These tools are required to be able to login and use your system. The login program invokes your user shell and enables command execution. The newgrp program is used to change your effective group ID (useful for workgroup type situations). The su program allows changing your effective user ID (useful being able to execute commands as another user).
passwd | change and administer password and group data | Mehr ...
This package includes passwd, chsh, chfn, and many other programs to maintain password and group data. . Shadow passwords are supported. See /usr/share/doc/passwd/README.Debian