Zebedee --- a simple, free, secure TCP and UDP tunnel program
zebedee -s [common-options] [-c host] [-C num] [-r ports] [target ...]
zebedee [-m] [-e command] [server] [tunnel-spec ...]
zebedee [-dDLtuU] [-b address] [-F char] [-f file] [-K checksumlevel] [-k keybits] [-n name] [-o log] [-T port] [-v level] [-x config] [-z level] ...
zebedee -p [-f file]
zebedee -P [-p] [-f file]
zebedee -h [file ...]
zebedee -H string ...
zebedee [-n name] -S [install[=file] | remove | run]
zebedee [-N userid] ...
Zebedee is a simple program to establish an encrypted, compressed "tunnel" for TCP/IP or UDP traffic between two systems. This allows data from, for example, telnet, ftp and X sessions to be protected from snooping. You can also use compression, either with or without data encryption, to gain performance over low-bandwidth networks.
This document describes the features of Zebedee as at release 2.5.3. For details of the new features in this release see CHANGES.
The main goals for Zebedee are to:
Provide client and server functionality under both UNIX/Linux and Windows.
Be easy to install, use and maintain with little or no configuration required.
Have a small footprint, low wire protocol overhead and give significant traffic reduction by the use of compression.
Use only algorithms that are either unpatented or for which the patent has expired.
Be entirely free for commercial or non-commercial use and distributed under the term of the GNU General Public Licence (see "CREDITS AND LEGALITIES").
Of course, Zebedee is by no means the first, or only secure tunnel program available. It does not pretend to compete with the likes of ssh or SSL in terms of breadth of function but if you want something quick, simple and completely free then it may be the tool for you.
In case you were wondering, or even if you weren't, Zebedee is named after its three main components:
Blowfish encryption and
Diffie-Hellman key agreement.
So now you know!
To set up a secure connection between your local machine and a remote host you need first to run Zebedee in server mode on the remote system. The easiest way to do this is to run Zebedee with the -s option (but please read the notes on security issues later):
If all goes well (and it should!) Zebedee will detach from the terminal (or console window under Windows) and run in the background. It will then be listening for incoming requests from clients.
On your local machine you then run Zebedee in client mode. You need to specify the name of the remote machine and the name of the service or number of the port to which the tunnel should be established --- we will call this the "target" port. If the remote machine is called
remhost and you want to set up a secure telnet session then you would run:
In fact, if you don't specify a service or port the default is telnet so
would do just as well in this instance. When you run this command it will print out a message telling you the port number which is the local end of the tunnel. Zebedee will then detach from the terminal and run in the background waiting for you to connect to the local port. If, for example, the port number it printed out was 1234 then to connect to
remhost using the secure tunnel you would run:
telnet localhost 1234
By default, Zebedee will continue to listen for connections and tunnel them, handling multiple simultaneous connections if necessary, until you terminate the process.
Sometimes you will want to start Zebedee and then run a command that connects to the port straight away. You can do this in a single invocation of Zebedee as follows:
zebedee -e "telnet localhost %d" remhost
%d" in the string is automatically replaced with the local port number so there is no need for Zebedee to print it out. If you specify a command like this then the local Zebedee client will exit once the command closes its connection.
You may want or need to control the local port number that the client uses. This is necessary if the command whose connection you are trying to protect expects to connect only to a specific port. In this case you can also specify the local port number by invoking Zebedee as follows:
So, for example, the command:
will allow you to secure all HTTP connections to webhost if accessed via port 8000 on the client system. See EXAMPLES for more details.
You can also use a single Zebedee client to handle multiple simultaneous tunnels to different target ports on the same remote host. In this case the client and target port specifications are lists of ports. For example:
This will tunnel traffic on the clientport 9001 to the daytime port on the remote target system, traffic on 9002 to the telnet port and traffic on 9003 to the ftp port.
This combination of client listening ports, target host and destination ports is called a "tunnel specification". See the tunnel keyword for more details.
Originally Zebedee was designed only to be able to handle TCP/IP traffic. It can now also handle connectionless UDP data. To enable this start Zebedee with the -U option (or use the ipmode keyword). For example:
zebedee -s -U
on the server host and
zebedee -U 10000:somehost:echo
on the client. When run in this way Zebedee will handle both TCP and UDP traffic.
The tunnel between Zebedee clients and servers still uses a TCP/IP connection even in UDP-mode. This connection is timed out after a certain period of inactivity. It must be re-established if more data arrives. For this reason the performance in UDP mode may appear poor, depending on the nature of the application using it. You should note that there is also a limit on the size of UDP datagrams that can be handled.
For further details see the maxbufsize, ipmode, udptimeout and tcptimeout keywords.
Usually there will only be two systems involved when you set up a tunnel using Zebedee. You will run a client on one and communicate with it via connections to local ports. On the other you will run a server which will speak to services local to that machine. However, there can be up to four different systems involved, as shown below:
[source] <===> [client] <=====> [server] <===> [target] | | | +- insecure | + insecure connection | connection +- secure tunnel
The Zebedee client runs on the "client" system and the server runs on the "server" host. The inital connection that causes a tunnel to be established between client and server originates from the "source" machine. This could be a different system than where the Zebedee client is running, although it is usually the same. The server will ultimately communicate with the "target" system. Again, this is usually the local machine but does not have to be.
Most of the time you will not have to be concerned with the distinction between source and client and server and target. The terminology is, however, reflected in a number of the keywords described in the following section so you should bear it in mind when reading their descriptions.
In addition to the different systems involved in Zebedee tunnel there are also several different types of keys used to secure connection. The client and server generate or are provided with private key values. These are used to calculate public values which are exchanged and used to derive a shared secret key using the Diffie-Hellman key agreement mechanism. From this shared key a unique session key is derived to secure an individual connections between client and server.
A single Zebedee client/server pair can handle tunnels for multiple targets, not just the system on which the Zebedee server is running.
When a server is started it can be given a list of valid targets either on the command-line or by using the target keyword. Each target is a host name optionally followed by a list of ports to which connections may be made. Consider the following command run on a machine called serverhost:
zebedee -s target1:daytime,telnet target2:telnet target3
the server will allow connections to the daytime and telnet ports on target1, the telnet port on target2 and any port on target3.
Given this server invocation, a client may be started as follows:
zebedee serverhost 10000:target1:telnet 20000:target3:telnet
This will connect to the Zebedee server on serverhost and use it to establish tunnels to the telnet port on target1 via the client port 10000 and tunnels to the telnet port on target3 via 20000. Note that the name of the host on which the server is running is given as the first parameter. If the server name is omitted it is determined from the first tunnel specification. So if the server had been running on target3 then the above command could have been given as:
zebedee 20000:target3:telnet 10000:target1:telnet
In fact, a server also maintains a notion of a default target. This is the host name of the last target specified. In the example server invocation above the default target becomes target3. This is the target used when the server and target names specified by the client are the same. Be careful of this because you may get results that you do not expect. For example, if the server was started on
zebedee -s target2:telnet target3 target1:daytime,telnet
then the following client invocation:
would result in connections to port 20000 being tunnelled to target1 and not target3. This is because when the server and target specified by the client are the same then the traffic goes to the server's default target. To avoid confusion, if you want to include the server host in a list of multiple destinations then always name it last. Note that as well as a default target host it is also possible to specify a list of default allowed target ports where none are otherwise given. See the redirect keyword for more details.
As with the target keyword for the server, the equivalent of the command-line parameter for the client is the tunnel keyword (and serverhost in order to specify the server host explictly).
In normal use a Zebedee client inititates connections to the server when a connection has been made to it from a source system. Sometimes, for example when using Zebedee through a restrictive firewall, it may be necessary for the server to initiate the connection back to the client --- to operate in "reverse." For details on how to do this see the clienthost and listenmode keywords.
The behaviour of Zebedee is probably best controlled through the use of a configuration file. A configuration file can be specified using the -f command-line option. The file is read at the point at which the option is encountered so later command-line options may override the contents of the file.
Lines are of the form:
keyword value # optional comment
The keyword is a single, case-insensitive word. The value is either a single word or a string. Strings are enclosed either in double quotes (
"like this") or single quotes (
'like this'). Double quotes may appear in single quoted strings and vice versa (
"here's an example"). Case is preserved in the values where appropriate.
Blank lines and lines beginning with a "
#" (after any leading whitespace) are ignored. Long strings may be continued onto the next line by ending the line with a "
\" character. This character is eliminated and the next line is joined on to the end. Note that there is a limit of a total of 1024 characters on any line and its continuations. Line continuation happens before anything else, including comment recognition so the lines:
server false # This comment continues on the next line \ server true
will leave the value of server as false.
The keywords and their meanings are as described below. There is a brief description of all the keywords in the "Quick-Reference Summary" section. Some, but not all, keywords have equivalent command-line options. These are shown where available. There are also a few command-line options that have no equivalent in the configuration file. These are described at the end of this section.
If a keyword is described as being a boolean then its value must be one of the words true or false.
