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apply policy restrictions. Also, we only show one Proxy zone; again, there could
be multiple lateral Proxy zones. In the example, we have two Data Access
zones, so the host in Data Access zone 2 is isolated by a firewall from the hosts
in Data Access zone 1. Another thing you should notice is that there is no direct
path from the Intranet zone to the Internet. This example shows an architecture
where all data flows must pass through a proxy server. Some organizations
allow direct connections from Intranet workstations to Web servers in the Internet
zone. If this was the case, the top-most firewall in the diagram would need a
connection to one of the lower two firewall routers.
4.2.5 Data access models
Categorizing data flows requires us to identify the authentication requirements,
the authentication entity types, and data classification and access models. We
need to make these distinctions to be able to formulate our final policies for
inter-zone communication. We previously discussed single-factor authentication
and dual-factor authentication in 1.3.3, “Identification and authentication” on
page 19. You should understand these two authentication types since they are
referenced as we continue to build our security architecture model.
Authentication entities
Following are some additional terms needed to distinguish the authentication
entity types.
Client-to-server authentication
We define this authentication type as a user (meaning an individual) being
authenticated by the server or an application or service on the server. The
authentication may consist of a challenge-response dialog method, or the client
may provide credentials to the server in the form of a certificate or other verifiable
token. A certificate could be an X.509 user certificate or a Notes certificate. An
example of a “verifiable token” would be an LTPA token HTTP session cookie.
The authentication process verifies the identity of the user. Note that this
authentication may or may not provide a means for the user to verify the identity
or trustworthiness of the server.
Server-to-server authentication
This type of authentication is the means by which one server can verify the
identity of another server. It uses some form of certificate, such as X.509 or
Notes. There is no password challenge-response method in this model. Note that
this type of authentication may be uni-directional or bi-directional. In a
bi-directional authentication, each server verifies the identity of the other.
Chapter 4. Security components and layers 149