Explanation
A minimum length requirement (as set on the Edit Authentication Rule page, in the Minimum Credential Length field)
* Inclusion of at least one character from each of the following categories: upper-case letter, lower-case letter, number, and symbol (~ ! @ # $ % ^ & * " ` , . : ; ? - _ ( ) [ ] < > { } + = / \ |)
* No characters repeated consecutively more than three times (for example, aaaaB1C9 is invalid)
* No inclusion of the alias or name of the administrator
Link: http://www.cisco.com/en/US/docs/voice_ip_comm/connection/8x/user_mac
/guide/8xcucmac070.html#wp1049964