Several keywords require a list of ports to be specfied. Where this the case the value is string that consists of a comma or white-space delimited list of port names, numbers or numeric ranges. For example "
telnet, ftp 5900-5903". This is equivalent to the list "
23,21,5900,5901,5902,5903". You can also specify that a particular port or range should only be used for TCP or UDP traffic by suffixing it with "
/tcp" or "
/udp". If this suffix is omitted it can be used for either type. So, the list "
telnet/tcp,daytime/udp,echo" specifies TCP-only traffic to the
telnet port, UDP-only traffic to the
daytime port and either to the
A number of the keywords are either only applicable to clients or only applicable to servers. The same Zebedee program runs as either client or server and will silently ignore inappropriate options for the current type of usage. The choice of client or server behaviour is controlled by the server keyword:
This is a boolean indicating whether the program should run as a client or a server. The default is to run as a client if this keyword is not specified. The command-line -s option is equivalent to setting this keyword to true.
This specifies the about of time, in seconds, that a server should block trying to connect to a target host. The default is 300 seconds.
The following keywords apply only to Zebedee clients:
When running as a client, this is a command that will be spawned to run connected to the tunnel. If the value contains the character sequence "
%d" this will be replaced at run-time with the local port number (see the tunnel keyword). As this is done using sprintf the conventions of that routine apply with regards to escaping "
%" characters (i.e. use "
%%" to generate a single "
%"). In addition, specifying more that one "
%d" or other format sequence will very likely crash the program.
Once the command closes its connection Zebedee will exit. Using this keyword or option implicitly turns off multi-use mode (see multiuse). You can not use automatic command spawning when a single Zebedee client is handling multiple connections in multiuse mode or when a list of ports has been specified with the tunnel keyword or on the command-line.
In normal use a Zebedee client inititates connections to the server when a connection has been made to it from a source system. Sometimes, for example when using Zebedee through a restrictive firewall, it may be necessary for the server to initiate the connection with a client --- to operate in "reverse."
The listenmode keyword, if true, causes a Zebedee client to listen for connections initiated by the server rather than to connect directly. The client will listen for connections at the network level but the connection from the server will not be fully accepted and activated until a matching connection from the source system has been received. Equally, a client will accept connections from source clients but no data will be read from or sent to these connections until a connection has been made with a server.
Normally a client makes a connection to a specific server address. Server-initiated connections could, however, originate from arbitrary addresses, thus giving the client no control over the destination of the tunnel. To avoid this the client will validate that the address of the server's connection matches that specified, whether on the command-line, via the serverhost keyword or as part of the first tunnel specification. (The client can also use the checkaddress keyword to perform such checking).
When using listenmode the server address can also contain a network mask. So the following client invocation:
zebedee -l 10000:10.10.10.0/24:telnet
will accept connections from any address on the 10.10.10.0 class C subnet. As a special case, if the server name is "
*" then connections will be accepted from any server address. Use of the identity checking features is also recommended to ensure that the correct server connects.
If a connection from a server is not received within a certain period then the connection back to the source system will be closed and the process abandoned. This timeout is controlled by the acceptconnecttimeout keyword. The default is 300 seconds.
See the clienthost keyword for the description of the server side of this process.
If this value is true then the client will only accept connections originating from the local machine. In other words the "source" system must be the same as the "client" system.
The default is for this value to be false and for connections to be allowed from any arbitrary source machine.
This has been superseded by the more generic listenip keyword. So "
localsource true" is equivalent to "
If this value is true, which is the default, then the Zebedee client will handle multiple (potentially simultaneous) connection requests and will establish a new tunnel to the server for each one. If it is false, the client runs in "single-use" mode and exits after the first connection to the server has been closed.
The command-line -m option is equivalent to setting this to true. This is the default behaviour in the current version of Zebedee and the option is retained only for backwards-compatibility reasons.
Any client listening on multiple ports will automatically run in "multi-use" mode, even if this is set false (see clientport).
This is the name of the host on which a Zebedee server is running and to which a tunnel is to be connected. There is no default and a host name must be specified either in a configuration file or on the command line.
See the listenmode keyword for the treatment of this value when using server-initiated connections.
Prior to version 2.0.0 this was known as the remotehost keyword. This is still recognised for backwards compatibility.
This is a string that consists of three parts separated by colons, for example:
The first part is the list of ports on which the Zebedee client will listen for connections. The second part is the name of the target host to which the tunnelled data should be directed. The final part is the list of target ports that correspond to the ports on which the client is listening. The numbers of entries in the client and target port lists must match.
As a special case, if only a single tunnel specification is given with only a single target port then the client port list (and separating colon) may be omitted. The client port will be assigned automatically (and a message will be printed to the terminal giving the port number). This is to allow for backwards compatibility and for use with the command keyword. If the target port is also omitted then it will default to telnet (port 23).
As described in the section "Multiple Destinations" if the Zebedee server host is not explicitly specified, either as the first argument on the command-line or via the serverhost keyword, then it will be taken from the first tunnel specification found.
There is also one final variant of the tunnel specification. In this case the targethost is replaced by a "
*". This wild-card form is used either with the client running in "listen-mode" (see listenmode for further details) or when you want to specify tunnelling to the server's default target, whatever it may be. This latter form is useful in a configuration file when you want the file to be generically applicable to any server. For example, a file like this:
server false tunnel 10000:*:daytime tunnel 20000:*:echo tunnel 30000:*:telnet
can be used to set up tunnels on ports 10000, 20000 and 30000 to whatever host may be specified on the command-line like this:
zebedee -f configfile serverhost
The following keywords apply only when running as a server:
If a clienthost value is specified then the server will immediately attempt to connect to the specified host (on the port given by serverport). Once a connection to the client has been established the protocol exchanges proceed as normal. Each time a connection has been accepted by the client the server tentatively opens up another one so that the client could establish further tunnels if necessary.
Three other keywords affect this behaviour. The serverconnecttimeout keyword determines how long the server will spend trying to make a connection. If it cannot immediately connect to the client it will wait this many seconds before trying again. Once a connection has been established the server will wait up to acceptconnecttimeout seconds for the client to accept the connection and start the protocol exchange. Finally, this whole process will be repeated up to connectattempts times. If a connection is not opened and accepted within this number of attempts the server will exit once all currently active tunnels have been closed.
Note that Zebedee does not itself provide a mechanism for co-ordinating the starting of client and server to set up a "reverse" tunnel. That must be handled by some "out-of-band" mechanism.
This specifies the number of attempts the server makes to connect back to a client when a clienthost is given. The default is 1.
This is a boolean indicating whether a Zebedee server should attempt to continue negotiating a connection with a client that requests a version of the Zebedee protocol that the server can not support. By default this is false, meaning that the server will reply with the highest protocol version it supports, allowing the client to decide if it can continue. If set to true, the server will immediately terminate the connection.
See also lockprotocol.
This is the default list of the ports on the target system to which the server will accept requests to redirect data, when the target specification does not otherwise specify a port range. An example port list might be "
telnet, ftp, 5900-5910".
If no redirect keyword is specified then requests to redirect traffic to any port will be accepted. While this is convenient for testing it may pose a security risk so you should specify an explict list of allowed ports if at all possible. As a special case, if the port range is given as "
none" then any current default redirection list will be cleared and no target ports will be accepted by default.
The keyword (or -r option) may be specified multiple times in which case redirection will be allowed to any of the ports specified.
It is generally better to use the target keyword instead of redirect, where possible. The main reason to prefer redirect is when you want to specify a common range of ports for a number of targets, for example:
# Set up common target redirections redirect telnet,ftp,daytime target hosta target hostb target hostc # Set up additional host-specific redirections target hostb:http
This specifies a target host and, optionally, list of ports to which a server will accept requests to redirect data. It is a string consisting of the target host name followed by a colon and then a list of ports. For example
If the port list (and colon) are omitted then requests for redirection will be controlled by the ports given by the redirect statements, if any.
The target hostname may also be specified as a CIDR network address, that is an address with the number of bits to be used for the network mask, for example:
This means that HTTP connections to any host address in the 255-host class C subnet will be accepted.
This keyword is equivalent to the comnmand-line arguments of the same form (see "Multiple Destinations"). It may be repeated multiple times. The final target host specified, either using the this keyword or on the command line, becomes the default destination for tunnels when a client specifies the server's host-name as the destination.
Be careful when using CIDR addresses as targets that the last target specified will be valid default address. If the default target has an address mask then Zebedee will flag this as an error and exit.
It is also possible to apply identity checking and source IP address validation, like that provided by checkidfile and checkaddress, to individual targets. If the target is suffixed with a "
?" followed by a file name, such as this:
then the file (
httpusers.ids in this example) must be a file in the same format as that described in the identity checking section. The effect of this target specification is to allow connections to be created to the HTTP port of any machine in the 10.10.10.0/24 sub-net, but only by clients whose identities are found in
Similarly, the target can be suffixed with "
@" followed by an address specification in the same form as that used by checkaddress. For example:
In this case only clients in the 10.20.30.0/24 sub-net will be permitted to create tunnels to this target.
