The difference between SSH and Telnet

simple carcass, ssh and telnet are the same functions, SSH data is encrypted, is secure, and Telnet is transmitted in plaintext
SSH is encrypted and SSL-based.
Telnet is a plaintext transmission, the data sent by the listener does not need to decrypt to see the content.

Two are not common, and now it is not recommended to use Telnet.
Because now the network monitoring means very developed. And it's easy for the middle man to attack.

= = The following is quoted = =
Secure Sockets Layer (secure Sockets LAYER,SSL) and its successor Transport Layer Security (Transport layer Security,tls) is a security protocol that provides security and data integrity for network traffic. TLS encrypts the network connection with SSL at the transport layer.
==============
TLS uses key algorithms to provide endpoint identity authentication and communication secrecy on the Internet, based on public Key Infrastructure (PKI). In a typical example of implementation, however, only network services are reliably authenticated, and their clients are not necessarily. This is because the public key infrastructure is generally commercially operating, and electronic signature certificates are expensive to buy, and a certificate that the general public can hardly afford. The protocol is designed to to some extent enable the client/server application communication itself to prevent eavesdropping, interference (tampering), and message forgery.

TLS consists of three basic stages:

1. Key algorithm for peer negotiation support
2. Private key encryption Exchange public key, PKI certificate-based identity authentication
3. Confidentiality of data transmission based on public key cryptography

In the first phase, the client negotiates the password algorithm with the server. The currently widely implemented algorithms are selected as follows:

* Public key security system: RSA, Diffie-hellman, DSA and Fortezza;
* Private key security system: RC2, RC4, Idea, Des, Triple des and AES;
* One-way hash function: MD5 and SHA.
==========
The following is a brief description of how the SSL protocol works. The client wants to send and receive several handshake signals:

* Send a ClientHello message that describes the list of cryptographic algorithms it supports, the compression method, and the highest protocol version, and also sends a random number that will be used later.
* Then received a Serverhello message containing the connection parameters selected by the server, originating from the ClientHello provided by the client initially.
* When both parties know the connection parameters, the client exchanges the certificate with the server (depending on the selected public key System). These certificates are usually based on the OpenPGP, but there are already drafts that support certificates based on the.
* The server requests the client public key. The client has a certificate, two-way authentication, and a public key is randomly generated without a certificate.
* The client and server negotiate a common primary private key through public key secrecy (both sides are randomly negotiated), which is implemented by carefully designed pseudo-random number functions. The result may be a diffie-hellman interchange, or a simplified public key encryption, each of which decrypts with the private key. This "Master key" is used for all other key data encryption.

The record layer in data transfer is used to encapsulate protocols such as higher-level HTTP. The recording layer data can be compressed, encrypted, and compressed together with the message verification code. Each record-level package has a content-type segment to record the protocol for the higher layer.

Tls/ssl has a variety of safety measures:

* All record-level data are numbered for message verification code validation.
= = = Quote Complete = =
The above refers to the self-dimension (anti-diarrhea patch) base (anti-blood-drink patch) hundred (anti-nuclear break patch) Section

-------------------------------------------------

SSH1 and SSH2 are two security-level versions.
SSH2 is more secure. But it seems that some of the system's SSH2 support is to be charged separately for use.

Telnet port By default is, SSH and Telnet incompatible, so he was designed to be the default 22 port for the difference.

SSH when to use depends on when you want to link the server, and when the server to open the SSH service.

SSH only theory, no actual content, if you want the actual content, please look at the relevant algorithm part of TLS.
SSH is a remote control method that uses an encryption protocol based on a network layer.

As for the link is not up, it depends on how not to link:
1, whether the server's SSH service is started
2. Whether the firewall is open port
3, the network is unobstructed
4, whether the user can be remotely linked to SSH control
5, whether the port is 22
6, client software is compatible with server-side software
7 、......
8 、............

SSH sometimes just a transition transfer protocol, set up, you can also link to the remote server in SSH graphical interface for graphical operation. However, it is necessary to install the appropriate support program, and to set the appropriate settings, but also to open the appropriate features.

Telnet is of course good, not encryption is always the best use. You can't even know when a hijacked server is being hijacked by someone listening to you. Because the Telnet link is the direct white send the user name and password. Be aware that all the data sent by the hub inside the LAN is broadcast to all the network cards that are linked to the hub to send all the data. This time, do not need any hacker knowledge, find a listening software can directly intercept your password.

The difference between SSH and Telnet