Kerberos and Pluggable Authentication Modules (PAM)

Currently, kerberized services do not make use of PAM at all — a kerberized server bypasses PAM completely. Applications that use PAM can make use of Kerberos for password-checking if the pam_krb5 module (provided in the pam_krb5 package) is installed. The pam_krb5 package contains sample configuration files that will allow services like login and gdm to authenticate users and obtain initial credentials using their passwords. Provided that access to network servers is always done using kerberized services (or services that use GSS-API, like IMAP), the network can be considered reasonably safe.

Careful system administrators will not add Kerberos password-checking to network services, because most of the protocols used by these services do not encrypt the password before sending it over the network — obviously something you'd want to avoid.