You can't combine both the "
?" and "
@" forms. But you really wouldn't want to do that anyway, would you?
This sets maximum timeout for server attempting to make a connection to a target endpoint. Normally a connection attempt will fail immediately if there is no target server running. However, with certain kinds on network or system failures connection attempts can block almost indefinitely. This timeout prevents these hangs. The default is 300 seconds.
This is a boolean value, which is false by default. If set true it causes the Zebedee server to attempt to propagate the client's IP address to the target server --- for the existence of the server to become "transparent".
This functionality will not work on all platforms and Zebedee will have to be run as a privileged user (e.g.
root on UNIX-like systems) in order for it to work at all. Full transparency support for TCP and UDP traffic is currently only expected work on Linux and then only on systems with kernel versions 2.0 and 2.2. It will not work on Linux 2.4, although there is some hope that it may work in future versions.
Support for a limited form of transparency for UDP traffic is available for a wider range of UNIX-like platforms, although this must have been enabled at compile time (it is not enabled by default in the "standard" builds). If it has been enabled then unidirectional UDP traffic from client to server will preserve the Zebedee client's IP address on datagrams sent to the target server. This will be sufficient for applications such as
syslog where there is no requirement that the target server should reply to such traffic. Applications that attempt to reply to the address in these datagrams will not send replies via the Zebedee tunnel and, in fact, are likely to send their data to non-existent or invalid endpoints.
The following keywords control the compression, encryption and checksumming of data passing through the tunnel. They apply to both clients and servers:
Zebedee will, by default, calculate a checksum for every message sent over the tunnel. This checksum is appended to the message and verified by the recipient. If the checksum calculated by the recipient does not match that in the message the tunnel connection will be terminated. You should note that for the checksum to be effective as a means of assuring that data has not been maliciously modified, you should ensure that the data is also encrypted.
The checksumlevel is an integer between 0 and 3 that determines the checksumming algorithm used to check the integrity of data transferred by Zebedee. The default is 2. This provides a reasonable level of assurance, at the price of a 4-byte overhead on each message and some extra computation. Setting this to 0 turns off checksumming (which was the behaviour prior to Zebedee version 2.5).
The checksum level used will be the minimum of the client's and server's values (subject to any setting of minchecksumlevel).
The algorithms used and the overhead they imply are as follows:
No checksum, no additional overhead.
This uses the
ADLER32 algorithm from zlib. It requires a 4-byte overhead per message. The algorithm is fast but gives the lowest degree of assurance that the message has not been modified or corrupted in transit.
This uses the
CRC32 algorithm from zlib. It requires a 4-byte overhead per message. This is a little slower than
ADLER32 but provides a better level of assurance of the data integrity.
This uses the
SHA algorithm. It requires a 20-byte overhead per message. This is the most CPU-intensive operation but provides a very high degree of assurance that the contents of the message have not been altered in transit.
Zebedee can support both zlib and, if enabled when it is built, bzip2 compression. This keyword specifies the type and level of compression to be used. The value is of the form type:level where type is either "
zlib" or "
bzip2" and level is an integer from 0 to 9. As a special case an integer without any prefix implicitly selects a zlib compression level.
The level specifies the maximum compression level to used (9 is the maximum and 0 is no compression). The actual compression level used will be the minimum of the client's and server's values. For these purposes all bzip2 levels (except 0) are considered to be greater than all zlib levels so if either client or server does not support bzip2 the protocol degrades gracefully to using zlib. The default compression value is "
Note that, because of the way that bzip2 compression works and the buffer sizes that Zebedee uses, bzip will probably only be useful if continuous streams of data are flowing. On smaller transfers, such as those in a normal telnet session, zlib will usually win. You will have to experiment to see what works best for you. In addition, because the buffer size is small there is no gain from using bzip2 levels above 1 and Zebedee will round any higher values down to this level.
You can see exactly how much compression is gaining you at verbosity levels 2 and above when basic statistics are printed out on connection termination. For example:
zebedee(232/210): read 166 bytes (265 expanded) in 3 messages zebedee(232/210): wrote 20969 bytes (30499 expanded) in 247 messages
This is the "generator" for the Diffie-Hellman key exchange and is a hexadecimal string. The default value is "2". I recommend that you don't mess with this unless you know what you are doing.
If this keyword is specified its value is a command string that will be executed in order to generate a private key (see privatekey. The command should write a single line of hexadecimal digits to stdout. This line must be a string of at least 10 hexadecimal digits. A simple Tcl (see http://tcl.activestate.com) script (
passphrase.tcl) that prompts a user for a pass-phrase and then uses this to generate an appropriate key is included in the standard Zebedee distribution. If might be used as follows (
wish is the Tcl script interpreter):
keygencommand "/usr/bin/wish -f passphrase.tcl"
If a privatekey value is specified it takes precedence over any keygencommand.
If the command string ends with a "
+" character then the command will be run with three extra command line arguments. The first is IP address of the system to which the tunnel is connected (the server address for a client, and client for a server). This is in numeric form, not the DNS name. The next argument is the IP address of the target for the tunnel (note that if this is the default target it will be given as 0.0.0.0). The final argument is the target port number. So, for a Zebedee client run like this:
zebedee -x "keygencommand 'newkey -x +'" 1000:192.168.100.100:23
the key generation command run would be as follows:
newkey -x 192.168.100.100 0.0.0.0 23
This is an integer between 0 and 2 inclusive that determines how strong the private key generation in Zebedee should be. The default is 2 (the strongest) and you should generally not change this unless connection set-up performance becomes unacceptable.
Briefly, on UNIX-like systems the level-2 key generation mechanism uses
/dev/random, if either of these devices is available, to obtain good pseudo-random data based on the state of the running kernel. If no random-data device is available or the level is set to 1 then data from the current contents of the
/proc file-system, if there is one, will be used otherwise at level 0 only data from the current process will be used.
On Windows systems there is currently no distinction between different key generation strength levels and this keyword is effectively ignored.
This is an integer specifying the maximum key length (in bits) for the Blowfish encryption. It should be a multiple of 4 between 4 and 576. The key length used will be the minimum of the client's and server's values (subject to any setting of minkeylength).
The default value is 128. As a special case setting this value to 0 will turn off key negotiation and encryption.
If the value of this parameter is non-zero it causes the client to request the re-use of a previously established shared secret key for deriving session keys for subsequent connections. This means that on the first connection between a Zebedee client and server the full key exchange dialogue will take place to establish a shared secret key. On subsequent connections, until the key expires, the same secret key will be reused to generate a new session key. Once the key expires a new key exchange will automatically be performed when necessary.
This keyword specifies how long a shared secret key is valid before it must be renegotiated. This does not affect connections that have already been established, only new connections.
The value is in seconds and must be less than or equal to 65535, which is a little over 18 hours. By default it is set to 3600 seconds (one hour). Setting this value to zero effectively disables the use of reusable keys and a full negotiation of a shared key will be performed for each connection --- assuming that both client and server also generate a new private key each time. This will impact performance and is recommended only if you have a very high paranoia level!
If supplied, this specifies the minimum acceptable checksum level (see checksumlevel) to be used by the client or server. If a client requests a lower level of a server the server will reply with this minimum. If a server replies with a lower level to a client then the client will terminate the connection.
The default value is zero.
If supplied, this specifies the minimum acceptable key length (see keylength) to be used by client or server. If a client requests a lower level of a server the server will reply with this minimum. If a server replies with a lower level to a client then the client will terminate the connection.
The default value is zero.
The value of this key is a hexadecimal string specifying the modulus value for the Diffie-Hellman key exchange. Don't alter this unless you are both paranoid and know what you are doing.
The default modulus is the 1024-bit prime:
f488fd584e49dbcd 20b49de49107366b 336c380d451d0f7c 88b31c7c5b2d8ef6 f3c923c043f0a55b 188d8ebb558cb85d 38d334fd7c175743 a31d186cde33212c b52aff3ce1b12940 18118d7c84a70a72 d686c40319c80729 7aca950cd9969fab d00a509b0246d308 3d66a45d419f9c7c bd894b221926baab a25ec355e92f78c7
This was taken from the file testdh.h in Peter Gutman's CryptLib. The comment in this code says that the value was among those "generated by Colin Plumb for SKIP". It further says that "these values were chosen as representative well-known public values to allay fears of possible trapdoors in self-generated values. The generation method and actual values can be checked against the SKIP standards document."
By default Zebedee will generate a new private key (the "exponent" value in the Diffie-Hellman key exchange calculation) each time one is required. If, however, you wish to use a fixed key then it can be specified as a string of hexadecimal digits. You will definitely need to do this if you wish to use the identity checking feature. Note that the key must be at least 10 digits long.
