Telnet/SSH:Connecting to Hosts

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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.• 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)

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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)

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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

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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

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Telnet: Weakness Telnet suffers from a major security problem

► Communication is done in plain text• Data from/to client and server can be captured by

a LAN computer using a snooper software

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Telnet Client 1

Telnet Server

Snooper

ID, password

Telnet Client 2

Banking info

SecureSHell 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► PuTTY

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Internet Technology

SSH ClientInitiates a Connection

SSH Server Waits & Responds to Incoming Connections

Client Application Server Applicationprogram 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 )

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Encrypted Data

FTP/SFTP: Transferring Files

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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

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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)

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SSH & SFT Clients:PuTTY & SSH Secure File Transfer

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SSH Client: PuTTY PuTTY configuration

1. Download and double click PuTTY 2. Type in the Host Name (e.g. widit.knu.ac.kr) and click Open3. Login

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SSH Client: PuTTY PuTTY configuration (continued)

4. Right-click the top blue bar of the PuTTY window5. Select “Change Settings”6. Select “Translation” under Window Category7. Set Character set translation to “UTF-8”

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SSH Client: PuTTY PuTTY configuration (continued)

8. Select “Appearance” under Window Category9. Set Font settings to desired font if needed10. Select “Colors” under Window Category11. Set Default Foreground and Default Background to desired colors if needed12. Click Apply to apply the current settings.

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SSH Client: PuTTY PuTTY configuration (continued)

13. Click the “Session” category14. Type in a name for the current configuration (e.g., widit) in the “Saved Sessions” box15. 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)

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SFTP Client: SSH Secure File Transfer SSH Secure File Transfer (includes SSH client)

1. Click File, and select Connect2. Type in the Remote Host Name (e.g. widit.kmu.ac.kr), User Name, and click Connect3. Type in Password

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SFTP Client: SSH SFTP SSH Secure File Transfer (continued)

1. Click Profiles, and select Add Profile2. Type in the profile name (e.g. widit-ftp) and click Add to Profiles3. Next time, Click Profiles and select the saved profile name to connect

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