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Npasswd is a replacement for the passwd command for UNIX. It subjects user passwords to stringent guessability checks to decrease the chance of users choosing vulnerable passwords. It addresses other deficiencies found of standard password change programs. Npasswd is designed to replace the programs passwd, chfn and chsh.
Npasswd should work under most versions of UNIX and UNIX-like operating systems. It does not replicate every feature of every password program on every UNIX platform. If the installer chooses to replace the system programs with npasswd, they will be preserved and used to perform the functions that npasswd cannot do.
Many UNIX platforms use shadow passwords, which makes it harder for a bad guy to obtain encrypted passwords. But there are still plenty of systems which have the encrypted passwords available for all the world to see.
Having shadow passwords in and of itself greatly reduces vulnerability to password crackers. But that protection is a function of the UNIX file system. If you use unsecure NIS or a misconfigured NIS+, you can still give away your passwords.
Combining intelligent password checking with a shadow database provides the best protection short of one-time use passwords or challenge/response smart card systems.
Configuring npasswd requires some thought on the part of the administrator. It's not a "plug and play" process. There are configuration options to select, and there is policy in the code that may not meet your needs.
In November of 1988 the infamous Morris worm escaped its playpen and went on a rampage across the Internet, bringing UNIX systems to their knees and causing widespread trouble. Among the Worm's attacks was a password guesser, which was fairly clever and unnervingly successful.
Our systems (University of Texas Academic Computing Servies) escaped being ravaged by the Worm because our main mail gateway was not a VAX or SUN.
Afterwards the Worm was dissected and papers released describing its anatomy. From these papers I replicated the password cracker, ran it against our password files and got plenty of hits. I rewrote the cracker into a primitive password checker that was posted to comp.sources.misc in 1989.
The UNIX password encryption crypt(3) was considered good that the cyphertext could not be cracked, so it was safe to have the encrypted passwords visible to all.
The Worm approached password cracking from a "human engineering" perspective. People are likely to choose passwords which are easy to remember - such as their login name or phone number. The Worm's password cracker encrypted various plaintext strings and compared them to the encrypted password. The plaintext came from user's passwd information and the UNIX spelling dictionary. This approach was fairly successful.
Our UNIX vendors were shipping the primitive V7 passwd program which did no significant password checking. This lack of vendor support meant the only way to have more secure passwords was to replace it. I wrote npasswd around my "worm" password checker.
By late 1989 npasswd had replaced /bin/passwd on all of our public UNIX systems. After a few sweeps with my password checker, some pointed email and other unfriendly actions, I and my colleagues breathed easier - at least for awhile.
In 1991 (or so) Crack was released and the world changed. It did not attempt to reverse the password encryption, but used a brute force attack similar to that of the Worm. Anyone with a 386 box (the hot commodity system of the time), a C compiler and some patience could crack passwords at their leisure.
I began to look into integrating Crack into npasswd. I found that npasswd needed serious updating - the UNIX environment was changing, and there had been plenty of porting problems.
I had also learned a lot more about C programming, so I decided that npasswd needed an extensive rewrite. That work started in July of 1993.
The rewrite was more complicated and taken over 5 years (off and on). All of the UNIX platforms which hosted the original npasswd have have been retired. There is new hardware (64-bit CPUs), new operating systems (Solaris 2, OSF/1), new user databases (NIS+) and security facilities.
These facilities are sophisticated and capable, but too often have unstable and/or undocumented programming interfaces - as well as difficult bugs to work around. Manipulating these databases is much more complex than updating field 2 of /etc/passwd.
Although some vendor password change utilities are better at disallowing easily guessed passwords, most still rely upon file system protections to keep the cyphertext away from prying eyes.
Vendors could make the life of a system administrator more pleasant by allowing the system administrator to interpose a site-specific password check policy.
The work of keeping up with new releases of UNIX systems and new features can take up a lot of time. I do not know if I will be able to continue this work.
A lot of people have contributed their work to npasswd over the years. I've got a large collection of variants of npasswd 1 done by lots of folks. Many have provided good ideas and code that have been incorporated into version 2.0.
Here are some of the more outstanding contributors that I can recall:
Alec Muffet for providing me Crack modules ready to use and a copious collection of word lists.
Paul Leyland of Oxford University, UK provided support for Ultrix enhanced security (which was the base for OSF/1 enhanced security support).
Donnie Emeson for adding character class diversity requirements to the password lexical check code.
Mike Stute for HP-UX support and some improvements to the dictionary lookup password checking.
One of the most popular variants of npasswd was produced at NASA Jet Propulsion Laboratory in Pasadena, California. Two guys who did a lot of the JPL work were Dan Kegel, who added Crack password checking and Dave Hayes who added SunOS 4 adjunct password support (among other things).
Tomasz Surmacz, Institute of Cybernetics, Technical Technical University of Wroclaw, Poland, contributed the password original history code.
Charles Seeger, University of Florida CIS Department and Steve Swartz, University of Wisconsin for supplying code to include chfn and chsh functionality.
There are many more who made suggestions and provided code that wasn't used, but whose comments were appreciated.
Documents on the Internet Worm:
Documents on password security:
Document id @(#) Main.html 1.8
Version 1.8
Last modified 07/20/98
Clyde Hoover