By default Zebedee uses the Diffie-Hellman key exchange protocol to establish an anonymous, shared secret key between client an server. This means that neither party has to store any permanent secret key. However, under some circumstances you may wish to use a pre-established shared secret key, communicated by other means. The sharedkey keyword allows you to do this. Its value is a string of hexadecimal digits. This value is the unencrypted shared key and it must contain at least as many bits (there are 4 bits per digit) as will be used to encrypt the traffic through the tunnel. Note that the shared key is not, however, used to encrypt the data directly. A unique session key is still established for each tunnel.
All clients and servers that wish to communicate must use the same shared secret key value. Connections between clients and servers that do not share the same secret will be terminated before a tunnel is established. It is your responsibility to distribute and protect this secret from disclosure.
This is the equivalent to the keygencommand but in this case generates a sharedkey value. Any sharedkey value overrides this, if present.
The following keywords apply equally to clients and servers:
This keyword, which may be repeated multiple times, specifies an IP address and, optionally, range of ports in the same form as that used by the target keyword. The IP address can be in the form of a CIDR address.
When a connection is established between a client and a server the IP address and, optionally, source port of the system at the other end of the connection is checked against the set of specified addresses and ports. If it does not match any of the entries the connection will be closed. So, for example, the entry:
checkaddress 192.168.1.0/24 checkaddress 192.168.2.0/24
in a server's configuration file would only permit connections from systems on the two subnets named. This checking is done before any further validation of identity (see identity checking).
Please note that source IP addresses can easily be "spoofed" and you should not place great reliance on this for validating the identity of a client or server. It is, however, a useful basic protection mechanism.
This names a file that contains a set of identities that will be checked before allowing a connection to be completed. This is described further in the description of identity checking. You may specify only one identity file. If this keyword appears multiple times only the last value will be used.
If a keylength of zero has been agreed then no identity checking will be performed.
When Zebedee is used in "reverse-mode" (see listenmode and clienthost) the timeout on waiting for connections to be accepted is controlled by this keyword. Its value is in seconds and may be no greater than 65535. The default is 300 seconds.
This is a boolean indicating that Zebedee should run in "debug" mode. In this case a server (or client running in multiuse mode) only accepts and handles a single connection at a time and does so "inline" without creating another process or thread. This is useful when running the program under the control of a debugger. It is false by default. The command-line option -D is equivalent to setting this to true.
Note that this setting will not work correctly in UDP mode, so don't bother trying it!
This is a boolean indicating whether the process should detach itself from the controlling terminal and run in the background (in UNIX terms, to run as a "daemon"). This is valid for both client and server and is true by default. The command-line option -d is equivalent to setting this to false.
Note that this does not always seem to work from an interactive command prompt under Windows systems. The symptom is that output to the console window will stop and interrupt signals will be ignored but the console prompt will not be issued until Zebedee terminates. In order to work around this you can use the "start" command as in the following example:
DOS> start zebedee -f server.zbd
This will start Zebedee in a new console session from which it will then detach. You may see a console window appear briefly before it detaches but Zebedee should be running in the background when it disappears.
This is a boolean value indicating whether logging output should include details of the data sent to and received from local sockets. Because this data is potentially sensitive --- one of the reasons for using Zebedee in the first place --- the default is for such data not to be included (dumpdata is false). If it is set to true then, when the verbosity level is 5 or greater, the logging output will include lines such as the following:
read 39 bytes from local socket 324 < 0000 00 00 00 # ff S M B a2 4 00 00 c0 98 07 c8 < 0010 00 00 00 00 00 00 00 00 00 00 00 00 01 08 d0 03 < 0020 01 08 p 00 00 00 00
Lines beginning with "
<" or "
>" show the data that is being is read from or written to the local socket. Each line shows up to sixteen bytes of data and is prefixed by the offset, in hexadecimal, from the beginning of the data stream. Printable ASCII characters are shown verbatim, such as the three characters "
SMB" above, while other bytes are shown as a hexadecimal value.
Zebedee now has support for making the client-server TCP connection via an HTTP proxy. If specified this should give the address and port of the proxy server, for example:
There is no default port, you must always specify one explicitly. The proxy can be used for either client or server-initiated connections (see listenmode). Source or target connections are unaffected, the proxy only applies to connections between a Zebedee client and server.
Please note that using an HTTP proxy server to tunnel arbitrary connections is very likely to violate the security policy of the organisation running the server. If you intend to use Zebedee in this way (or, for that matter, to establish any other kind of "backdoor" tunnel) I strongly advise you to seek permission from the appropriate network administrators.
In order to give administrators some chance to maintain proper control over the use of their proxy servers Zebedee does identify itself with a user-agent string of
Zebedee when it connects to the proxy server. Well, it does in the "official" version anyway.
If tunnelling via an HTTP proxy, using httpproxy, some proxy servers require authentication information to be supplied in order to permit the connection to be made. Zebedee supports the "basic" authentication type. The username and password required for this can be specified using the httpproxyauth keyword. The username and password are given in plain text, separated by a colon, as follows:
This sets both the tcptimeout and udptimeout to the same value, causing idle connections to be closed. Please see those keywords for further details.
This specifies the name of another configuration file to read and parse at this point before continuing with the remainder of the file. It might be used, for example, where a private key is stored in a separate, more tightly protected file. There is a limit of 5 levels deep of include processing (counting the initial configuration file as level 1). This avoids unintentional recursion.
As of version 2.4, a Zebedee client or server can handle both TCP and UDP traffic simultaneously. This is controlled by the ipmode keyword. It can have a value of tcp, udp or both.
The default value is tcp and Zebedee will only handle TCP traffic in this case. The value udp is equivalent to setting udpmode to be true. In this case only UDP traffic will be handled and the Zebedee server will, by default use a different port (11230). If it is set to both then a client will listen for both TCP and UDP traffic and a server will handle requests to tunnel both TCP and UDP traffic. In this case the server uses only one port, by default the normal TCP-mode port of 11965. The command-line option -U is equivalent to "
Please be aware that a client or server running purely in UDP mode will expect to use port 11230 by default. If the corresponding Zebedee server or client is running in "mixed" mode you may have to specify the port explictly. For example, if the server is running in mixed mode:
zebedee -s -U
then a client running in UDP-only mode will need to specify the server port:
zebedee -u -T 11965 10000:serverhost:echo
Specifies the local IP address used to listen for connections. This can be useful on a system with multiple network interfaces, but where Zebedee should only use one of them. If listenip is not specified the default is to listen on all of the system's interfaces.
The address can be given as a "dotted quad" or by name but in the case where the name can resolve to multiple IP addresses the results may be unpredictable. The address must, obviously, also correspond to one of those belonging to the system.
Note that listenip is a more general form of localsource and setting localsource will override listenip and vice versa.
In normal usage, different versions of Zebedee will try to negotiate a compatible version of the Zebedee protocol between themselves. Provided that no incompatible features are used, all versions of Zebedee from 2.0 onwards can interwork with eachother.
The lockprotocol keyword is a boolean value that, if set true, causes a client or server to reject requests for protocol versions that do not match the default version being used by the program. The default protocol version is always the highest that the program supports so this has the effect of stopping the protocol being "downgraded" to a previous version.
The main reason for using this is to ensure that features only available in later versions of the protocol, such as checksumming of data introduced in Zebedee version 2.5, can not be silently dropped.
The default value is false.
This specifies the size, in bytes, of the buffer Zebedee will use to read data from applications. The actual size of buffer used will be the minimum of the client's and server's values.
By default Zebedee attempts to read data from the client or server programs at each end of the tunnel in chunks of 8192 bytes. There may be occasions when you want to decrease this if, for example, you have a highly interactive application and the response seems sluggish because you end up waiting for large data transfers. You can reduce the buffer size to one byte, but unless you are trying to debug misbehaviour or have time to waste I don't recommend it! Conversely, you may increase the buffer size up to a maximum of 16383 bytes to attempt to gain the most from data compression where large blocks of data are being transferred. Note that the maxbufsize value does not affect how much memory is allocated by Zebedee, only the size of data chunks read.
When running in UDP mode this buffer size will also affect the maximum size of any datagram that can be handled. Datagrams larger than the current buffer size will be fragmented, which will likely cause whatever application is consuming them to fail. Datagrams larger than 16383 bytes can not be handled at all.
This specifies that maximum number of concurrent connections (tunnels) that the Zebedee instance will handle.
The default value is zero, which means that no limit is applied. =item message
The specifies a string that will be logged at verbosity level 1 when it is encountered in the configuration file.
This is the name of the program that is to be used in messages rather than the executable file name. Under Windows it is also the name of any service to be installed or removed.
This is the name of the file to which messages will be written. If it is not specified then messages are written to stderr.
Two special "file names" are also recognised as valid values. If the name is NULL the all messages will be turned off. If the name is SYSLOG then messages will be written to the host system log. On Windows systems this is the system application event log. Elsewhere messages are written to the syslog service.
The readtimeout keyword is primarily intended to help provide a Zebedee server with some additional defence against "denial of service" attacks where a malicious user might make connections to a server but not send any data to them. Each connection consumes resources and it might be possible for an attacker to crash the server by exceeding its resource capacity.
