Secure Shell

X11_ssh_tunnelling

OpenWrtPuTTY

Ssh_binary_packet_alt

Secure Shell (SSH) is a cryptographic network protocol for operating network services securely over an unsecured network. The best-known application of SSH is for remote login to computer systems by users.

History

SSH was designed as a replacement for Telnet and other insecure remote shell protocols such as the Berkeley rlogin and rexec protocols, which send information, notably passwords, in plaintext, rendering them susceptible to interception and disclosure using packet analysis. The encryption used by SSH provides confidentiality and integrity of data over an insecure network, such as the Internet.

Functionality

SSH uses the client-server model. The standard TCP port for SSH is 22. An SSH client program is typically used for establishing connections to an SSH daemon accepting remote connections. Both the client and server authenticate each other using a variety of methods, including passwords, public keys, and certificates.

Authentication

SSH supports several authentication methods. The most common ones are:

• Password authentication
• Public key authentication
• Host-based authentication

Encryption

SSH uses strong encryption algorithms to ensure the security of data transmitted over the network. Commonly used algorithms include:

• AES
• Blowfish
• 3DES

Applications

SSH is used in various applications across many platforms, including:

• Remote command-line login
• Remote command execution
• Secure file transfer using SCP and SFTP
• Port forwarding/tunneling
• VPNs

Implementations

There are several implementations of SSH, both open-source and proprietary. The most widely used open-source implementation is OpenSSH, which is part of the OpenBSD project. Other notable implementations include:

• PuTTY
• Tectia SSH
• Dropbear

Security

SSH is considered highly secure when properly configured. However, it is essential to follow best practices, such as:

• Disabling root login
• Using strong passwords or key-based authentication
• Regularly updating the SSH software to patch vulnerabilities

See also

• Telnet
• OpenSSH
• SCP
• SFTP
• Public key infrastructure
• Cryptography

Related Pages

• Remote login
• Packet analysis
• Encryption
• Virtual private network
• OpenBSD