If we could restrict these services to a few trusted hosts, the risks of a break-in would be dramatically reduced. Because of their wrapper design, Venema's programs are very simple to set up. Once it has performed its form of authentication, tcpd passes off control to a forked in.telnetd just as inetd would do. Even if passwords never go out across the net unencrypted, it is always possible for an intruder to guess a user's password. There are numerous programs that take a dictionary and a username and try to log on as that user with every word in the dictionary.
Most users choose simple words as their passwords, unaware of the prevalence of dictionary attacks.
To avoid falling subject to these attacks, you must keep users from choosing simple passwords. By default, the passwd program will change any user's password, so the only way to prevent bad choices is to test them automatically, using the same tools intruders will use. Zimmerman was concerned about pending U.S. federal legislation that would make exporting encryption software illegal. He quickly coded and distributed the first PGP version out of devotion to the idea of civil liberties, starting distribution of its source and binaries before the law could take effect. The purpose of PGP is to encrypt documents.