This value represents a time limit in seconds within which reads from a Zebedee tunnel must be complete. If the value is zero then no timeout is applied. This is the default behaviour because applying a timeout will have some impact on performance and an unnecessarily small timeout may cause valid connections to fail.
The timeout primarily affects the initial Zebedee protocol exchanges. If you wish to cause valid but apparently idle connections to be timed out you should use tcptimeout or udptimeout.
This value may also be useful when a client is running in listenmode. While Zebedee tries to determine whether a connection from a server will be usable, and if it has already been closed, this is not always possible. In this case setting this to a non-zero value will stop the client hanging if it accepts such a "dead" connection.
This keyword and option apply to UNIX/Linux systems only.
It may sometimes be necessary to run Zebedee as
root (UID 0), for example so that a server can listen on a so-called "privileged" port below port 1024, or to access configuration or log files that should not be readable by other users. However, having a program, and particularly a network server, run as
root for longer than necessary is a potential security risk. If Zebedee is run as
rootL then this keyword can be used to specify a user identity to which Zebedee should switch after it has opened all files and set up listening sockets.
The user identity specified as an argument should be the name of a valid account on the host machine. For example:
Zebedee will switch to the user-ID and primary group-ID associated with that account. Note that it is considered a fatal error if the account does not exist. This protects you against Zebedee failing to switch away from
root if you were expecting it do so. If Zebedee is not running as
root a warning will be issued and the keyword ignored, but it will not cause a fatal error.
WARNING: Please note that it is not safe to make Zebedee a setuid
root program, even if this keyword is used. This keyword is only intended for use where Zebedee is run by
root. Making Zebedee a setuid
root program will open a gaping security hole in your system!
This is the port on which the Zebedee server will listen for tunnel connections. The default is 11965 (0x2EBD) when running in TCP mode or mixed TCP and UDP mode. It is 11230 (0x2BDE) in UDP-only mode. The keyword causes a server to listen on this port and a client to attempt to connect to this port on the server system.
If using server-initiated connections (see listenmode and clienthost) then this is also the port on which the client listens for the server's incoming connections.
This sets maximum timeout for a client attempting to make a connection to a server or (if running in "reverse" mode) for a server to connect back to a client. Normally a connection attempt will fail immediately if there is no remote Zebedee process running. However, with certain kinds on network or system failures connection attempts can block almost indefinitely. This timeout prevents these hangs. The default is 300 seconds.
By default, TCP-mode tunnels will stay open until either the connection is closed by either source or target. This keyword allows them to be closed after a certain period of inactivity. The value is in seconds and must be no greater than 65535. Setting it to zero results in an indefinite timeout.
See also idletimeout and udptimeout.
This specifies the size of the stack allocated to each thread in Zebedee, in units of 1 kilobyte. By default it is set to 64, and Zebedee creates threads with a 64k stack. This should be more than sufficient for its needs, and that of the C run time library. If you suffer from inexplicable crashes you may wish to try raising this. Conversely, on some platforms you may be able to lower it without causing problems. Previous versions of Zebedee have run successfully with a value of 32k. Under no circumstances can it be lowered below 16 (kilobytes).
This is a boolean value indicating whether log messages should contain a time-stamp. The default is not to do so. The command-line option -t is equivalent to setting this to true.
By default Zebedee handles connection-oriented TCP/IP traffic. If this keyword is set true Zebedee handles UDP/IP connectionless traffic instead.
The tunnel between Zebedee clients and servers still uses a TCP/IP connection. A separate connection is established for each different originating UDP network endpoint. Because UDP is connectionless there is no easy way to tell when the data traffic has been completed. For this reason the Zebedee connection must be timed out after a period of inactivity. This period is controlled by the udptimeout value.
If more data subsequently arrives from a source the tunnel for which has been timed out, the connection must be re-established. For this reason the performance in UDP mode may appear poor, depending on the nature of the application using it. Altering the keylifetime value may improve this by minimizing connection setup times and changing the udptimeout value may also help.
The command-line -u option is equivalent to setting this to true. It is also equivalent to setting ipmode to udp.
By default, UDP-mode tunnels will shut down after 300 seconds of inactivty. They are recreated automatically if any further traffic arrives. The timeout value can be changed by using this keyword to specify the timeout in seconds. It must be no greater than 65535. Setting it to zero results in an indefinite timeout. This is probably not a good idea for UDP traffic as it means that there is no way ever to indicate that those connections should be closed.
See also idletimeout and tcptimeout.
This is an integer specifying the level of message logging with 0 being just error messages and 5 giving excruciating detail of the message traffic. The default (and generally most useful level) is 1.
Messages are written to stderr (unless redirected using the -o command-line option or logfile keyword). The general form of messages is something like:
zebedee(54/119): Listening on local port 1172
The numbers in brackets represent the process and thread identifiers of the code logging the message. All error messages are logged at level 0 and are preceded by the word
ERROR, as follows:
zebedee(54/119): ERROR: failed to connect to localhost:11965
Messages are indented according to the level at which they are logged.
As Zebedee has evolved over time some of the keywords have been changed to reflect this. In a few cases keywords have been superseded and made obsolete. These obsolete keywords are still recognised in order to retain backwards compatibility with old configuration files but they should not be used in new ones.
This keyword has been superseded by the more general tunnel keyword.
This is the port or list of ports on which the Zebedee client will listen for connections. It is equivalent to the first part of a tunnel specification.
This has been replaced by the acceptconnecttimeout keyword.
This was the name of the clientport keyword prior to version 2.0.0 of Zebedee.
This was the name of the targethost keyword prior to version 2.0.0 of Zebedee.
This was the name of the targetport keyword prior to version 2.0.0 of Zebedee.
This keyword has been superseded by the more general target keyword.
This keyword gives the name of a host to which a Zebedee server will redirect all incoming tunnelled data, rather than to ports on the local machine.
This keyword has been superseded by the more general tunnel keyword.
It gives the port or list of ports to which the client will request that Zebedee server should establish connections on the target host. It is equivalent to the final part of a tunnel specification.
There are a few command-line options that have no equivalent in the configuration file. These are described below.
The first character of the argument to this option specifies an additional field separator character, used in parsing configuration file option lines. All instances of this character will be replaced with a space before lines are parsed. It exists primarily to be used in conjunction with the -x option where there may be difficulties in constructing and invoking commands containing spaces, owing to limitations in command interpreters. So, for example, the command:
zebedee -F~ -x "message~'Hello,~World!'"
will output a message like the following:
zebedee(1128/1348): Hello, World!
Please be aware that you can specify any character as a separator. It is your responsibility to ensure that the character you choose does not conflict with any other usage in the configuration file.
This causes Zebedee to generate a private key value and to write it to standard output in a form that can be used in a configuration file (see privatekey). For example:
This causes Zebedee to generate a public "identity" suitable for use by the identity checking feature. The result is written to standard output. For example:
This option must either be specified with a configuration file that contains a private key value or must be used in conjunction with -p to generate private and public keys simultaneously.
This option causes the remaining command-line arguments to be treated as the names of files. Each file is read in 8192 byte chunks and the SHA hash is calculated. If no arguments are specified or the argument is "
-" then the standard input is read and the hash of that is calculated. For example:
$ zebedee -h /etc/passwd bb1e734aeffd2111417761f5938dea3b53759598 /etc/passwd $ zebedee -h < /etc/passwd bb1e734aeffd2111417761f5938dea3b53759598 -
This is similar to the -h option except that each argument is treated as a literal string and the SHA hash of the string is calculated and printed:
$ zebedee -H hello world ac62a630ca850b4ea07eda664eaecf9480843152 hello 86bf25ecb8a40b40b885c097c683b6e236fc8085 world
On Windows systems Zebedee can be installed and run as a "service" --- an independently running process that is started automatically at system boot time.
Zebedee can be installed as a service by specifying the install parameter with the name of a configuration file, for example:
You should always specify the full path to the configuration file. This will be read at service start-up and must contain all the parameters required for the service to run. Note that if the path contains spaces you must enclose it in double quotes, as shown.
By default, the name of the installed service will be taken from the name of the program file, and hence is usually zebedee, but you can change this by using the -n option:
zebedee -n "Zebedee Client Service" "-Sinstall=c:\zebedee\clientsvc.zbd"
Once the service has been installed it will be automatically started the next time that the system reboots. Alternatively you can start it manually using the Service Control Panel (under Windows NT).
To remove the service specify first stop it and then use the remove parameter to the -S option, along with any necessary service name using -n. For example:
zebedee -n "Zebedee Client Service" -Sremove
There is one further valid parameter to the -S option and this is run. This is used internally by Zebedee to invoke the service start-up code and should not be used directly.
