1. Telnet/SSH
Connecting to Hosts
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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.
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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3. Why Telnet? Telnet protocol made possible 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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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
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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 widit.knu.ac.kr 80
Connect to WIDIT Web Server
telnet rainmaker.wunderground.com
Access weather information
telnet sdf.lonestar.org
Create a shell account at SDF Public Access Unix System
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6. 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
Snooper
ID, password
Telnet Client 1
Banking info
Telnet Server
Telnet Client 2
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7. SecureSHell Overview Replacement for Telnet History Client Software
Communication between computers using encryption
Encryption = transform data in unreadable form
Communication is encrypted over a secure channel
Current standard for remote login (port 22)
Secure command shell (remote execution of commands)
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
MobaXterm
PuTTY
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8. SSH: Client-Server Architecture
11/8/2018
SSH: Client-Server Architecture
SSH Client
Initiates a Connection
SSH Server
Waits & Responds to Incoming Connections
Application Protocol
(SSH)
Client Application
Server Application
program running on
client machine
(e.g., Putty, SSH Secure Shell)
program running on
server machine
(e.g., Open SSH Server )
Encrypted Data
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9. FTP/SFTP
Transferring Files
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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 )
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
e.g., login ID=anonymous, password= address
Suffers from security problem similar to Telnet
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11. SFTP Overview Stands for SSH File Transfer Protocol Provides
Secure data transfer by data encryption over an SSH session
Replacement for FTP
SFTP Clients
GUI Interactive file transfer programs
Perform all operations over an encrypted transport
Examples
SSH Secure File Transfer (includes SSH client: SSH Secure Shell)
WinSCP – supports SFTP & SCP
FileZilla – cross platform (Windows, Linux, Mac OS)
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12. PuTTY & SSH Secure File Transfer
SSH & SFT Clients
PuTTY & SSH Secure File Transfer
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13. SSH Client: PuTTY PuTTY configuration Download and double click PuTTY
Type in the Host Name (e.g. widit.knu.ac.kr) and click Open
Login
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14. SSH Client: PuTTY PuTTY configuration (continued)
Right-click the top blue bar of the PuTTY window
Select “Change Settings”
Select “Translation” under Window Category
Set Character set translation to “UTF-8”
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15. SSH Client: PuTTY PuTTY configuration (continued)
Select “Appearance” under Window Category
Set Font settings to desired font if needed
Select “Colors” under Window Category
Set Default Foreground and Default Background to desired colors if needed
Click Apply to apply the current settings.
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16. SSH Client: PuTTY PuTTY configuration (continued)
Click the “Session” category
Type in a name for the current configuration (e.g., widit) in the “Saved Sessions” box
Click Save to save the current settings
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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17. SFTP Client: FileZilla
In the FileZilla’s main menu,
Click File and
select Site Manager.
In the Site Manager window,
Click New Site
Type in the Remote Host Name (e.g. widit.knu.ac.kr)
Select SFTP Protocol
Select Ask for password Logon Type
Type in your User Name (leave the password blank)
Click the Rename button
Type in a site name (e.g., widit)
Click Connect
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18. SFTP Client: FileZilla
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19. SFTP Client: FileZilla
Adding Bookmarks:
Go to target directories by typing in the path in the site address box (A) or traversing the directory tree (B).
Click Bookmarks and
Select Add bookmark.
Select Site-specific bookmark and
Type in the bookmark name
→ The saved bookmark should appear under the Bookmarks menu.
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20. SFTP Client: FileZilla
 displays saved site profile
 toggles the display of the message log
 toggles the display of the local directory tree
 toggles the display of the remote directory tree
 toggles the display of the transfer queue
 Refreshes the file and folder lists
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21. SFTP Client: FileZilla
Using Quickconnect:
In the Quickconnect bar,
 Type in Host name,
 Username,
 Password,
 Port value of 22,  Click the Quickconnect button,  and Click OK to connect.
 Click File in the Menu bar, and
 Select Copy current connection to Site Manager. In the Site Manager window,
 Type in the site name and
 Click OK.
→ The saved connection should appear in the Site Manager.
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