sshproxy

README

sshproxy

This is a PoC ssh proxy written in Go. It is meant as a toy proxy to play around with and help me figure out how exactly the ssh protocol works.

It is meant to be as simple as possible and the only significant dependency is the x/crypto/ssh package. I've seen some other implementations, but these have been rather complex with a heavy reliance on complex closures.

Except for the obvious lack of security (it accepts any public key) the code should be reasonably ready to be plopped into production.

How it works

It binds to port 4222. On a successful authentication it will ssh into the destination (localhost:3222) and then proxy the connection.

docker image.

Alternative approach to proxying

This approach includes rather protocol-intensive proxying. I'm not familiar enough with SSH to know whether this could be done simpler, perhaps by copying the decrypted bytes coming from the one connection to the next.

Notable ssh proxies in Go

Other proxies and ssh implementations to look at:

• https://github.com/appleboy/easyssh-proxy
• https://github.com/blacknon/go-sshlib
• https://github.com/tsurubee/sshr
• https://github.com/gliderlabs/ssh

How to build

See the Makefile. It should contain targets for all operations you'll need.

What is missing?

At the moment I've not tried sftp. I don't need it, I expect it would work but it does perhaps need changed to sshd_config to allow the sftp subsystem to be enabled.

Hacks and uglyness.

When the channel of requests is closed the proxyRequest function will sleep for 10ms. This is to make sure that stdout and stderr gets copied to the client. Suggestions for how to do this cleanly are welcome.