1. Firewalls, Perimeter Protection, and VPNs - SANS ©2001 1 SSH Operation The Swiss Army Knife of encryption tools…

2. Firewalls, Perimeter Protection, and VPNs - SANS ©2001 2 SSH Features Command line terminal connection tool Replacement for rsh, rcp, telnet, and others All traffic encrypted Both ends authenticate themselves to the other end Ability to carry and encrypt non- terminal traffic

3. Firewalls, Perimeter Protection, and VPNs - SANS ©2001 3 Brief History SSH.com’s SSH1, originally completely free with source code, then license changed with version 1.2.13 SSH.com’s SSH2, originally only commercial, but now free for some uses. OpenSSH team took the last free SSH1 release, refixed bugs, added features, and added support for the SSH2 protocol.

4. Firewalls, Perimeter Protection, and VPNs - SANS ©2001 4 Installation OpenSSH is included with a number of Linux distributions, and available for a large number of Unices On RPM-based linuxes: –“rpm –Uvh openssh*.rpm”

5. Firewalls, Perimeter Protection, and VPNs - SANS ©2001 5 Basic use ssh SshServerName ssh –l UserName SshServerName ssh SshServerName CommandToRun ssh –v SshServerName Server Host Key checks Uses same login password And if we need to encrypt other traffic?

6. Firewalls, Perimeter Protection, and VPNs - SANS ©2001 6 Port Forwarding – real server on remote machine I want to listen on port 5110 on this machine; all packets arriving here get sent to mailserver, port 110: –ssh –L 5110:mailserver:110 mailserver

7. Firewalls, Perimeter Protection, and VPNs - SANS ©2001 7 Port Forwarding – real server on this machine All web traffic to my firewall should be redirected to the web server running on port 8000 on my machine instead: –ssh –R 80:MyMachine:8000 firewall

8. Firewalls, Perimeter Protection, and VPNs - SANS ©2001 8 X Windows forwarding No setup – already done! Run the X Windows application in the terminal window: –xclock & –The screen display shows up on your computer, and any keystrokes and mouse movements are sent back, all encrypted.

9. Firewalls, Perimeter Protection, and VPNs - SANS ©2001 9 Securely copying files scp scp –p localfile remotemachine:/remotepath/file Prompts for authentication if needed All traffic encrypted Replaces ftp, rcp, file sharing

10. Firewalls, Perimeter Protection, and VPNs - SANS ©2001 10 SSH key background Old way: password stored on server, user supplied password compared to stored version New way: private key kept on client, public key stored on server.

11. Firewalls, Perimeter Protection, and VPNs - SANS ©2001 11 SSH key creation General command: –ssh-keygen –b 1024 –c “Comment” –f ~/.ssh/identity_file Different forms for each of the SSH flavors Assign a hard-to-guess passphrase to the private key during creation. Key can be used for multiple servers

12. Firewalls, Perimeter Protection, and VPNs - SANS ©2001 12 SSH key installation 3 versions of ssh: interoperability is good, but poorly documented ssh-keyinstall utility automates the creation and installation –“ssh-keyinstall –s SshServerName” creates keys, if needed, and installs them on the remote server –Need password during key install only

13. Firewalls, Perimeter Protection, and VPNs - SANS ©2001 13 Using SSH keys ssh SshServerName Ssh –l UserName SshServerName ssh SshServerName CommandToRun Ssh –v SshServerName

14. Firewalls, Perimeter Protection, and VPNs - SANS ©2001 14 ssh-agent Remembers your private key(s) Other applications can ask ssh-agent to authenticate you automatically. Unattended remote sessions. ssh-agent bash ssh-agent startx eval `ssh-agent`#Less preferred ssh-add [KeyName]

15. Firewalls, Perimeter Protection, and VPNs - SANS ©2001 15 Fanout Runs command on multiple machines by opening separate ssh session to each fanout “machine1 machine2 user@machine3” “command params” Gives organized output from each machine

16. Firewalls, Perimeter Protection, and VPNs - SANS ©2001 16 File synchronization - Rsync Rsync copies a tree of files from a master out to a copy on another machine. Can use ssh as its transport. rsync –azv –e ssh /home/wstearns/webtree/ mirror.stearns.org/home/web/

17. Firewalls, Perimeter Protection, and VPNs - SANS ©2001 17 Rsync-backup Rsync-backup automates the process of backing up machines with rsync and ssh. Features: –Only changed data shipped –All permissions preserved –All communication encrypted –Unlimited snapshots –Use <= 2X-4X combined client capacity

18. Firewalls, Perimeter Protection, and VPNs - SANS ©2001 18 Rsync-backup client install Install ssh, rsync, and rsync- backup-client rpms (see http://www.stearns.org http://www.stearns.org Install ssh-keyinstall on client to create a backup key with – ssh-keyinstall –s backupserver –u root –c /usr/sbin/rsync-backup-server

19. Firewalls, Perimeter Protection, and VPNs - SANS ©2001 19 Rsync-backup server install Install ssh, freedups, rsync-static, and rsync-backup-server rpms Turn off password authentication in /etc/ssh/sshd_config

20. Firewalls, Perimeter Protection, and VPNs - SANS ©2001 20 Rsync-backup examples Examples of backup commands: – rsync-backup-client / root@backupserver:/ – rsync-backup-client /usr /home/gbk root@backupserver:/

21. Firewalls, Perimeter Protection, and VPNs - SANS ©2001 21 Links and references http://www.ssh.com http://www.openssh.org SSH, The Secure Shell, The Definitive Guide ssh-keyinstall, fanout, rsync- backup, freedups and other apps at http://www.stearns.org/ http://www.stearns.org/

22. Firewalls, Perimeter Protection, and VPNs - SANS ©2001 22 More links Docs at http://www.stearns.org/doc/ http://www.stearns.org/doc/ http://www.employees.org/~satch/ ssh/faq/ssh-faq.htmlhttp://www.employees.org/~satch/ ssh/faq/ssh-faq.html http://rsync.samba.org William Stearns wstearns@pobox.com wstearns@pobox.com