156.28 is a USA security rating from the Builder's Hardware Manufacturing Association (BHMA) and American National Standards Institute (ANSI) that defines the standards for master keying systems. 156.28 is one of the few BHMA/ANSI standards that is freely available.
- Change key
- A key that opens one lock or a group of keyed-alike locks in a given keying system.
- Concealed key control
- The requirement that all locks be marked with a standard symbol in a concealed location when the lock is installed.
- Control key
- A key that can remove or install a lock cylinder.
- Declining step key
- A key with a staircase style bitting pattern; descending towards the tip.
- Incidental master key
- A key that has a bitting capable of acting like a master key though it was not designed as a master key. (The standard text calls this an "unplanned shear line".)
- Keying conference
- A meeting between the end user and the key system designer where specifics of the key system are decided upon.
- Visual key control (VKC)
- The specification that keys and locks must be marked with standard keying symbols.
A keying conference is held to determine system requirements and design parameters. All doors are assigned a unique identifier prior to the meeting. Identifiers are used during planning, installation, and maintenance of the system. Large systems may include floor plans, blueprints, and other helpful information.
Objectives of the keying conference:
- Determine level of key restriction.
- Identify key system administrators.
- Identify the scope of the key system.
- Identify the growth of the key system and the need for future expansion.
- Determine who will service the keying system.
- Determine the levels of keying and total number of key systems needed.
- Determine requirements of service, lock/key technology used, and any special functions.
Systems are developed with the user's preferences and requirements in mind. Generic or third-party systems should not be used.
- Top master keys (TMKs) should have a bitting that resists premature removal from the cylinder and lockpicking. Declining step bittings should not be used.
- TMKs should contain the shallowest possible cut to mitigate the possibility of a lower privilege key being modified into the TMK. When possible, the TMK should also contain one of the deepest possible cuts.
- System administrators will take all possible measures to ensure the TMK is not duplicated in a given geographical area. When multiplex keyways are used, their relationship must be considered during the TMK issuing process.
- Keyway profiles must be selected based on the amount of key control and system expansion required by the end user.
- The choice of master key progression should minimize the number of incidental master keys. Ideally, proper progression leaves no duplicate key bittings or key interchange. Random key bittings must never be used.
- All products must be labeled to indicate their relationship to doors and keysets in the system.
Keying systems must be maintained properly to ensure their effectiveness. The following points facilitate an effective and secure key system:
- If returned keys should not be destroyed they should be kept in a lockable enclosure.
- If returned keys should be destroyed the key system adminitrators should develop a procedure for properly destroying keys.
- All issued keys should have records which indicate:
- Key holder
- Opening ("history of door location")
- Keyset to key holder
- Keyset to opening
- Key cabinet position (if applicable)
- No keys should be issued without written consent.
- Key issues should be minimal, with only one person in charge of this task with one backup available.
- Changes to the system must use bitting patterns consistent with a given progression method.
- Only manufacturer approved components should be used to assemble/maintain locks.
- Personnel who key locks should be technically competent.
- Code-based key machines should be used to generate keys.
- All key machines should use manafacturer approves parts and related tools.
- Key machines must conform to manufacturer specified key bitting tolerances.
- An inventory of key bittings and lock specifics should be maintained for emergency situations.
- Information about key bittings and lock combinations should be kept secure.