Password Cracking

Many passwords are necessary to live in the modern society. How many passwords do you use? They are cash cards, credit cards, PC and many secured web sites. Do you use secured passwords for them? Secured passwords are usually hard to memorize.. And so, it's  a trend to reduce the number of the passwords such as OpenID. If a site joins into OpenID, you could use your ID to other sites which join into OpenID. If many sites join into OpenID, you will memorize less IDs and passwords. Finally, you will use more secured passwords. However, if the password was cracked, your all sites would be attacked...
This book doesn't tell how to crack passwords, but you could learn password basics and how to use cracking tools.