Telnet/SSH Connecting to Hosts Internet Technology

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) Internet Technology

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) Internet Technology

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

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 Internet Technology

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 Internet Technology

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 Internet Technology

SSH: Client-Server Architecture 11/8/2018 SSH: Client-Server Architecture SSH Client Initiates a Connection SSH Server Waits & Responds to Incoming Connections 203.247.16.240 155.230.194.245 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 Internet Technology

FTP/SFTP Transferring Files Internet Technology

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 e.g., login ID=anonymous, password=email address Suffers from security problem similar to Telnet Internet Technology

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) Internet Technology

PuTTY & SSH Secure File Transfer SSH & SFT Clients PuTTY & SSH Secure File Transfer Internet Technology

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 Internet Technology

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” Internet Technology

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. Internet Technology

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) Internet Technology

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 Internet Technology

SFTP Client: FileZilla Internet Technology

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. Internet Technology

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 Internet Technology

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. Internet Technology