Most z/VSE SubSystems, including CICS, VSE/POWER, VSE/ICCF, etc., internally use Fixed Length Fields, eg. 8 bytes for Userids and Password. Each SubSystem's Password Restrictions vary:
The native VSE Security Manager (BSM) currently supports IDs up to eight characters, and doesn't support Mixed Case. Because of these z/VSE Password limitations, Top Secret for z/VSE r3.0 is unable to support Mixed Case Passwords, Long Passwords and Password Phrases.