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Every request to an NIS+ server is made by an NIS+ principal. An NIS+ principal can be a user or a workstation. Authentication is the process of identifying the principal who made a request to the NIS+ server by checking the principals credentials. These credentials are based on encrypted verification information stored in the NIS+ cred table.
The purpose of authentication is to obtain the principals name so that access rights to information in the name server can be looked up and verified. All interactions that an NIS+ principal has with an NIS+ server are authenticated.
The benefit of authentication is the protection of NIS+ information from access by untrusted clients, which provides more flexible and secure administration of NIS+ servers.
NOTE: Protection of resource information in NIS+ does not imply protection of the resource itself. For example, protecting information about a server does not protect the server itself.
Principals can have two types of credentials: LOCAL and DES. A LOCAL credential consists of the UID of an NIS+ principal. An NIS+ server uses the LOCAL UID credential to look up the identity of the principal who sent the request so that the NIS+ server can determine the principals rights to access the requested object.
A DES credential is more complicated, and both users and systems can have such credentials. The DES credential consists of the principals secure RPC netname and a verification field.
Table 5-4 shows the columns in the cred table and describes the type of information stored for LOCAL and DES authentication.
|NIS+ principal name of a client user||LOCAL||UID||GID list||None|
|NIS+ principal name of a client user or client system||DES||Secure RPC netname||Public key||Encrypted Private key|
The first column, cname, contains the fully qualified credential name of an NIS+ principal. When the authentication type is LOCAL, the first column can only contain usernames because client systems cannot have LOCAL credentials. When the authentication type is DES, the principal name can be either a username or a system name.
The following example shows the contents of the cred table on the system named oak. The fields are separated by colons.
oak% niscat -h cred.org_dir # cname:auth_type:auth_name:public_data:private_data oak.ESG.Eng.sun.COM.:DES:unix.oak@ESG.Eng.sun.COM:5c8349c1eØ eb851a1717Øefb5a8dd63e44721Ø341e565eaf::f8f133ebb68679c958 ea4c5e43d61aad5b76c17bba4ffdefad27edc2fcd89ccØ winsor.ESG.Eng.sun.COM.:LOCAL:6693:1,14: winsor.ssi.eng.sun.com.:DES:email@example.com:aacf4fcdc 47811b255Øf443bca4d28c1a8fcf287e81dec24::b11a448aØ4877fd3dfc48c 599fa18cad3d7e7431ebaac7492d731dc2f6Ø51761 ignatz.DGDO.Eng.sun.COM.:LOCAL:6694:1: oak%
The first entry shows the names of the columns in the cred table. The second entry is the DES authentication for the system oak. The third and fourth entries are LOCAL and DES authentication entries for the user winsor. The fifth entry is LOCAL authentication for user ignatz, who has an account on the system. User ignatz does not have DES authentication credentials in the local domain. Only a LOCAL cred entry is needed if the users home domain is not the local one.
NIS+ security privileges are assigned in two stages: The principal is authenticated (identified) as an authorized user, and the access rights are checked.
Figure 5-7 shows a simplified view of how NIS+ security works.
Figure 5-7 How NIS+ security works.
NIS+ classifies NIS+ principals into four authorization categories, as shown in Table 5-5.
|n||Nobody||A category reserved for unauthenticated requests.|
|o||Owner||A single NIS+ principal, who was the creator of the object. You can change the ownership of existing objects using the nischown command.|
|g||Group||A collection of NIS+ principals, grouped together to provide access to the namespace. When an object is created, it is by default assigned to the NIS+ principals default group. NIS+ group information is stored in the NIS+ group object in the groups_dir subdirectory of every NIS+ domain.|
|w||World||All NIS+ principals that are authenticated by NIS+.|
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