go-tunnel - Robust Quic/TLS Tunnel (Stunnel replacement)
What is it?
A supercharged Stunnel replacement written in golang. is in a sense a proxy enabling addition of network-encryption to existing clients without any source code changes.
- TLS 1.3 for client and server mode (TLS Connect or TLS Listen)
- Quic client and server mode (Quic listen or Quic connect)
- Optional SOCKS for connecting endpoint (SOCKS server)
- Optional TLS client certificate (for Quic/TLS Connect)
- SNI on the listening Quic/TLS server
- Ratelimits - global and per-IP
- Proxy-Protocol v1 support when connecting to downstream servers
- YAML Configuration file
- Access Control on per IP or subnet basis (allow/deny combination)
- Strong ciphers and curves preferred on both client & server
- Comes with end-to-end tests covering variety of scenarios
Note that TLS private keys need to be unencrypted; we don't support password protected private keys yet. The main reason for this is that when
gotun is daemonized, it may not be possible to obtain the password in an interactive manner. Additionally, for SNI support, it may be impossible to ask for interactive password in the middle of a client connection setup.
Lets assume you have a public server on
proxy.example.com listening on Quic/UDP supporting SOCKS protocol for connecting to outbound destinations. For security reasons, you want to limit access to only clients that are TLS authenticated (TLS client certs).
Lets also assume that you have a laptop that wants to connect to the SOCKS server efficiently.
Using two instances of
gotun, you can accomplish this:
Local gotun instance on your laptop configured to accept TCP and connect using Quic to the external server
Server gotun instance on the external host configured to accept authenticated Quic connections and proxy via SOCKS.
Configure your laptop browser to use the "local" SOCKS server.
Using Quic to connect the two
gotun instances reduces the TCP/TLS overhead of every socks connection. And, TLS client certs enables strong authentication on the external server.
The picture below explains the connectivity:
In the setup above, the laptop browser clients will treat
127.0.0.1:1080 as their "real" SOCKS server. Behind the scenes,
gotun will tunnel the packets via Quic to a remote endpoint where a second
gotun instance will unbundle the SOCKS protocol and connect to the final destination.
The config file shown above actually demonstrates a really secure tunnel where the server and client both use certificates to authenticate each other.
Assuming the config on "Gotunnel Laptop" is in file
client.conf, and the config on "Gotunnel Server" is in
server.conf, to run the above example, on host "Gotunnel-A":
And, on the public server:
-d flag for
gotun runs it in debug mode - where the logs are sent to STDOUT. It's not recommended to run a production server in debug mode (too many log messages).
You need a reasonably new Golang toolchain (1.14+). And the
go executable needs to be in your path. Then run:
Make essentially runs:
build will build the binary
gotun and places it in TARGET specific directory. e.g., for linux-amd64, the binaries will be in
./bin/linux-amd64; and OS X, it will be in
./bin/darwin-amd64 and so on.
You can cross-compile 'go-tun' by passing appropriate architecture names to the script. e.g., to build on host OS X for openbsd-amd64:
You can build a statically linked executable (with no other runtime dependency):
The script also has other options. To see them::
gotun takes a YAML config file as its sole command line argument. The server does not fork itself into the background. If you need that capability, explore your platform's init toolchain (e.g.,
The server can run in debug mode; e.g., on Linux x86_64:
./bin/linux-amd64/gotun -d etc/gotun.conf
In debug mode, the logs are sent to STDOUT and the debug level is set to DEBUG (i.e., verbose).
In the absence of the
-d flag, the default log level is INFO or whatever is set in the config file.
