DOCUMENT:Q102727  10-AUG-1993  [W_NT]
TITLE   :Password Uniqueness in Windows NT
PRODUCT :Windows NT
PROD/VER:3.10
OPER/SYS:WINDOWS
KEYWORDS:

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The information in this article applies to:
 - Microsoft Windows NT operating system version 3.1
 - Microsoft Windows NT Advanced Server version 3.1
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SUMMARY
=======
 
The Password Uniqueness parameter in Windows NT can confuse users.
There is no direct association between this value and the number of
passwords that a specific user has previously used.
 
MORE INFORMATION
================
 
Let's suppose that Password Uniqueness is set to 3. This does not mean
that at the third password change I can use an old password, or that
that after using three passwords I can use the first one again.
 
The Password Uniqueness parameter works as follows: 
 
   First password:  One                Passwords saved: <>
 
   First password change
     New password:  Two                Passwords saved: <One>
 
   Second password change
     New password:  Three              Passwords saved: <One,Two>
 
A user may think that the first password can be used again because
three passwords have been used. This is not true; the user must wait
until his password disappears from the saved password list. The next
password change will resemble the following:
 
   Third password change
     New password:  Four               Passwords saved: <One,Two,Three>
 
Some users may think that they can use their first password again,
because they've already changed their password three times. This is
incorrect also. The next password change will resemble the following: 
 
   Fourth password change
     New password:  Five               Passwords saved: <Two,Three,Four>
 
In the next (the fifth) password change, the user can use the first
password (One), because it is no longer on the list.
 
A better way to explain this is to regard the Password Uniqueness
number as the number (n) of entries in a fictitious table, where the
passwords in this table cannot be used. If you add to this your
current password, plus the new password that you will use, you get n+2
different passwords, and not n different passwords.
 
Be aware that if you want to keep n different passwords, Password
Uniqueness must be set to n-2. Be aware also that n can be any number
from 1 to 8.
 
Workaround
----------

If you mistakenly set up a number and you don't want that to be your
standard, you can change it, and the oldest entries from that table
will be removed so you can use those passwords.
 
To change Password Uniqueness:

1. From User Manager for Domains, select the Policies menu.

2. Choose Account.

3. Change your password uniqueness number in the Password Uniqueness
   box.

4. Choose OK.
 
Additional reference words: 3.10
KBCategory:
KBSubcategory: SCRTY

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