This option can be used to set those configuration parameters that do not have any other direct command-line equivalent. It takes a string as an argument and this string is treated as if it were a line read from a configuration files (including comments but without "\" line continuation). So, for example:
zebedee -x " server true # It's a server!"
is a rather perverse way of achieving the same effect as:
The following table lists the recognised keywords, their argument types, command-line equivalents, validity for client, server or both and a brief description.
acceptconnecttimeout seconds CS Timeout for connections to be accepted checkidfile filename CS Checks peer identities against this file checksumlevel level -K CS Sets data integrity checksum level (0 to 3) clienthost hostname -c S Server initiates connection to client host command string -e C Specified command to run connected to tunnel compression level -z CS Requested maximum compression level connectattempts number -C S Number of attempts to connect to client debug boolean CS Run in single-threaded "debug" mode detached boolean -d CS Detach from the terminal/console dropunknownprotocol boolean CS Drop requests for incompatible protocol generator string CS Hexadecimal Diffie-Hellman generator value httpproxy host:port CS Make connections via the given HTTP proxy httpproxyauth user:pass CS SUpply HTTP proxy authorisation details idletimeout seconds CS Inactivity timeout for all tunnels include filename -f CS Read in the named configuration file ipmode type -U CS Run in TCP, UDP or "both" mode (-U = both) keygencommand string CS Command to run to generate key keygenlevel level CS Key generation strength level (0 to 2) keylength bits CS Requested maximum keylength in bits keylifetime seconds CS Lifetime of shared secret keys listenip address -b CS Listens only on the specified IP address listenmode boolean -l C Client listens for server connections localsource boolean C Only accepts connections from local machine lockprotocol boolean CS Allow only current default protocol logfile filename -o CS Set the output log file maxbufsize bytes CS Specify buffer size for data reads maxconnections num CS Specify maximum number of active connections message string CS Output the specified string minchecksumlevel level CS Acceptable minimum checksum level minkeylength bits CS Acceptable minimum keylength in bits modulus string CS Hexadecimal Diffie-Hellman modulus value multiuse boolean -m C Handle multiple connections name string CS Specify the name of the program privatekey string CS Hexadecimal private key string redirect ports -r S Ports to which server will redirect traffic runasuser user -N CS Switch to if running as root (UNIX only) server boolean -s CS Selects server-mode or client-mode serverconnecttimeout seconds CS Timeout for connection to server serverhost hostname C Name of server host to which to connect serverport port -T CS Set the port on which the server listens sharedkey string CS Hexadecimal shared secret key string sharedkeygencommand string CS Command to run to generate shared key target spec S Specifies allowed target host and ports targetconnecttimeout seconds S Timeout for connection to target tcptimeout seconds CS Inactivity timeout for TCP tunnels timestamplog boolean -t CS Add timestamps to the log file tunnel spec C Specifies client ports and matching targets udpmode boolean -u CS Handle UDP traffic only udptimeout seconds CS Inactivity timeout for UDP tunnels verbosity level -v CS Set the message logging level
Other options that have no keyword equivalents:
-F char Specify an additional field separator (whitespace) character -p Generate a private key -P Generate a public "identity" -h file ... Hash file contents and print results -H string ... Hash string arguments and print results -Sinstall=file Install Windows service with specified configuration file -Sremove Remove Windows service -x string Parse option string
By default Zebedee just establishes an encrypted channel between two points. While you know that the data is protected from snooping "on the wire" there is no guarantee that the tunnel ends up where you think it does. By default, and unless you are applying any other kind of filtering or firewalling, a Zebedee server will accept connections from any client that can reach it. If the service to which you are tunnelling does not provide any further authentication, or if it relies on checking the source IP address, then it will be potentially open to attack.
The simplest, but most basic check, that you can make is to restrict the IP addresses from which a server will accept, or to which a client will make, connections. You can do this by using the checkaddress keyword.
IP address checking is useful but not that secure. Zebedee is also open to open to "man-in-the-middle" attacks where an eavesdropper pretends to a client to be the server and intercepts all traffic before forwarding it on to the real server. If you are concerned primarily with using data compression or protecting against casual "network sniffing" then you may be happy with this situation. If, however, you want more assurance that your connection is not being "hijacked" then Zebedee provides some basic facilities for doing so.
A Zebedee server can validate the identity of the client at the other end of a tunnel provided that you are using an encrypted connection. To do so the client must use a fixed private key. The easiest way to generate such a key is by using the -p option, like this:
This will output a line something like this:
The string of hexadecimal digits will be different every time you run it. So, on your client system you should generate a key and save it in a file, for example:
zebedee -p > myclient.key
myclient.key now contains the private key that will be used by Zebedee on this system. The private key must be kept secret so you should apply appropriate protection to this file to stop unauthorised users accessing it. You now need to generate the public "fingerprint" associated with this key, which you can do as follows:
zebedee -P -f myclient.key > myclient.id
The contents of the file
myclient.id will look something like this:
The text after the string of hexadecimal digits will be the name of the machine on which you run this. It's just a descriptive tag so you can change it to be, for example:
135f04050961d37553731250d5c6f7495f088b32 Neil's PC
You should now modify your client configuration file to add a line:
path-to-dir" is the directory in which the key file is being kept. The
myclient.id file is used by any server that wishes to validate the identity of
myclient. The contents are not secret and you should copy this file to the Zebedee server.
On the server you should add the contents of
myclient.id to a single file containing the identity "fingerprints" of all clients you wish to validate. This file, for example called
client.idlist, might look like this:
ba077f6a42bea502f517cab5685e476a713d9621 Rebecca's PC 3ad38cb1f16957d5c535272ce27557bdaa4389c6 Ben's PC 135f04050961d37553731250d5c6f7495f088b32 Neil's PC
Now, to the server configuration file add the following line:
That's it! Now only clients whose identities appear in this file will be able to create tunnels to the server. If you remove a line the client will be denied further access.
At the moment you can only have a single identity file and it is an "all or nothing" mechanism --- a client can either create a tunnel to any valid target or to none at all. This may be enhanced in future.
It is also worth noting that this mechanism can equally well be used for a client to validate the identity of a server, if the server uses a fixed private key.
By default, Zebedee generates a new private key every time it is started. If the same modulus, generator and private key are used they will always generate the same public value for use in the Diffie-Hellman key exchange protocol. The "fingerprint" is a hash of the modulus, generator and public key. Only a person knowing the private key will be able to produce public key and successfully decrypt traffic. So, if the same combination of modulus, generator and key are seen then the identity of the client can be tied to the owner of that private key. The modulus, generator and key strings are hashed together to produce the fingerprint merely for convenience and to keep the size of the identity file small.
Starting with version 2.5, Zebedee has the ability to perform data integrity validation on the transmitted data stream. This is controlled by the checksumlevel and minchecksumlevel keywords. This integrity checking is on by default (although not set to the highest level).
This integrity checking does give a greater assurance that data packets have not been corrupted "in flight", but is does add a little overhead in terms of both data traffic and CPU effort.
One possible attack on many networked systems is that of capturing data streams that have a known effect --- for example, a telnet session during which an administrator was known to be performing certain "dangerous" actions --- and then replaying it at some later time. This does not require cracking the encrypted data stream itself, merely knowing that the same network packets sent to a server will elicit the same response.
When Zebedee is operating in "anonymous" mode the risk of such an attack being successful is low because different private keys will be generated every time Zebedee is used. However, if the identity checking features are used the keys will be fixed and replay could be a possibility. Zebedee protects against this by generating a unique session key for each connection. Following that, the final part of the connection setup also involves a challenge-response exchange that verifies that the system at the other end of the connection really knows the shared secret key and is not just parrotting back previously recorded data.
In addition, Zebedee uses Blowfish encryption in "cipher feedback" mode which means that decryption of any part of the data depends upon successful decryption of all the data packets that have gone before it. The challenge-response exchange "salts" the data-stream so even if the protocol being tunnelled is determined a "known plain-text" attack is made more difficult.
A poorly-chosen key can compromise even the strongest encryption mechanism. When generating keys Zebedee attempts to gather as much hard-to-guess state data as possible and then "stir" it using the SHA hashing algorithm. On modern UNIX systems this generation process should give pretty good keys.
On Windows the available state data is somewhat more predictable, particularly if an attacker has access to the system. Having said that, it should be quite acceptable for most purposes. The comments in the code explain this in more detail if you are interested.
If you are unhappy with the key generation mechanisms then you should call out to an external key generation program using the keygencommand option in a configuration file. Suggestions for improving the built-in capabilities will also be gratefully received!
By default, if you do not specify any target ports either in a target specification or with a redirect keyword a Zebedee server will accept requests to make connections to any port. This is almost certainly not what you want in a production environment.
A "denial of service" attack is one where a malicious user does not attempt to capture secret information but instead tries to render a service unavailable or unusable. In common with many network service, Zebedee is somewhat vulnerable to such attacks. If this is a particular concern to you then you may wish to employ the readtimeout keyword in order to reduce the susceptibility to this kind of attack.
