Secure Shell (Secure Shell Protocol, SSH for short) is an encrypted network transmission protocol that can provide security for network services in insecure networks. transmission environment. SSH enables the connection between the SSH client and the server by creating a secure tunnel in the network. Although any network service can be transmitted securely through SSH, the most common use of SSH is to log in to the system remotely, and people usually use SSH to transmit command line interfaces and execute commands remotely.
The most frequently used situations are Unix-like systems, but Windows operating systems can also use SSH to a limited extent. In 2015, Microsoft announced that it would provide native SSH protocol support in future operating systems. Windows 10 version 1809 already provides OpenSSH tools that can be installed manually.
By design, SSH is a replacement for Telnet and non-secure shells. Telnet and Berkeley rlogin, rsh, rexec and other protocols use clear text transmission and use unreliable passwords, which are prone to monitoring, sniffing and man-in-the-middle attacks. SSH is designed to ensure complete and reliable encryption of information in non-secure network environments (such as the Internet).
However, SSH has also been pointed out to be vulnerable to sniffing and even decryption. As early as 2011, China's Internet censorship agencies already had the ability to detect and interfere with SSH connections. Documents later leaked by Edward Snowden also pointed out that the NSA was sometimes able to decrypt information transmitted by the SSH protocol and thus read the transmission content of the SSH session. On July 6, 2017, the non-profit organization WikiLeaks confirmed that the CIA had developed tools capable of stealing SSH sessions in Windows or Linux operating systems.
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