...
One method of cracking a password is to go through a series of possible
passwords, encrypting each by the known method, until the encrypted text
matches what is stored on the computer. It would definitely take a while
to crack a password on a mere home computer.
...
Um ... yes. And all an administrator has to do is limit
the number of tries to, say, three before shutting down
the attempt, with penalties of varying severity. ATMs
either swallow your card (really severe) or shut down
access until you go to your bank for a reset (almost as
severe). If you tried that for access in a corporation,
somebody's boss would come storming into your office,
probably the next day, wanting to know if you were trying
to shut the company down. Forcing an end to the attempt
followed by a 30-second break would be more acceptable
and would prevent any computer-generated attempt to try
all possible passwords.
By the way, comparing an encrypted attempt to an encrypted
password allows a nice little side effect, of rejecting a
password which is already in use, although you could have
a lot of trouble explaining to the dense that you really
don't have their password stored in plaintext somewhere.
The passwords "in use" would of course include many of the
really stupid ones like "PW" and "123456" and every word
in the Oxford English Dictionary. Many other
easily attacked ones can be excluded by insisting on a
lower case alphabetic, an upper case alphabetic, a digit
_and_ a special character (like "/" or the other stuff
your device will accept) somewhere in the password.
Oh yes, "a while" as you put it. A simple scheme like six
lowercase alphabetics would require over 300 million
tries, which at one a second if you're a demon typist
or thumber would take something of the order of twelve
years; but take heart, you'd have an even chance of
success in the first six years. If my arithmetic is
correct.