: userv-ipif (closure => netlink closure) userv-ipif: dict argument userv-path (string): optional, where to find userv ["userv"] service-user (string): optional, username for userv-ipif service ["root"] service-name (string): optional, name of userv-ipif service ["ipif"] buffer (buffer closure): buffer for assembly of host->secnet packets plus generic netlink options, as for 'null-netlink' ** tun Defines: tun (closure => netlink closure) [only on linux-2.4] tun-old (closure => netlink closure) tun: dict argument flavour (string): optional, type of TUN interface to use ("guess","linux","bsd","streams") device (string): optional, path of TUN/TAP device file ["/dev/net/tun"] interface (string): optional, name of tunnel network interface ifconfig-path (string): optional, path to ifconfig command route-path (string): optional, path to route command ifconfig-type (string): optional, how to perform ifconfig route-type (string): optional, how to add and remove routes types are: "guess", "ioctl", "bsd", "linux", "solaris-2.5" buffer (buffer closure): buffer for host->secnet packets plus generic netlink options, as for 'null-netlink' I recommend you don't specify the 'interface' option unless you're doing something that requires the interface name to be constant. ** privcache Cache of dynamically loaded private keys. Defines: priv-cache (closure => privcache closure) priv-cache: dict argument privkeys (string): path prefix for private keys. Each key is looked for at this path prefix followed by the 10-character hex key id. privcache-size (integer): optional, maximum number of private keys to retain at once. [5] privkey-max (integer): optional, maximum size of private key file in bytes. [4095] ** pubkeys Defines: make-public (closure => sigpubkey closure) make-public: ( arg1: sigscheme name arg2: base91s encoded public key data, according to algorithm ** rsa Defines: sigscheme algorithm 00 "rsa1" rsa-private (closure => sigprivkey closure) rsa-public (closure => sigpubkey closure) rsa1 sigscheme algorithm: private key: SSH private key file, version 1, no password public key: SSH public key file, version 1 (length, restrictions, email, etc., ignored) rsa-private: string[,bool] arg1: filename of SSH private key file (version 1, no password) arg2: whether to check that the key is usable [default True] rsa-public: string,string arg1: encryption key (decimal) arg2: modulus (decimal) The sigscheme is hardcoded to use sha1. Both rsa-private and rsa-public look for the following config key in their context: hash (hash closure): hash function [sha1] ** dh Defines: diffie-hellman (closure => dh closure) diffie-hellman: string,string[,bool] arg1: modulus (hex) arg2: generator (hex) arg3: whether to check that the modulus is prime [default True] ** md5 Defines: md5 (hash closure) ** sha1 Defines: sha1 (hash closure) ** conffile Defines: makelist (dictionary => list of definitions) readfile (string => string) map (closure,list => list) makelist: dictionary returns a list consisting of the definitions in the dictionary. The keys are discarded. readfile: string reads the named file and returns its contents as a string map: applies the closure specified as arg1 to each of the elements in the list. Returns a list made up of the outputs of the closure. * Legal This file is part of secnet. See LICENCE and CREDITS for full list of copyright holders. SPDX-License-Identifier: GPL-3.0-or-later There is NO WARRANTY.