Speciální p?íru?ka NIST 800-63 k elektronické autentizaci i password?m, 50 stran01.11.2004
...But how strong is strong enough for a very strong password? Help is available—and you've already paid for it. The National Institute of Standards and Technology has just released a new guide to selecting passwords, covering the four levels of protection necessary, guidelines on how to tell how strong a password is, and how to create a stronger password.
The NIST document is 50 pages. If that's more than you want to know about password's—or if you're looking for something fast to hand out to your users—NIST provides a guide to password creation and checklist to make sure passwords comply with your policies.