Key Control: Limiting Who Can Get a Key

Layers of Key Control

Key control is built from several separate measures, and they work together:

• Restricting the blank. If uncut key blanks are hard to get, unauthorized copies are hard to make. LIST defines a restricted keyway as one "whose sale and/or distribution is limited by the lock manufacturer in order to reduce unauthorized key proliferation."
• Legal protection. Patents or other legal rights let the manufacturer act against unauthorized blanks.
• Authorization procedures. Duplicates are cut only after a signature, card, or letter is verified.
• Records and management. These track who holds which key and what each key opens.

Restricted and Proprietary Keyways

A proprietary keyway, in LIST's terms, is "assigned exclusively to one end user by the lock manufacturer. It may also be protected by law from duplication." Manufacturers sell restricted keyways at different levels of exclusivity. Schlage's key-systems guide lists tiers including:

• "End user exclusive nationwide"
• "End user exclusive within time zone/country" and "within zip code"
• "Dealer exclusive" by region
• "Authorized dealer only; non-exclusive"

It contrasts these with its open Classic keyway, which is marked "duplicate anywhere."

See restricted keyways and key blanks and keyways.

Patents as Legal Control

Many high-security key systems rely on patents. In the U.S., a utility patent's term ends "20 years from the date on which the application for the patent was filed" (35 U.S.C. § 154). Design patents run 15 years from grant (35 U.S.C. § 173). Because patent terms are fixed, the patent-based part of a system's key control has an end date. Manufacturers publish these dates:

• Medeco. Its 2025 catalog lists patent expirations of 2040 for M4, 2030 for X4, 2021 for Medeco3, 2005 for Biaxial, and 1985 for the original system. It recommends upgrading from the expired systems.
• Schlage. It markets its Everest 29 keyway with "patent protection to 2029."

Medeco explains the reasoning: "Anyone with even temporary access to original keys has no problem getting duplicates made for their own use if the keys and key blanks are not patent protected." It also says it uses "special key cutting machines" that "are not found at general hardware stores," and that every restricted blank "is custom coined and tracked." See Medeco and high-security locks.

"Do Not Duplicate" Stamps

A key stamped "Do Not Duplicate" signals what the owner wants. Whether that stamp has legal force depends on where you are.

Medeco's catalog takes the cautious view: "Even stamping 'Do Not Duplicate' on a key merely warns someone not to copy the key – it is not a promise of legal protection or enforcement. The only way to ensure that keys cannot be copied without the consent of the owner is a key system with patent-protected keys."

At least one state goes further. California Business and Professions Code § 6980.54, effective January 1, 2009, prohibits licensed locksmiths from duplicating a key that is stamped "Do Not Duplicate" or "Unlawful To Duplicate" and carries the originator's company name and telephone number. It also covers a restricted or high-security key that carries the originator's name and telephone number or registration number. Rules in other states were not reviewed for this article.

Authorization Programs

Manufacturers run programs that decide who may order or cut keys. Medeco's catalog describes several:

• Signature card on file. The owner signs a card kept by the original security provider. Duplicates come from that provider after verification.
• Card programs. Authorized people carry a card with "embossed control data and a space for their signature." Any participating dealer can verify it.
• End user program. Facilities with their own locksmith produce their own keys.
• Factory program. "Additional keys are only available from the Medeco factory and only with the proper signature."
• Commercial program. This is for users who want physical security only. Keys "may be obtained from any Medeco locksmith without specific authorization."

The last program shows that a high-security cylinder does not automatically come with key control. It depends on the program the owner chooses.

Standards: ANSI/BHMA A156.30

ANSI/BHMA A156.30, High Security Cylinders, includes key control as a graded feature. Its 2014 text says this "is intended to provide security by limiting the availability of unauthorized keys or unauthorized electronic credentials that would operate the locks." The 2014 edition describes three levels, each building on the one before:

• Level C. Blanks are available only from the manufacturer, not from a second source. Manufacturers maintain internal procedures to protect keys.
• Level B. Level C, plus "blanks are protected by law."
• Level A. Level B, plus "factory cut keys are only provided by the manufacturer only after authorization."

Parallel requirements cover electronic credentials, from proprietary encoding up to factory-programmed credentials or dynamic authorization. The standard also bars visual key control marking on high-security cylinders. It prohibits printing bitting or credential serial numbers directly on credentials.

The current edition is A156.30-2025. BHMA's summary describes its levels as increasingly protective, with "level 'C' being the highest," which is the reverse of the ordering implied by the 2014 key-control table. Readers should check the edition in force for letter meanings.

UL 437 focuses on physical attack resistance. A 2007 DEF CON presentation by Marc Weber Tobias and Matt Fiddler summarized it as having "no key control criteria." See UL 437.

Records and Key Management

The second LIST sense of key control is record-keeping. Key records typically include the bitting list, key bitting array, key system schematic, end user, number of keys and cylinders issued, names of key holders, and the keying schedule. LIST defines a key cabinet as one "designed to store keys systematically." LIST also distinguishes a blind code, which is "unrelated to the bitting," from a direct code, which "includes the actual combination of the key."

In Europe, EN 1303:2026 points to CEN/TS 17814 for "protection of data and sensitive information related to mechanical Master Key Systems." See EN 1303, master keying, and construction keying.

Related Topics

• Restricted keyways
• High-security locks
• Medeco
• Master keying
• Key blanks and keyways
• Key cutting
• Key bitting
• Interchangeable cores
• Rekeying locks
• UL 437
• EN 1303
• Access control
• RFID locks
• Construction keying

Sources