3Com WX3000 operation manual Asymmetric Key Algorithm, SSH Operating Process, Stages Description

Figure 1-1Encryption and decryption

Key

Cipher text

Plain textEncryption

Key

Decryption Plain text

Key-based algorithm is usually classified into symmetric key algorithm and asymmetric key algorithm.

Asymmetric Key Algorithm

Asymmetric key algorithm means that a key pair exists at both ends. The key pair consists of a private key and a public key. The public key is effective for both ends, while the private key is effective only for the local end. Normally you cannot use the private key through the public key.

Asymmetric key algorithm encrypts data using the public key and decrypts the data using the private key, thus ensuring data security.

You can also use the asymmetric key algorithm for data signature. For example, user 1 adds his signature to the data using the private key, and then sends the data to user 2. User 2 verifies the signature using the public key of user 1. If the signature is correct, this means that the data originates from user 1.

Both Revest-Shamir-Adleman Algorithm (RSA) and Digital Signature Algorithm (DSA) are asymmetric key algorithms. RSA is used for data encryption and signature, whereas DSA is used for adding signature.

Currently, SSH supports both RSA and DSA.

SSH Operating Process

The session establishment between an SSH client and the SSH server involves the following five stages:

Table 1-1Stages in establishing a session between the SSH client and server

Stages		Description
Version negotiation		SSH1 and SSH2 are supported. The two parties negotiate a version to use.
Key and algorithm		SSH supports multiple algorithms. The two parties negotiate an algorithm for
negotiation		communication.
Authentication		The SSH server authenticates the client in response to the client’s
		authentication request.
Session request	This client sends a session request to the server.
Data exchange		The client and the server start to communicate with each other.
	1-2