sshpiper

sshpiper 🖇

sshpiper is the reverse proxy for sshd. all protocols, including ssh, scp, port forwarding, running on top of ssh are supported.

Note: this is v1 version, checkout legacy v0 here

Overview and Terminology

• downstream: the client side, typicall ssh client
• upstream: the server side, typicall sshd server
• plugin: handles the routing from downstream to upstream. the plugin are also repsonsible for the mapping authentication methods to upstream. for exmaple, the downstream may use password as authentication method, but the upstream may receive public key authentication mapped by sshpiper.
• addtional chanllenge: some plugin will not do routing but add an additional challenges to ssh authentication to upstream. for example, the downstream may be asked for two factor authentication provided by the plugin.

+---------+                      +------------------+          +-----------------+
|         |                      |                  |          |                 |
|   Bob   +----ssh -l bob----+   |   sshpiper    +------------->   Bob' machine  |
|         |                  |   |               |  |          |                 |
+---------+                  |   |               |  |          +-----------------+
                             +---> pipe-by-name--+  |                             
+---------+                  |   |               |  |          +-----------------+
|         |                  |   |               |  |          |                 |
|  Alice  +----ssh -l alice--+   |               +------------->  Alice' machine |
|         |                      |                  |          |                 |
+---------+                      +------------------+          +-----------------+


 downstream                         sshpiper                        upstream                     

Quick start

Build

git clone https://github.com/tg123/sshpiper
cd sshpiper
git submodule update --init --recursive

mkdir out
go build -o out ./...

Run simple demo

start dummy sshd server

docker run -d -e USER_NAME=user -e USER_PASSWORD=pass -e PASSWORD_ACCESS=true -p 127.0.0.1:5522:2222 lscr.io/linuxserver/openssh-server

start sshpiperd with fixed plugin targetting the dummy sshd server

sudo ./out/sshpiperd ./out/fixed --target 127.0.0.1:5522

test ssh connection (password: pass)

ssh 127.0.0.1 -l user -p 2222

➕ math before login?

Here illustrates the example of addional challenge before the fixed plugin.

sudo ./out/sshpiperd --log-level=trace ./out/simplemath -- ./out/fixed --target 127.0.0.1:5522

Plugins

icons

• 🔀: routing plugin
• 🔒: addtional challenge plugin

Plugin list

• workingdir 🔀: /home-like directory to managed upstreams routing by sshpiped.
• workingdirbykey 🔀: same as workingdir but uses public key to route.
• yaml 🔀: config routing with a single yaml file.
• docker 🔀: pipe into docker containers.
• kubernetes 🔀: manage pipes via Kubernetes CRD.
• totp 🔒: TOTP 2FA plugin. compatible with all RFC6238 authenticator, for example: google authenticator, azure authenticator.
• azdevicecode 🔒: ask user to enter azure device code before login
• fixed 🔀: fixed targetting the dummy sshd server
• simplemath 🔒: ask for very simple math question before login, demo purpose

Screening recording

sshpiperd support recording the screen in typescript format (not the lang). The format is compatible with scriptreplay(1)

To use it, start sshpiperd with --typescript-log-dir loggingdir

Example:

```
ssh user_name@127.0.0.1 -p 2222
... do some commands
exit


$ cd loggingdir/user_name
$ ls *.timing *.typescript
1472847798.timing 1472847798.typescript

$ scriptreplay -t 1472847798.timing 1472847798.typescript # will replay the ssh session
```

Public key authentication when using sshpiper (Private key remapping)

During SSH publickey auth, RFC 4252 Section 7, ssh client sign session_id and some other data using private key into a signature sig. This is for server to verify that the connection is from the client not the man in the middle.

However, sshpiper actually holds two ssh connection, and it is doing what the man in the middle does. the two ssh connections' session_id will never be the same, because they are hash of the shared secret. RFC 4253 Section 7.2.

To support publickey auth, sshpiper routing plugin must provide a new private key for the upstream to sign the session_id. This new private key is called mapping key.

How this work

+------------+        +------------------------+                       
|            |        |                        |                       
|   client   |        |   sshpiper             |                       
|   PK_X     +-------->      |                 |                       
|            |        |      v                 |                       
|            |        |   Check Permission     |                       
+------------+        |      |                 |                       
                      |      |                 |                       
                      |      |                 |     +----------------+
                      |      v                 |     |                |
                      |   sign agian           |     |   server       |
                      |   using PK_Y  +-------------->   check PK_Y   |
                      |                        |     |                |
                      |                        |     |                |
                      +------------------------+     +----------------+

Migrating from v0

What's the major change in v1

• low level sshpiper api is fully redesigned to support more routing protocols.
• plugins system totally redesigned to be more flexible and extensible.
  • plugins are now sperated from main process and no longer a single big binary, this allow user to write their own plugins without touching sshpiperd code.
• grpc is first class now, the plugins are built on top of it

For plugins already in v1, you need change params to new params. However, not all plugins are migrated to v1 yet, they are being migrated gradually. you can still use the old plugins in v0 branch

Contributing

see CONTRIBUTING.md

License

MIT