Wednesday, April 9, 2008

Enforcing Passwords Security

It might not seem like an important thing to mention at this point, but you need to enforce a policy that makes users choose good passwords. And when you do that, you must decide what makes a good password for your environment. Simply put, a good password is one that is hard to guess. When you consider that a standard password-cracking technique used by hackers is to simply try every word in a dictionary, you can begin to understand that luck doesn't have a lot to do with penetrating a network. It comes mostly from lax security that allows doors that are easy to open.

Enforcing Good Passwords

When deciding how passwords are to be constructed, there are a few guidelines you can follow:

  • Use more than one word. Multiple words "glued" together make a pattern of characters t is much harder for a simple password-cracking program to guess. Don't use words that natur go together. For example, Atlantabraves is not a good choice; Atlantayoko is a better choice. Never use a name of a celebrity or a popular institution.
  • In Unix and Windows NT/2000/Server 2003 Server editions as well as Windows XP, passwords are case sensitive. If you use both upper- and lowercase characters in a p word, you can confound many password-guessing applications. Do not, however, substitute numeric characters that resemble alphabetic characters. One of the easiest things a password- hacker application can do is to substitute the letter "0" for zero. Don't fall for that one!
  • Don't make passwords too difficult to memorize. The last thing you want is to have frustrated users writing down passwords so that they will be able to remember them. If you this happening, it's time to re-educate the employee. There are many methods in use today t can be used to provide "one password" for all applications on the network. You should inves gate these types of applications and, if appropriate for your network, justify the cost versus t cost of a network intrusion. Many of these systems involve smart cards and PIN numbers. Again, although this may be an expensive up-front cost, justify it by the value of your data.
  • Use password history restrictions if the operating system permits it. This means the operating system keeps track of a limited number of passwords that the user has previou used and will not allow them to be reused within a certain time frame. A common practice is change your password when forced to do so and then to change it back to a value that you like and can easily remember.

Be sure that you do not create user accounts and assign them a password that never gets changed by the user. Most operating systems will allow you to set a password to be expired on its first use so that when a new user logs in the first time, he will be ruired to change his password.

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Sometimes it is important to have a password that makes no sense whatsoever. In a highly secure environment this can make sense, in that you want something that is hard to guess. However, remember that when something is difficult to remember it usually gets written down somewhere, which can defeat the purpose of a password altogether. Unix has a command, passwd, that can be used to computer-generate a password for a user. For example, the command


displays a list of potential passwords that are generally difficult to guess. The user can select one from this list to use if he is having a difficult time thinking one up. The only problem with this method is in getting the user to memorize the password.

Password Policies

No user account, including one used by an administrator (or root for the Unix/Linux community), should ever be allowed to keep the same password for an extended period. A good idea for passwords is to require that they be changed every 30-60 days, depending on the level of security you need at your site. You also should enforce a minimum length for passwords. Most operating systems willallow you to specify this value so that users cannot change their password to one that is shorter than the size you require.

On Unix systems, you can set the password minimum length by specifying it in a field in the file /etc/default/passwd.

On Novell NetWare servers, you can enforce a minimum password length by modifying the object properties of the template object used to create a user account, or by modifying the properties of an individual user object for a particular user.

Depending on the particular operating system, you can enforce other restrictions on passwords or user accounts to enhance security on the network. Some of the capabilities you might find include these:

  • Password expirations—A password should not be used indefinitely.
  • Password history lists—This feature prevents a password from being reused within a specified period.
  • Account lockouts—When a hacker is trying to use the brute-force method to guess a password for an account, you should be able to lock out the account automatically after a specified number of attempts within a specific time frame.


About the oldest trick known to those who would want to break into another user's account is the use of a program that imitates the operating system's own logon procedure. This kind of program generally is executed by someone who logs in using his own account on another's workstation. He thenruns a program that does nothing but wait until the unsuspecting user tries to log in. The program prompts for a username and password, mimicking the operating system in every respect. However, instead of logging the user on to the system, which the program is unable to do, it simply stores the password in a file and then generates a phony error message.

If the user is not too concerned about security, he will probably never know that he has been fooled. The user might think he has entered his password incorrectly and try again. The second time it will succeed because it is the operating system that is prompting the user this second time. The password grabber program has already done its job and it disappears.

The user who began this fraud simply retrieves the file, thus getting the password, and then can freely log in as that user and cause many problems when it comes to tracking down the real person who is abusing security. Because the perpetrator is now using someone else's username and password, he is difficult to catch.

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