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Introduction to Kerberos

Kerberos provides a toolkit for reducing the risks associated with insecure networks. It provides a unified password space in which we can manage strong passwords easily and it can prevent your password from being sent across the network as cleartext.

Working with Kerberos

When you successfully log into any of our kerberos authenticated systems, you will be granted a set of credentials which will identify you to other network resources. Most users can take advantage of Kerberos without any detailed knowlege about the system.

The only significant complication for some users is that credentials expire after one week at UMIACS. In some environments, the lack of credentials can cause the user environment to behave erratically as network resources become unavailable.

Whenever possible, we strongly suggest that users log out of their environments nightly.

Password Policies

We have the following policies in regards to our passwords,

  • Maximum Ticket Lifetime : 21days

This is the longest you can get a Kerberos Ticket for, after that you have to renew your tickets or re-authenticate.

  • Minimum Password Length : 8 Characters

This requires that your password is a minimum of 8 characters (it can have more just not less)

  • Minimum Character Classes : 3 Character Classes

Requires that a password have more than 3 character classes they include: lower-case letters, upper-case letters, digits and punctuation.

  • Number of Previous Passwords Kept: 5

Kerberos will store your last 5 passwords and will not let you set a new password to them, please choose a new password.

Listing your credentials

It is often useful to examine your current credentials. Using klist, you can verify that your login is correct ,

 [derek@kiwi ~]$ klist
 Ticket cache: FILE:/tmp/krb5cc_2174_dcDWCg
 Default principal: derek@UMIACS.UMD.EDU
 Valid starting     Expires            Service principal
 05/28/08 11:39:36  05/29/08 11:39:36  krbtgt/UMIACS.UMD.EDU@UMIACS.UMD.EDU
 Kerberos 4 ticket cache: /tmp/tkt2174
 klist: You have no tickets cached

'Default principal' indicates the kerberos identity of the current process. In this case, the kerberos pricipal, 'derek@UMIACS.UMD.EDU' indicates that I am authenticated as the user 'derek' to the realm 'UMIACS.UMD.EDU'.

If my credentials have not been set up correctly, klist will report:

 [derek@kiwi ~]$ klist
 klist: No credentials cache found (ticket cache FILE:/tmp/krb5cc_2174_dcDWCg)
 Kerberos 4 ticket cache: /tmp/tkt2174
 klist: You have no tickets cached

Reinitialize your Credentials

When available, use kinit -R to refresh your current credentials.

Single Sign On Services

Kerberos authenticated IMAP and SMTP provide secure and convenient methods sending and reading mail. Unlike traditional IMAP and SMTP services, your password is never sent over the network as cleartext and your password is not cached on a client.

Password Security

Kerberos security depends on the security of your password. Although Kerberos can make secure access to services convenient, it is still your responsibility to secure your password. Please try to choose a strong password and use secure protocols.