What is SSH (Secure Shell)? | SSH Academy
By Admin
Published: 2019-08-27 · Archived: 2026-04-05 17:52:18 UTC
This is the start page for the SSH (Secure Shell) protocol, software, and related information. SSH is a software
package that enables secure system administration and file transfers over insecure networks. It is used in nearly
every data center and in every large enterprise.
This page was created by the inventor of SSH, Tatu Ylonen (twitter: @tjssh). He wrote ssh-1.x and ssh-2.x, and
still works on related topics. The open source OpenSSH implementation is based on his free version.
The SSH protocol
The SSH protocol uses encryption to secure the connection between a client and a server. All user authentication,
commands, output, and file transfers are encrypted to protect against attacks in the network. For details of how the
SSH protocol works, see the protocol page. To understand the SSH File Transfer Protocol, see the SFTP page.
Download client software
https://www.ssh.com/ssh
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Here you can find links to download various free SSH implementations. We offer various free SSH
implementations for download, and provide links to commercial implementations.
Download PuTTY
Download SSH clients
List
of SSH implementations
We list various SSH implementations here. Feel free to submit additional implementations for this page. For many
implementations we offer a review, installation instructions, guidance, and/or how-tos on this site.
Tectia SSH client & server for Windows, Unix, Linux - with 24x7 support
Tectia SSH for IBM z/OS client & server for IBM z/OS mainframes - with 24x7 support
PuTTY client for Windows and Linux
WinSCP client for Windows
CyberDuck client for Mac
OpenSSH server for Unix, Linux
Overview of client alternatives
Overview of server alternatives
Windows SSH alternatives
PrivX™ Privileged Access Management for multi-cloud
Running & configuring SSH
https://www.ssh.com/ssh
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This section contains links topics around using, configuring, and administering SSH.
Command line options
Tectia SSH manuals
sshd - The SSH server on Unix/Linux
sshd_config - Server configuration file on Unix/Linux
ssh_config - Client configuration file on Unix/Linux
SSH port, and how it got that number
Security of SSH and attacks against it
The SSH protocol is believed to be secure against cryptographic attacks on the network, provided keys and
credentials are properly managed. However, we do not recommend using diffie-hellman-group1-sha1 key
exchange. It uses a 768 bit Diffie-Hellman group, which may be breakable by governments today. Larger groups
are probably ok. Recent OpenSSH versions have disabled this group by default. See sshd_config for configuring
what key exchanges to use.
Analysis of BothanSpy and Gyrfalcon - the presumed CIA hacking tools
Man-in-the-middle attacks against SSH
Imperfect forward secrecy - How Diffie-Hellman fails in practice
Automate with SSH keys, but manage them
SSH keys can be used to automate access to servers. They are commonly used in scripts, backup systems,
configuration management tools, and by developers and sysadmins. They also provide single sign-on, allowing the
https://www.ssh.com/ssh
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user to move between his/her accounts without having to type a password every time. This works even across
organizational boundaries, and is highly convenient.
However, unmanaged SSH keys can become a major risk in larger organizations.
What is an SSH key
What SSH life cycle management means
Universal SSH Key Manager
ssh-keygen - Create keys
ssh-copy-id - Provision access on servers
authorized_keys - Authorized keys file format
The PrivX On-Demand Access Manager can be used as an alternative for SSH keys, eliminating the need for
permanent keys and passwords on servers entirely.
History of the SSH protocol
The Secure Shell protocol was originally developed by Tatu Ylonen in 1995 in response to a hacking incident in
the Finnish university network. A password sniffer had been installed on a server connected directly to the
backbone, and when it was discovered, it had thousands of usernames and passwords in its database, including
several from Ylonen's company.
That incident triggered Ylonen to study cryptography and develop a solution he could use himself for remote login
over the Internet safely. His friends proposed additional features, and three months later, in July 1995, Ylonen
published the first version as open source. It became OpenSSH. Later he took the protocol for standardization at
the IETF and designed the SSH File Transfer Protocol (SFTP). He founded SSH Communications Security Corp
in December 1995 to provide commercial support for the protocol.
Ylonen still works on topics related to Secure Shell, particularly around key management, as well as broader
cybersecurity topics.
Today, the protocol is used for managing more than half of world’s web servers and practically every Unix or
Linux computer, on-premise and in the cloud. Information security specialists and system administrators use it to
configure, manage, maintain, and operate most firewalls, routers, switches, and servers in the millions of mission-critical networks and environments of our digital world. It is also embedded inside many file transfer and systems
management solutions.
The new protocol replaced several legacy tools and protocols, including telnet, ftp, FTP/S, rlogin, rsh, and rcp.
Source: https://www.ssh.com/ssh
https://www.ssh.com/ssh
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