Although Zebedee should work "out of the box" you might encounter some problems. These are most likely during connection setup --- once that has been accomplished the data transfer generally goes smoothly. The eaisest way to see what is happening during the setup process is to use the -v option. You will usually want to combine this with the -d and -D options to stop Zebedee from the terminal and to force it to handle only a single connection at a time. So, for example, you might use the following command to start up a server:
zebedee -dD -v 3 -s
Setting the logging level to 3 should show you the main exchanges during connection setup. If you believe there is a problem after this then levels 4 and 5 will show you what message traffic is being exchanged.
In the Zebedee distribution there are a number of example configuration files. The following sections describe how they can be used as well as how to use Zebedee to tunnel some specific protocols.
There is an example server configuration file (server.zbd) shipped with the Zebedee distribution. This shows most of the common options.
# # Sample Zebedee server configuration file # # This shows the use of many, but not all, of the configuration file # options available for use by a server. # verbosity 2 # Slightly more than basic messages # Comment out the following line once you have read the comments # in this file and enabled or disabled the appropriate options! message "DEFAULT CONFIGURATION FILE -- EDIT BEFORE USE" detached false # You will probably want this 'true' for normal # use but I want to make sure that you see the # preceding message if you haven't edited this. server true # Yes, it's a server! ipmode both # Operate in mixed TCP/UDP mode compression zlib:9 # Allow maximum zlib compression keylength 256 # Allow keys up to 256 bits keylifetime 36000 # Shared keys last 10 hours maxbufsize 16383 # Allow maximum possible buffer size # Uncomment the following line to log messages to a local file. # # logfile './server.log' # # Or to log to the system logging facility uncomment this: # # logfile SYSLOG keygenlevel 2 # Generate maximum strength private keys # Uncomment the following line if you want to use a fixed private # key stored in a static file. The file should contain a line of # the form "privatekey hexadecimal-key-string". This file should # be readable by the user running Zebedee but no-one else. # # include './server.key' # To validate the identity of clients use a line something like # the following: # # checkidfile './clients.id' # The "redirect" expression can be use to set the default ports # allowed when a target specification consists of a hostname but # no other ports. The "redirect none" statement prohibits # tunnelling anywhere by default. redirect none # Set up allowed targets. Note that there are NO targets allowed # by this file by default. You must explicitly edit it to enable # them. # The following are good for testing purposes. Either TCP or UDP # are allowed. # # target localhost:daytime,echo,chargen # Basic interactive services, TCP only. # # target localhost:telnet/tcp,ftp/tcp # VNC traffic -- usually you will only need a subset of this # range, perhaps 5900 or 5901. # # target localhost:5900-5999/tcp # X Window System -- again, usually you will only need # a subset of this range. # # target localhost:6000-6010/tcp # Here is an example of specifying targets using a subnet. In # this case allowing tunnels to be established to VNC servers # on the 10.1.1.xx subnet. # # target 10.1.1.0/24:5900/tcp # The following line ensures that the default target host # is the local machine. The last named host becomes the # default so leaving this here ensures that "localhost" is, # the default unless overridden on the command line. target localhost
To test the identity checking facilities you can uncomment the checkidfile line and then use one of the supplied client1.key or client2.key files on the client side.
One of the reasons behind writing Zebedee was to use it over dial-up lines with VNC. VNC is a free system to provide remote display capabilities using a "remote frame-buffer" concept. You can use it to display Windows desktops remotely or, with an "Xvnc" server to access an "X desktop" from any VNC client machine, or even a Java-enabled browser! See http://www.uk.research.att.com/vnc/ for more details.
The supplied sample server configuration file server.zbd has sample target statements (commented out by default) that are configured to allow redirection of ports 5900-5999 which will allow tunnelling of VNC sessions. This file can be used on both UNIX and Windows but note that on Windows you must set the "AllowLoopback" flag in the registry in order for tunnelling to work. Saving the following snippet (without any leading spaces) in file a and then importing it into regedit will do the trick:
REGEDIT4 [HKEY_LOCAL_MACHINE\SOFTWARE\ORL\WinVNC3] "AllowLoopback"=dword:00000001 [HKEY_LOCAL_MACHINE\SOFTWARE\ORL\WinVNC3\Default] "AllowLoopback"=dword:00000001
You will find a file with these contents in the Zebedee distribution by the name vncloopback.reg. Having set these registry entries then the file vncviewer.zbd can be used to invoke a VNC viewer tunnelled to the host named on the command line. Here are the contents of the file vncviewer.zbd:
# # Zebedee configuration file to start up a tunnelled VNC session # # Usage: zebedee -f vncviewer.zbd remote-host:vnc-port # verbosity 1 # Basic messages only server false # It's a client detached true # Detach from terminal message "Starting VNC viewer" # On Windows systems you might use the following: command '"c:\Program Files\ORL\VNC\vncviewer.exe" localhost:%d' # On UNIX systems you might use the following: # command 'vncviewer localhost:%d' compression 6 # Request normal Zlib compression
So using this file as follows:
zebedee -f vncviewer.zbd somehost:5901
will start a VNC viewer tunnelled to the VNC server on somehost port 5901 (the server you would usually refer to in VNC-parlance as "somehost:1").
VNC also supports a Java viewer. If the server is running on port 59xx then the viewer can be downloaded via port 58xx. However, it appears that the Java viewer communicates the main VNC port number to the client. So, to tunnel traffic when using the Java viewer you must make sure that the local and remote ports use the same numbers. So, for example, to tunnel traffic to a VNC server using port 5901 you should do something like:
This will be problematic if you already have a VNC server running locally on port 5901, but you can usually arrange local and remote VNC servers so that there is no clash.
There is one last point worth mentioning. If you are using compression with VNC it is worth experimenting a bit with the VNC protocol encoding. I have found that "raw" encoding often compresses best and sometimes gives better performance with Zebedee over slow links. But, as they say, your mileage may vary!
The X Window System uses ports in the range 6000 onwards.
Let's assume that your local machine called xlocal is running an X server on port 6000. This would be the port normally used by the display known as xlocal:0. You now want to send a secure xterm session back to your local display from a machine called xremote. To do this you might run the following command on xlocal:
zebedee -s localhost:6000
Then on xremote you could run:
This means that if the DISPLAY environment variable on xremote is set to
localhost:1 then X traffic will end up on xlocal. So, for example, to send a secured xterm session from xremote to xterm you would run a command like this on xremote:
xterm -display localhost:1
Note that in order for this to work correctly you must also add an entry for localhost to the access control list for the X server on xlocal. You can do this by running the following command on xlocal:
Zebedee can be used to secure or just compress all traffic to and from a Web server. So, for example, if a Web server is running on the machine webhost on port 80 and it is also running a Zebedee server then the command:
will set up a tunnel via port 8000 on the client host. Now any URLs that previously were addressed via webhost, for example:
can now be accessed securely as follows:
You could redirect all HTTP traffic via the secure tunnel by setting "
localhost:8000" as your proxy. Be careful, however, only to set this as the proxy for HTTP connections --- other protocols (including Secure HTTP) should be directed elsewhere. It is also possible to configure most browsers to use different proxies for different domains and so secure connections selectively. Consult your browser's documentation for details on how to do this.
It is possible to protect the FTP control connection (over which the username and password are sent) for many FTP servers using Zebedee "out of the box" by following the instructions below. It may also be possible to protect the control connection for other servers and even "passive-mode" data connections by using Zebedee in conjunction with one of the techniques described below.
The simplest approach, which will protect the control connection and which works with some FTP servers, is to run the Zebedee server as follows:
zebedee -s ftpserverhost:ftp
Note that even if you are running Zebedee on the same machine as the FTP server you should explictly name it on the command line (or using the target keyword). Do not refer to it as localhost. On the client system you could then run Zebedee as follows to set up a tunnel via port 10000:
To connect to the FTP server you would then use a command like:
ftp clienthost 10000
Again, use the local client host name not, localhost. If your FTP client does not support specifying the port on the command line, as is the case with the standard Windows FTP client program, you may be able to use the command "
open clienthost 10000" from within the program. If you are not running an FTP server on the client machine you could also try running Zebedee as:
and then just invoking the FTP client program as:
The approach just described will work for FTP servers that do not check that the FTP control and data connections appear to come from the same source. However, some servers such as the widely-used wu-ftpd are more strict about this --- for good security reasons. If you can apparently establish a connection to the server but directory listing and file retrievals fail or hang then it is likely that your server is one of the strict ones.
If you find yourself in this situation then a good approach (suggested by Magnus Wedburg) is to investigate your FTP server's support for operating with firewalls and Network Address Translation (NAT). Many modern servers, including wu-ftpd, allow you to specify the address that a server will report for itself in FTP requests. They will also allow you to specify a range of ports which will be used for "passive mode" connections. If you can specify these two values you should be able to use Zebedee to tunnel both control traffic and also data traffic for passive connections. Support for passive mode depends upon the particular FTP client being used. Netscape Navigator and the Windows program
WS_FTP are examples of clients able to do this.