The config file is a YAML v2 document. A complete, self-explanatory example is below:
# Log file; can be one of: # - Absolute path # - SYSLOG # - STDOUT # - STDERR log: STDOUT #log: STDOUT # Logging level - "DEBUG", "INFO", "WARN", "ERROR" loglevel: DEBUG # config dir - where all non-absolute file references below will # apply. config-dir: /etc/gotun # Listeners listen: # Listen plain text - address: 127.0.0.1:9090 allow: [127.0.0.1/8, 184.108.40.206/24, 220.127.116.11/24] deny:  timeout: connect: 5 read: 2 write: 2 # limit to N reqs/sec globally ratelimit: global: 2000 per-host: 30 cache-size: 10000 # Connect via TLS connect: address: host.name:443 bind: my.ip.address tls: cert: /path/to/crt key: /path/to/key # path to CA bundle that can verify the server certificate. # This can be a file or a directory. ca: /path/to/ca.crt # if address is a name, then servername is populated from it. # else, if it is an IP address, it must be set below. # Not setting it => no verification (InsecureSkipVerify = true) # servername: a.example.com # Listen using TLS with SNI - address: 127.0.0.1:9443 allow: [127.0.0.1/8, 18.104.22.168/24, 22.214.171.124/24] deny:  timeout: connect: 5 read: 2 write: 2 tls: sni: /path/to/cert/dir # clientcert can be "required" or "optional" or "blank" or absent. # if it is required/optional, then clientca must be set to the list of # CAs that can verify a presented client cert. client-cert: required client-ca: /path/to/clientca.crt # plain connect but use proxy-protocol v1 when speaking # downstream connect: address: 126.96.36.199:80 proxyprotocol: v1 # Listen on Quic + client auth and connect to SOCKS - address: 127.0.0.1:8443 tls: quic: true cert: /path/to/crt key: /path/to/key # path to CA bundle that can verify the server certificate. # This can be a file or a directory. ca: /path/to/ca.crt client-cert: required client-ca: /path/to/clientca.crt connect: address: SOCKS
etc/ directory has example configurations for running Quic+SOCKS on a public server and a local laptop.
SNI is exposed via domain specific certs & keys in the
tls.certdir config block. SNI is enabled by setting
tls.sni config element to
true; and each hostname that is requested via SNI needs a cert and key file with the file prefix of hostname. e.g., if the client is looking for hostname "blog.mydomain.com" via SNI, then
gotun will look for
blog.mydomain.com.key in the directory identified by
tls.certdir. The config file above has an example for SNI configured on listen address
Generating Local Certificates
If you want client authentication and don't want the hassle of using openssl or a commercial CA for obtaining the certs, you can use certik to create an easy, opinionated local CA infrastucture. Assuming you are on a linux-amd64 platform:
$ git clone https://github.com/opencoff/certik $ cd certik $ ./build -s $ ./bin/linux-amd64/certik ca.db init "client CA" $ ./bin/linux-amd64/certik ca.db user [email protected] $ ./bin/linux-amd64/certik ca.db export -o ca --ca $ ./bin/linux-amd64/certik ca.db export -o username [email protected]
Now, you have
ca.crt as the CA root of trust for the Quic server to validate client certs. And, the client cert/key for
[email protected] is in
You can copy and use
ca.crt and user's cert/key to
gotun config directory and refer to it in the config file under "client-ca" and "tls.cert", "tls.key" respectively.
