Red Hat CERTIFICATE SYSTEM 8 - DEPLOYMENT Deployment Manual page 16

Chapter 1. Introduction to Public-Key Cryptography
a server. Server authentication refers to the identification of a server (the organization assumed to be
running the server at the network address) by a client.
Client and server authentication are not the only forms of authentication that certificates support. For
example, the digital signature on an email message, combined with the certificate that identifies the
sender, can authenticate the sender of the message. Similarly, a digital signature on an HTML form,
combined with a certificate that identifies the signer, can provide evidence that the person identified by
that certificate agreed to the contents of the form. In addition to authentication, the digital signature in
both cases ensures a degree of nonrepudiation; a digital signature makes it difficult for the signer to
claim later not to have sent the email or the form.
Client authentication is an essential element of network security within most intranets or extranets.
There are two main forms of client authentication:
• Password-based authentication . Almost all server software permits client authentication by
requiring a recognized name and password before granting access to the server.
• Certificate-based authentication . Client authentication based on certificates is part of the SSL
protocol. The client digitally signs a randomly generated piece of data and sends both the certificate
and the signed data across the network. The server validates the signature and confirms the validity
of the certificate.
1.3.2.1. Password-Based Authentication
Figure 1.4, "Using a Password to Authenticate a Client to a Server"
authenticating a user using a username and password. This example assumes the following:
• The user has already trusted the server, either without authentication or on the basis of server
authentication over SSL.
• The user has requested a resource controlled by the server.
• The server requires client authentication before permitting access to the requested resource.
Figure 1.4. Using a Password to Authenticate a Client to a Server
These are the steps in this authentication process:
1. When the server requests authentication from the client, the client displays a dialog box requesting
the username and password for that server.
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shows the process of