Character classes: For the purposes of authentication and password complexity, there are four possible character classes:
- Upper case alphabetic (e.g. A-Z)
- Lower case alphabetic (e.g. a-z)
- Numeric (e.g. 0-9)
- Special characters (e.g.!@#$%~).
A password with all four character classes might be: "Always b3 Secure."
- it has upper case alphabetic: "A" and "S"
- it has lower case alphabetic: "always b ecure"
- it has a number: "3"
- it has a special character: "." (period)