gotun tries to be safe by default:
- Opinionated TLS 1.3 configuration
- All config file references are checked for safety: e.g., any TLS certs/keys are verified to have sane permissions (NOT group/world writable)
Using iperf3 on two debian-linux (amd64) hosts connected via Gigabit Ethernet and
gotun running on either end, the performance looks like so:
$ iperf3 -V -c 127.0.0.1 -p 9000 iperf 3.1.3 Linux ungoliant 4.15.0-2-amd64 #1 SMP Debian 4.15.11-1 (2018-03-20) x86_64 Time: Sat, 28 Apr 2018 21:18:46 GMT Connecting to host 127.0.0.1, port 9000 Cookie: ungoliant.1524950326.966562.77625193 TCP MSS: 21888 (default) [ 4] local 127.0.0.1 port 35444 connected to 127.0.0.1 port 9000 Starting Test: protocol: TCP, 1 streams, 131072 byte blocks, omitting 0 seconds, 10 second test [ ID] Interval Transfer Bandwidth Retr Cwnd [ 4] 0.00-1.00 sec 54.5 MBytes 457 Mbits/sec 0 2.50 MBytes [ 4] 1.00-2.00 sec 45.7 MBytes 383 Mbits/sec 0 2.50 MBytes [ 4] 2.00-3.00 sec 46.2 MBytes 388 Mbits/sec 0 2.50 MBytes [ 4] 3.00-4.00 sec 46.5 MBytes 390 Mbits/sec 0 2.50 MBytes [ 4] 4.00-5.00 sec 46.6 MBytes 391 Mbits/sec 0 2.50 MBytes [ 4] 5.00-6.00 sec 46.2 MBytes 388 Mbits/sec 0 2.50 MBytes [ 4] 6.00-7.00 sec 47.0 MBytes 394 Mbits/sec 0 2.50 MBytes [ 4] 7.00-8.00 sec 47.7 MBytes 400 Mbits/sec 0 2.50 MBytes [ 4] 8.00-9.00 sec 47.5 MBytes 398 Mbits/sec 0 2.50 MBytes [ 4] 9.00-10.00 sec 46.7 MBytes 392 Mbits/sec 0 2.50 MBytes - - - - - - - - - - - - - - - - - - - - - - - - - Test Complete. Summary Results: [ ID] Interval Transfer Bandwidth Retr [ 4] 0.00-10.00 sec 475 MBytes 398 Mbits/sec 0 sender [ 4] 0.00-10.00 sec 464 MBytes 389 Mbits/sec receiver CPU Utilization: local/sender 1.8% (0.0%u/1.7%s), remote/receiver 9.0% (0.6%u/8.4%s)
Access Control Rules
Go-tunnel implements a flexible ACL by combination of allow/deny rules. The rules are evaluated in the following order:
- If explicitly denied, then host is blocked
- If allow list is empty, then host is allowed
- If allow list is non-empty & host is in allow-list, then host is allowed
- Explicit denial takes precedence over explicit allow
- Default (fall through) policy is to deny
Example of allow/deny combinations
- Allow all:
allow:  deny: 
- Only allow specific subnets and deny everyone else:
allow: [ 192.168.55.0/24, 172.16.10.0/24, 127.0.0.1/8 ] deny: 
- Allow all except selected subnets:
allow:  deny: [ 192.168.80.0/24, 172.16.5.0/24 ]
- Expliclty block certain hosts and explicitly allow certain subnets and block everyone else:
allow: [ 192.168.55.0/24, 172.16.10.0/24, 127.0.0.1/8 ] deny: [ 192.168.1.1/32, 192.168.80.0/24, 172.16.5.0/24 ]
If you are a developer, the notes here will be useful for you:
The code uses go modules; so, you'll need a reasonably new go toolchain (1.10+)
The go-tunnel code is in
- server.go: Implements TCP/TLS and Quic servers; also implements the SOCKS server protocol
- conf.go: YAML configuration file parser
- quicdial.go: Dial outbound connections via Quic + streams
- tcpdial.go: Dial outbound connections via TCP
- safety.go: Safely open files/dirs referenced in config file
Tests: running tests:
go test -v ./srcSome of the tests/helpers:
- mocked_test.go: Mock servers and clients
- tcp_test.go: Tests for TCP/TLS to TCP/TLS
- quic_test.go: Tests for TCP/TLS to Quic and vice versa
- socks_test.go: Tests for socks (includes a test for the example configuration above)
- utils_test.go: test helpers (e.g.,
build- a a master shell script to build the daemons; it does two very important things:
- Puts the binary in an OS/Arch specific directory
- Injects a git version-tag into the final binary ("linker resolved symbol")
This script can be reused for other go projects.
Example config files is in the