1. Telnet/SSH: Connecting to Hosts Internet Technology1

2. What is Telnet? Method for connecting to hosts ► Enables remote login (rlogin) to computers on the Internet One computer can connect to another to use its services Like Window’s Remote Desktop ► Establishes a “dumb terminal” session No processing on the client side once connected Local terminal appears to be a terminal at the remote system.Local terminal appears to be a terminal at the remote system. Simple input/output device Client-Server Application ► Users (clients) connect to multiuser computers (servers) ► Uses telnet protocol (port 23) over Internet (TCP/IP) ► One of the first Internet applications (1968) Internet Technology 2

3. Why Telnet? Before PC became popular ► People used terminals physically connected to big computers (e.g., mainframes) ► Problems Need a terminal per machine per user  3 mainframes & 5 users = 15 terminals  Like having 10 TVs to view 10 channels Difficult to access over distance Telnet protocol made possible ► “terminal emulation” i.e., virtual terminal ► regardless of location & hardware  any computer running telnet client can connect to & use any computer running telnet server over Internet (TCP/IP, physical layer) Internet Technology 3

4. Telnet: Client-Server Architecture Telnet Server ► The actual server is software that runs typically on larger computers with multi-user, multi-tasking operating systems like Unix & a full-time/direct/high-speed connection to Internet ► May provide dumb terminal access to external data & services  library database or commercial service internal data & applications  files on disk, shell account Telnet Client ► The software that initiates a telnet connection ► Provides the interface and a set of features for the end user e.g., allow user to use custom fonts/colors Internet Technology 4

5. Telnet: How to Use telnet HOSTNAME PORTNUMBER ► HOSTNAME = host name or IP address ► PORTNUMBER = port Default telnet (login) port = 23 Web server port = 80 ► Examples telnet kiyang.kmu.ac.kr  Connect to KMU Web hosting services (login required) telnet www.kmu.ac.kr 80  Connect to KMU Web Server telnet sdf.lonestar.org  Create a shell account at SDF Public Access Unix System Internet Technology 5

6. Telnet: Weakness Telnet suffers from a major security problem ► Communication is done in plain text by a LAN computer using a snooper softwareData from/to client and server can be captured by a LAN computer using a snooper software Internet Technology 6 Telnet Client 1 Telnet Server Snooper ID, password Telnet Client 2 Banking info

7. S ecure SH ell Overview Replacement for Telnet ► Communicate with other computers using encryption Encryption = transform data in unreadable form ► Current standard for remote login Secure command shell (remote execution of commands) Secure file transfer History ► Originated from an academic project in Finland ► Commercialized in 1998 by SSH Communications Security ► SSH1 expired in May 1995 because of security flaws ► SSH2 is currently used Client Software ► SSH Client SSH Client ► PuTTY PuTTY Internet Technology 7

8. SSH Client Initiates a Connection SSH Server Waits & Responds to Incoming Connections Client ApplicationServer Application program running on client machine (e.g., Putty, SSH Secure Shell) Application Protocol (SSH) SSH: Client-Server Architecture 203.247.16.240 203.247.16.248 program running on server machine (e.g., Open SSH Server ) 8 Encrypted Data

9. FTP/SFTP: Transferring Files Internet Technology9

10. FTP Overview Used to transfer files from one computer to another ► Port 20, 21 - one to send data and one to send commands A basic Internet service (like telnet and email) ► Works with all types of computers (Unix, pc, mac, etc.) & all types of files (“binary” and “text”) ► One of the first Internet applications (1971) Involves ► Navigation on both client and server ► User authentication Exception: Anonymous FTP  Allows access to “public” FTP sites  Only allows access to specific directories  login ID=anonymous, password=email address Suffers from security problem similar to Telnet Internet Technology 10

11. SFTP Overview Stands for ► Secure File Transfer Protocol or SSH File Transfer Protocol Provides ► Secure data transfer by data encryption ► Replacement for FTP SFTP Clients ► GUI Interactive file transfer programs ► Perform all operations over an encrypted transport ► SSH Secure File Transfer (includes SSH client: SSH Secure Shell) SSH Secure File Transfer Internet Technology 11

12. SSH & SFT Clients: PuTTY & SSH Secure File Transfer Internet Technology12

13. SSH Client: PuTTY PuTTY configuration PuTTY 1. Download and double click PuTTY 2. Type in the Host Name (e.g. widit.knu.ac.kr) and click Open 3. Login Internet Technology 13

14. SSH Client: PuTTY PuTTY configuration (continued) PuTTY 4. Right-click the top blue bar of the PuTTY window 5. Select “Change Settings” 6. Select “Translation” under Window Category 7. Set Character set translation to “UTF-8” Internet Technology 14

15. SSH Client: PuTTY PuTTY configuration (continued) PuTTY 8. Select “Appearance” under Window Category 9. Set Font settings to desired font if needed 10. Select “Colors” under Window Category 11. Set Default Foreground and Default Background to desired colors if needed 12. Click Apply to apply the current settings. Internet Technology 15

16. SSH Client: PuTTY PuTTY configuration (continued) PuTTY 13. Click the “Session” category 14. Type in a name for the current configuration (e.g., widit) in the “Saved Sessions” box 15. Click Save to save the current settings 16. Next time, you can right-Click the top blue bar and select Saved Sessions to choose the appropriate session (e.g. widit) Internet Technology 16

17. SFTP Client: SSH Secure File Transfer SSH Secure File Transfer (includes SSH client) SSH Secure File Transfer 1. Click File, and select Connect 2. Type in the Remote Host Name (e.g. widit.kmu.ac.kr), User Name, and click Connect 3. Type in Password Internet Technology 17

18. SFTP Client: SSH SFTP SSH Secure File Transfer (continued) SSH Secure File Transfer 1. Click Profiles, and select Add Profile 2. Type in the profile name (e.g. widit-ftp) and click Add to Profiles 3. Next time, Click Profiles and select the saved profile name to connect Internet Technology 18