Assuming that you have the capability to specify the server response address and range of ports you can the use Zebedee as follows. First, set the response address to the
localhost address, that is,
127.0.0.1. Then select a range of ports to be used for tunnelling passive-mode data connections. The size of the range will limit the number of simultaneous connections that can be handled. In this case we will chose 30000-30010. Now, on the FTP server run:
zebedee -s localhost:ftp,30000-30010
Then on the client run:
The value of 2121, for the FTP control connection, could be any other convenient port. The passive port range must, however, be the same as that on the server. To access the server with both control and data connections secured using Netscape you would then supply a URL of the form:
where username is your user-name on the FTP server host.
If you can't configure the target FTP server as described above then there is one more method that you can try. The Zebedee distribution contains an "FTP gateway" script called ftpgw.tcl. This is a program, written using the freely-available Tcl scripting language (see http://tcl.activestate.com) that intercepts FTP requests and re-writes them so that a server is shielded from the presence of Zebedee. You should run this on the same system as the Zebedee server. Assuming that the FTP server is also running on the same system you can just run this as:
This will start the gateway listening on port 2121. Obviously, in real usage you will probably want to start this in the background. You then start the Zebedee server as:
zebedee -s localhost:2121
Note that in this case you do specify the local host as the target. On the client side you can now run:
ftp clienthost 2121
You must still, however, use the client host name here.
This configuration will allow you to tunnel the FTP control connection but will not affect any data connections. Using ftpgw.tcl it is, however, also possible to secure the passive-mode data channels in a similar manner to that described above.
To secure passive-mode data connections you must choose a range of ports on the server that will be used for data connections. In this example we will again use 30000 to 30010. You then start ftpgw.tcl with the -p option to specify this port range:
tclsh ftpgw.tcl -p 30000-30100
The Zebedee server would then be started as:
zebedee -s localhost:2121,30000-30100
and the client as
To access the server with both control and data connections secured using Netscape you would then supply a URL, identical to that shown above, of the form:
This section outlines the main user-visible changes since the previous "stable" release, 2.4.1. Full details, including bug fixes and other non-visible enhancements, are in the
CHANGES.txt file in the Zebedee distribution.
Backwards compatibility with Zebedee 1.x versions of the protocol (which is now more than 3 years old) has been dropped. Compatibility is maintained for releases 2.0.0 and upward.
New message integrity checking keywords (checksumlevel and minchecksumlevel) have been added. These give assurance that messages have not been tampered with in transit. Also the keywords dropunknownprotocol and lockprotocol help enforce the use of these features, if required. These are all derived from patches submitted by, Henrick Lund. Great work Henrick!
Added the ability to hand the peer address, target address and target port to key generation commands (add a "
+" to the end of the command to get three extra arguments provided). See keygencommand and sharedkeygencommand for further details.
Added httpproxyauth" -- thanks to James CE Johnson.
Added runasuser|/item_runasuser> (and the -N option) -- thanks to Thomas Melzer.
The target specification has been extended to allow per-target client identity and address checking. The identity checking was originally submitted by Alain Turbide and address checking by Henrik Lund (again!)
The acceptconnecttimeout connectattempts, serverconnecttimeout and targetconnecttimeout keywords have been added to significantly improve the "reverse-mode" operation.
Add maxconnections to alleviate potential denial of service attacks.
The following information can also be found in the file LICENCE.txt in the Zebedee distribution.
Copyright (c) 1999-2003 by Neil Winton. All Rights Reserved. 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.
A copy of the GNU General Public License can be found in the file GPL2.txt.
You may obtain the latest copy of Zebedee, including full source code from http://www.winton.org.uk/zebedee/ and other enquiries about Zebedee can be e-mailed to the author at firstname.lastname@example.org
Zebedee would not have been possible without the use of a large amount of freely-available software to do all the really hard stuff. I gratefully acknowledge the contributions made by the authors of the following software packages.
Zebedee uses the "Blowfish" encryption algorithm devised by Bruce Schneier. For more information on Blowfish see http://www.counterpane.com/blowfish.html . The implementation used is by Eric Young and is covered by the following copyright:
Copyright (C) 1995-1997 Eric Young (email@example.com) All rights reserved. This package is an Blowfish implementation written by Eric Young (firstname.lastname@example.org). This library is free for commercial and non-commercial use as long as the following conditions are aheared to. The following conditions apply to all code found in this distribution. Copyright remains Eric Young's, and as such any Copyright notices in the code are not to be removed. Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met: 1. Redistributions of source code must retain the copyright notice, this list of conditions and the following disclaimer. 2. 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. 3. All advertising materials mentioning features or use of this software must display the following acknowledgement: This product includes software developed by Eric Young (email@example.com) THIS SOFTWARE IS PROVIDED BY ERIC YOUNG ``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 AUTHOR 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. The license and distribution terms for any publically available version or derivative of this code cannot be changed. i.e. this code cannot simply be copied and put under another distrubution license [including the GNU Public License.] The reason behind this being stated in this direct manner is past experience in code simply being copied and the attribution removed from it and then being distributed as part of other packages. This implementation was a non-trivial and unpaid effort.
Zebedee uses the zlib compression library by Jean-loup Gailly and Mark Adler. It is covered by the following copyright notice:
(C) 1995-1998 Jean-loup Gailly and Mark Adler This software is provided 'as-is', without any express or implied warranty. In no event will the authors be held liable for any damages arising from the use of this software. Permission is granted to anyone to use this software for any purpose, including commercial applications, and to alter it and redistribute it freely, subject to the following restrictions: 1. The origin of this software must not be misrepresented; you must not claim that you wrote the original software. If you use this software in a product, an acknowledgment in the product documentation would be appreciated but is not required. 2. Altered source versions must be plainly marked as such, and must not be misrepresented as being the original software. 3. This notice may not be removed or altered from any source distribution. Jean-loup Gailly Mark Adler firstname.lastname@example.org email@example.com
Zebedee may use the bzip2 compression library by Julian Seward which is covered by the following licence:
This program, "bzip2" and associated library "libbzip2", are copyright (C) 1996-1999 Julian R Seward. All rights reserved. Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met: 1. Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer. 2. The origin of this software must not be misrepresented; you must not claim that you wrote the original software. If you use this software in a product, an acknowledgment in the product documentation would be appreciated but is not required. 3. Altered source versions must be plainly marked as such, and must not be misrepresented as being the original software. 4. The name of the author may not be used to endorse or promote products derived from this software without specific prior written permission. THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``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 AUTHOR 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. Julian Seward, Cambridge, UK. firstname.lastname@example.org bzip2/libbzip2 version 0.9.5 of 24 May 1999
By default Zebedee is built using an aribtrary precision integer arithmetic library derived from the sources to
mirrordir-0.10.49 which in turn derived this from the Python sources. The copyright is as follows:
huge-number.c: arbitrary precision integer library from Python sources This has nothing to do with cryptography. Copyright (C) 1998 Paul Sheer 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., 675 Mass Ave, Cambridge, MA 02139, USA. This file was taken from the Python source for `long' type integers. I have changed it to compile independently of the Python source, and added the optimisation that GNU C can use 31 bit digits instead of Python's 15 bit. You can download the original from www.python.org. This file bears little resemblance to the original though - paul Copyright 1991-1995 by Stichting Mathematisch Centrum, Amsterdam, The Netherlands. All Rights Reserved Permission to use, copy, modify, and distribute this software and its documentation for any purpose and without fee is hereby granted, provided that the above copyright notice appear in all copies and that both that copyright notice and this permission notice appear in supporting documentation, and that the names of Stichting Mathematisch Centrum or CWI or Corporation for National Research Initiatives or CNRI not be used in advertising or publicity pertaining to distribution of the software without specific, written prior permission. While CWI is the initial source for this software, a modified version is made available by the Corporation for National Research Initiatives (CNRI) at the Internet address ftp://ftp.python.org. STICHTING MATHEMATISCH CENTRUM AND CNRI DISCLAIM ALL WARRANTIES WITH REGARD TO THIS SOFTWARE, INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS, IN NO EVENT SHALL STICHTING MATHEMATISCH CENTRUM OR CNRI BE LIABLE FOR ANY SPECIAL, INDIRECT OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
Zebedee uses the Secure Hash Algorith (SHA) the code for which was derived from Uwe Hollerbach's SHA module for perl. The code contains the following statement:
NIST Secure Hash Algorithm heavily modified by Uwe Hollerbach <email@example.com edu> from Peter C. Gutmann's implementation as found in Applied Cryptography by Bruce Schneier This code is in the public domain
Under Windows, Zebedee uses an implementation of the getopt function covered by the following copyright:
Copyright (c) 1987, 1993, 1994 The Regents of the University of California. All rights reserved. Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met: 1. Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer. 2. 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. 3. All advertising materials mentioning features or use of this software must display the following acknowledgement: This product includes software developed by the University of California, Berkeley and its contributors. 4. Neither the name of the University 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 REGENTS 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 REGENTS 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.
Special thanks go to those people who have taken the trouble to give me feedback and suggestions for improvement!
$Id: zebedee.pod,v 1.31 2005/09/02 22:10:41 ndwinton Exp $