SSH Piper

SSH Piper works as a proxy-like ware, and route connections by username, src ip , etc.

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


 Downstream                         SSH Piper                       Upstream                     

Install

go get -u github.com/tg123/sshpiper/sshpiperd

with pam module support

go get -u -tags pam github.com/tg123/sshpiper/sshpiperd

Docker image

Pull

docker pull farmer1992/sshpiperd

Run ❓ what is WORKING_DIR

docker run -d -p 2222:2222 \
  -v /etc/ssh/ssh_host_rsa_key:/etc/ssh/ssh_host_rsa_key \
  -v /YOUR_WORKING_DIR:/var/sshpiper \
  farmer1992/sshpiperd

Run with Additional Challenge

use env SSHPIPERD_CHALLENGER to specify which challenger to use

docker run -d -p 2222:2222 \
  -e SSHPIPERD_CHALLENGER=pam \
  -v /YOUR_PAM_CONFIG:/etc/pam.d/sshpiperd \
  -v /etc/ssh/ssh_host_rsa_key:/etc/ssh/ssh_host_rsa_key \
  -v /YOUR_WORKING_DIR:/var/sshpiper \
  farmer1992/sshpiperd

Quick start

Just run showme.sh in sshpiperd exmaple directory

$GOPATH/src/github.com/tg123/sshpiper/sshpiperd/example/showme.sh

the example script will setup a sshpiper server using

github@127.0.0.1:2222 -> pipe to github.com:22
linode@127.0.0.1:2222 -> pipe to lish-atlanta.linode.com:22

connect to linode

$ ssh 127.0.0.1 -p 2222 -l linode.com:22
linode@127.0.0.1's password:

connect to github.com:22

$ ssh 127.0.0.1 -p 2222 -l github
Permission denied (publickey).

Configuration

• sshpiperd manpage | man -l /dev/stdin

OPTIONS
   sshpiperd
       -l, --listen <default: "0.0.0.0">
              Listening Address

       -p, --port <default: "2222">
              Listening Port

       -i, --server-key <default: "/etc/ssh/ssh_host_rsa_key">
              Server key file for SSH Piper

       -u, --upstream-driver <default: "workingdir">
              Upstream provider driver

       -c, --challenger-driver <default: $SSHPIPERD_CHALLENGER>
              Additional challenger name, e.g. pam, empty for no additional challenge

       --auditor-driver <default: $SSHPIPERD_AUDITOR>
              Auditor for ssh connections piped by SSH Piper

       --log <default: $SSHPIPERD_LOG_PATH>
              Logfile path. Leave empty or any error occurs will fall back to stdout

       --config <default: "/etc/sshpiperd.ini">
              Config file path. Higher priority than arg options and environment variables

   upstream.workingdir
       --workingdir <default: "/var/sshpiper">
              Path to workingdir

       --workingdir-allowbadusername <default: $SSHPIPERD_WORKINGDIR_ALLOWBADUSERNAME>
              Disable username check while search the working dir

       --workingdir-nocheckperm <default: $SSHPIPERD_WORKINGDIR_NOCHECKPERM>
              Disable 0400 checking when using files in the working dir

   challenger.welcometext
       --challenger-welcometext <default: $SSHPIPERD_CHALLENGER_WELCOMETEXT>
              Show a welcome text when connect to sshpiper server

   auditor.typescript-logger
       --auditor-typescriptlogger-outputdir <default: "/var/sshpiper">
              Place where logged typescript files were saved

Files inside Working Dir

Working Dir is a /home-like directory. SSHPiperd read files from workingdir/[username]/ to know upstream's configuration.

e.g.

workingdir tree

.
├── github
│   └── sshpiper_upstream
└── linode
    └── sshpiper_upstream

when ssh sshpiper_host -l github, sshpiper reads workingdir/github/sshpiper_upstream and the connect to the upstream.

User files

These file MUST NOT be accessible to group or other. (chmod og-rwx filename)

• sshpiper_upstream

  • line starts with # are treated as comment
  • only the first not comment line will be parsed
  • if no port was given, 22 will be used as default
  • if user@ was defined, username to upstream will be the mapped one

# comment
[user@]upstream[:22]

e.g. 

git@github.com

google.com:12345

• authorized_keys

  OpenSSH format authorized_keys (see ~/.ssh/authorized_keys). Used for publickey sign again(see below).

• id_rsa

  RSA key for publickey sign again(see below).

Publickey sign again

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 will modify the sig using a private key (id_rsa) in the workingdir/[username]/.

How this work

+------------+        +------------------------+                       
|            |        |                        |                       
|   client   |        |   SSH Piper            |                       
|   PK_X     +-------->      |                 |                       
|            |        |      v                 |                       
|            |        |   Check PK_X           |                       
+------------+        |   in authorized_keys   |                       
                      |      |                 |                       
                      |      |                 |     +----------------+
                      |      v                 |     |                |
                      |   sign agian           |     |   server       |
                      |   using PK_Y  +-------------->   check PK_Y   |
                      |                        |     |                |
                      |                        |     |                |
                      +------------------------+     +----------------+

e.g.

on client

ssh-copy-id -i PK_X test@sshpiper

on ssh piper server

ln -s ~test/.ssh/authorized_keys workingdir/test/authorized_keys
ssh-keygen -N '' -f workingdir/test/id_rsa  # this is PK_Y
ssh-copy-id -i workingdir/test/id_rsa test@server

now ssh test@sshpiper -i -i PK_X, sshpiper will send PK_Y to server instead of PK_X.

Additional Challenge (--challenger-driver=)

ssh piper allows you run your own challenge before dialing to the upstream. if a client failed in this challenge, connection will be closed. however, the client has to pass the upstream server's auth in order to establish the whole connection. Additional Challenge is required, but not enough.

This is useful when you want use publickey and something like google-authenticator together. OpenSSH do not support use publickey and other auth together.

Available Challengers

• pam

  Linux-PAM challenger

  this module use the pam service called sshpiperd

  you can configure the rule at /etc/pam.d/sshpiperd

• welcometext

  Do nothing, but print a welcome text

SSH Session logging (--auditor-driver=typescript-logger)

When record_typescript is allowed, each piped connection would be recorded into typescript in working_dir.

The file format is compatible with scriptreplay(1)

Example:

$ ./sshpiperd  --record_typescript

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


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

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

TODO List

• live upgrade
• hostbased auth support
• ssh-copy-id support or tools
• challenger: menu challenger
• sshpiperd: user@subhost@host support