NAME

gsocket —

connect like there is no firewall. Securely.

SYNOPSIS

gsocket [-qT] [-s secret] [-k keyfile] [-p port] [program] [args ...]

DESCRIPTION

The gsocket tool can be used to enable a program to communicate through a firewall in situations where it would not be possible to establish a direct connection to another host/workstation (NATed/firewalled). The typical scenario is two workstations that are on separate private networks and behind separate firewalls. The gsocket tool hijacks the network library functions (such as connect() and accept()) of the program and encrypts and redirects the traffic through the Global Socket Relay Network (GSRN).

Neither workstation needs to open a port in their firewall nor accept incoming TCP connections.

The connection is end-2-end encrypted using SRP (RFC 5054) with AES-256 and a 4096 Prime. The GSRN sees only the encrypted traffic.

Common uses include:

ssh from one workstation to another
OpenVPN between two workstations
netcat between two workstations
and much, much more.

...while both workstations are behind NAT and firewalled.

Abandon the thought of IP addresses and port numbers: Two programs should be able to communicate with each other as long as they know the same secret (rather than each other´s IP address and port number). The gsocket tools establishes such a connection regardless and independent of the local IP address or geographical location. It does so by analyzing the program and replacing the IP Layer with its own transport through GSRN. The connection is end-2-end encrypted. The GSRN sees only the encrypted traffic.

The typical scenario is a client/server arrangement such as ssh and sshd: Connections by ssh to any hostname ending in ´.gsocket´ are redirected (through the GSRN) to the (firewalled) sshd server.

The redirection is done per program (and limited to that program only). The gsocket tool does not change the routing table and does not change the NAT nor the firewall settings. It does not require superuser privileges either.

OPTIONS

-s secret: A secret chosen by the user. Both ends need to use the same secret to connect.
-k file: A file containing the secret.
-g: Generate a secure random secret and output it to standard output.
-q: Quiet mode. Do not output any warnings or errors.
-T: Use TOR. The gsocket tool will connect through TOR to the GSRN. This requires TOR to be installed and running.
-p port: TCP port range of listening ports to redirect [default=all].

Connections to any hostname ending in ´*.gsocket´ or to the IP Address ´127.31.33.7´ are redirected through the GSRN.

Connections to any hostname ending in ´*.thc´ or to the IP Address ´127.31.33.8´ are first redirected through TOR and then through the GSRN.

EXAMPLES

Example 1 - OpenSSH between two firewalled workstations:

Server:

$ gsocket -s MySecret
  /usr/sbin/sshd

Client:

$ gsocket -s MySecret ssh
  xaitax@gsocket

Example 2 - netcat between two firewalled workstations:

Server:

$ gsocket -s MySecret nc -lp
  31337

Client:

$ gsocket -s MySecret nc gsocket
  31337

Example 3 - OpenVPN between two firewalled workstations:

Server:

$ gsocket -s MySecret openvpn --dev
  tun1 --proto tcp-server --ifconfig 10.9.8.1 10.9.8.2

Client:

$ gsocket -s MySecret openvpn --dev
  tun1 --proto tcp-client --ifconfig 10.9.8.2 10.9.8.1 --remote
  gsocket

Example 4 - IRCD between two firewalled workstations:

Server:

$ gsocket -s MySecret inspircd
  --nolog --nofork

Client:

$ gsocket -s MySecret irssi -c
  gsocket

Example 5 - Socat between two firewalled workstations:

Server:

$ gsocket -s MySecret socat -
  TCP_LISTEN:31337

Client:

$ gsocket -s MySecret socat -
  TCP:gsocket:31337

SYSTEMCTL INSTALLATION

It is possible to make any service/daemon accessible through any firewall. The service is then only acessible through the GSRN and only if the client knows the secret. No port or service is exposed to the public Internet and the existence of the service remains hidden. This example makes openssh-server (sshd) accessible through the GSRN. Nobody, not even the GSRN operators, have access to the port, daemon or service (they do not know the secret). The new service coexists with the existing openssh-server and does not interfere with the existing openssh-server.

1. Copy /etc/systemd/system/sshd to /etc/systemd/system/gs-sshd

2. Edit /etc/systemd/system/gs-sshd and change this line:

ExecStart=/usr/sbin/sshd -D
  $SSHD_OPTS

ExecStart=gsocket -s MySecret
  /usr/sbin/sshd -D $SSHD_OPTS

3. Start the newly created service

# systemctl start
  gs-sshd

4. Check the status

# systemctl status
  gs-sshd

5. Connect from any other host to the newly created (hidden) openssh-server:

$ gsocket -s MySecret ssh
  user@gsocket

ENVIRONMENT

The following environment variables can be set to control the behavior of gsocket

GSOCKET_SOCKS_IP

Specify the IP address of the TOR
  server (or any other SOCKS server). Default is 127.0.0.1.

GSOCKET_SOCKS_PORT

The port number of the TOR server (or
  any other SOCKS server). Default is 9050.

GSOCKET_ARGS

A string containing additional
  command line parameters. First the normal command line parameters are
  processed and then the command line parameters from GSOCKET_ARGS.

SECURITY

Passing the password as command line parameter is not secure. Consider using the -k option or GSOCKET_ARGS or enter the password when prompted:

$ gsocket -k
  <file>

$ export GSOCKET_ARGS="-s
  MySecret"

$ gs

1. The security is end-2-end. This means from user-2-user (and not just to the GSRN). The GSRN relays only (encrypted) data to and from the users.

2. The session is 256 bit and ephemeral. It is freshly generated for every session and generated randomly (and is not based on the password). It uses OpenSSL´s SRP with AES-256 and a 4096 Prime.

3. The password can be ´weak´ without weakening the security of the session. A brute force attack against a weak password requires a new TCP connection for every guess.

4. Do not use stupid passwords like ´password123´. Malice might pick the same (stupid) password by chance and connect. If in doubt use gs-netcat -g to generate a strong one. Alice´s and Bob´s password should at least be strong enough so that Malice can not guess it by chance while Alice is waiting for Bob to connect.

5. If Alice shares the same password with Bob and Charlie and either one of them connects then Alice can not tell if it is Bob or Charlie who connected.

6. Assume Alice shares the same password with Bob and Malice. When Alice stops listening for a connection then Malice could start to listen for the connection instead. Bob (when opening a new connection) can not tell if he is connecting to Alice or to Malice. Use -a <token> if you worry about this. TL;DR: When sharing the same password with a group larger than 2 then it is assumed that everyone in that group plays nicely. Otherwise use SSH over the GS/TLS connection.

7. SRP has Perfect Forward Secrecy. This means that past sessions can not be decrypted even if the password becomes known.

NOTES

The latest version is available from https://github.com/hackerschoice/gsocket/.

BUGS

Efforts have been made to have gsocket "do the right thing" in all its various modes. If you believe that it is doing the wrong thing under whatever circumstances, please notify me (skyper@thc.org) and tell me how you think it should behave.