What is the SSH protocol? Explanation of core concepts and application scenarios

in the scenario of digital operation and maintenance and teleworking, secure remote connection is the core requirement to ensure data and system stability. Many operation and maintenance personnel and developers will come into contact with a technology that can establish a secure communication channel in an insecure network, which is the SSH protocol. This article will explain the technical details and practical value of the SSH protocol from the core concept, encryption mechanism, application scenarios to security configuration and other dimensions, and help you quickly master this essential cyber security tool.

, SSH protocol core concept and origin?

to understand the role of SSH protocol, we must first start from its definition and birth background, which can help us understand what it solves the pain points of traditional remote connections.

1, the basic definition of SSH protocol

SSH protocol full name Secure Shell, is a network security protocol based on the application layer and transport layer, mainly used in the insecure network environment, for remote login, command execution, file transfer and other operations to provide encrypted communication channels, to avoid data eavesdropping, tampering or forgery.

2, the origin background of SSH protocol

before the SSH protocol appeared, Telnet, FTP and other protocols were commonly used for remote management, but these protocols were plaintext to transmit data, account passwords and operation instructions were easily intercepted, and there were great security risks. In 1995, to solve this problem, Finnish researcher Tatu Ylönen developed the first version of the SSH protocol, and then after continuous iterations, it gradually became the industry standard for remote secure connections.

What are the encryption mechanisms of the SSH protocol?

SSH protocol is a strong encryption system, which is the key to ensuring communication security.

1, asymmetric encryption authentication

SSH protocol uses asymmetric encryption to complete authentication in the early stage of establishing a connection. The server will generate a pair of public and private keys, which are public to the outside world, and the private key is kept by the server. When the client side connects to the server for the first time, it will obtain the server's public key, and then each connection will verify the server's identity through the public key to avoid man-in-the-middle attacks. At the same time, users can also generate their own key pair and upload the public key to the server to achieve password-free secure login.

2, symmetric encrypted session communication

authentication is completed, the SSH protocol will switch to symmetric encryption for subsequent session communication. This is because asymmetric encryption is slower, while symmetric encryption is more efficient and can meet the needs of large-scale data transmission. During the session, the client side and the server will negotiate to generate a temporary symmetric key, and all subsequent operation data will be encrypted and transmitted through this key to ensure that the communication content cannot be cracked by third parties.

Typical application scenarios of SSH protocol?

in addition to the most basic remote login, SSH protocol has many extended practical scenarios, covering operation and maintenance, development, data transmission and other fields.

1, server remote operation and maintenance management

this is the most commonly used scenario of SSH protocol, operation and maintenance personnel can remotely log in to Cloud as a Service, physical server or network device through SSH protocol to perform system configuration, software installation, log viewing and other operations. Whether it is Linux or Unix system, SSH protocol is the default remote management tool, ensuring the security and convenience of operation and maintenance operations.

2, secure file transfer and synchronization

SFTP and SCP tools derived from the SSH protocol to achieve secure file transfer. SFTP is the file transfer subsystem of the SSH protocol, which supports functions such as breakpoint continuation and directory list viewing; SCP is more suitable for fast transfer of single or multiple files. Compared with traditional FTP, both tools transfer data through the encrypted channel of the SSH protocol, avoiding the risk of file content theft.

3, automated operation and maintenance and script execution

in the automated operation and maintenance scenario, the SSH protocol can cooperate with tools such as Ansible and SaltStack to realize the operation execution of batch servers. The operation and maintenance personnel can write automated scripts, run synchronously on multiple servers remotely through the SSH protocol, complete software upgrades, configuration updates and other tasks, greatly improve the operation and maintenance efficiency, and ensure the security of the operation throughout the process.

How to ensure the security of SSH protocol?

although the SSH protocol itself has high security, if it is not configured properly, there may still be security bugs, so you need to master some key security configuration skills.

1, disable password login enable key authentication

password login is at risk of being brute-force, while the key verification method of the SSH protocol is more secure. Users can generate a key pair of type RSA or ED25519, upload the public key to the specified directory of the server, and then disable password login in the server configuration file. Only key login is allowed to avoid the risk of password leakage from the root cause.

2, modify the default port and limit login IP

SSH protocol uses port 22 by default, which is easy to be the target of hacker scanning attacks. Users can modify the listening port of the SSH protocol to an uncommonly used port number, and configure rules in the server firewall or security group to allow only devices with a specified IP or IP segment to connect to the SSH protocol, which greatly reduces the probability of malicious attacks.

To sum up, SSH protocol is the core tool to ensure the security of network remote operation. From the core encryption mechanism to various application scenarios, to the key security configuration, each link revolves around data security and operation convenience. Mastering the use of SSH protocol and security configuration skills can not only improve the efficiency of server operation and maintenance, but also build a solid security barrier for the system and data. It is one of the necessary technical capabilities for operation and maintenance personnel and developers.