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Choosing Good Passwords -- A User Guide

This document presents a plain-language guide to help users understand how passwords are compromised and how to choose secure passwords.

The password management challenge

Passwords are used to protect various systems and services -- e-mail, PC and network logins, applications and more. Users must choose a password when setting up a new account and in many cases must periodically change that password.

Why change passwords?

The simplest thing to do is to have just one password on all systems and never change it. The problem with this strategy is that if any of those systems is compromised, then passwords on that system may be revealed. A password compromised on one system can be used to sign into another system where the same user has an account.

To mitigate this risk, it is reasonable to change passwords periodically and to use different passwords on different systems. Since it's hard to remember lots of different passwords, a reasonable compromise is to use just a few passwords -- for example, one for consumer services like Facebook or Google; another for e-Commerce web sites; another for personal banking and another for work.

Choosing hard to guess passwords

It's tempting to pick something trivial and easy to remember, like spelling your user name backwards, a child's name or a dictionary word. The problem is, the simpler the password, the easier it will be for an attacker to guess.

Attackers often gain access to systems by guessing or otherwise compromising a login ID and password. Having gained these credentials, an attacker can then impersonate a valid user.

If the attacker knows you, they can try password combinations related to your family, interests or history. If they have physical access to your desk, PC or phone, their chances of getting into your accounts are even greater, as your password may be written down or electronically stored, in plaintext, on one of these.

Attackers use readily available software to rapidly try plausible passwords, based on dictionary words and user names, until they hit on a valid password. If an attacker can get a copy of an encrypted password database, they can test billions of password guesses per second, to see if any are correct. At this pace, an attacker can guess many passwords in just a few hours.

The shorter and more predictable the password, the faster it can be guessed. Dictionary words spelled backwards, rearranged or with digits added are unsafe. Simple substitutions, such as replacing the letter l or i with the digit 1 are likewise unsafe, as password guessing software will try these.

Examples of bad passwords include:

  • mydog2
  • bi11smith
  • yromem (memory backwards)
  • win4me

The safest solution for choosing good passwords is to use a randomly generated or seemingly random password that:

  • Is at least 8 characters long.
  • Contains a mix of upper and lower case letters.
  • Includes digits and punctuation marks.
  • Is not based on any personal information.
  • Is not based on any dictionary word.

Examples of strong passwords include:

  • De2#vuX
  • 5sd$oiP
  • :er89TI:

Writing passwords

If you have too many passwords, it is tempting to write them down -- after all, can you really remember 10 different passwords, that change at different times, some of which are rarely used?

Writing down passwords is a serious breach of security, because it means that anyone who can physically get to the piece of paper, sticky note or phone that contains the password, can also log into systems with your accounts. Should a visiting vendor really be able to sign into the finance application? Should the janitor be able to read your e-mail?

A better solution is to create a single, strong password, and apply it to all of your login accounts. One password is easier to remember, and is more secure than a written note.

Reusing passwords

Another temptation, when imagination fails, is to reuse old password values when the time comes to change your password. This is also a security problem, since the whole point of a regular password change is to limit the time available to an attacker to crack your password. If an old password is reused, attackers will have more time to guess them. If the old password was already compromised, the new one will compromise your security again.

If you cannot think of a new, secure password -- have a program, like Hitachi ID Password Manager, randomly generate one for you.

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