The dream of every lockmaker is to design an unpickable lock. Some of the most important advancements in lock design emerged from innovations by now-famous lockmakers during the 18th and 19th centuries. Recognising the commercial potential, and with opportunities transformed by industrial manufacturing, lockmakers from around the industrialised world sought to conceive and produce locks that were as difficult to pick as possible. In an age before power tools, greater emphasis was placed upon mitigating surreptitious and non-destructive attack methods, in contrast to the more common brute-force attacks using manual tools.

It was in these times of great commercial opportunity, innovation, and social change that brothers Theodor and Carl Kromer created their physical security company in western Prussia in 1868. They focused their attention on high-quality security locks for safes, vaults, and other secure containers. Kromer first patented their machine-made ‘Protector‘ safe lock in 1874 – in the same year that Joseph Glidden was granted his famous patent for barbed wire. A year earlier, Kromer had presented their Protector at the World Exhibition in Vienna, where it won the highest award available. Over the years, many other patents were added, relating to additional security features in response to potential vulnerabilities identified.

The Protector initially saw considerable commercial success within Prussia, specifically for high-security applications such as bank vaults, safes, and government secure containers, and was later exported to customers overseas. It quickly gained a reputation around the world for being an extremely difficult lock to breach, both non-destructively and destructively.

Technical Specifications of the Protector Lock

The Protector lock within The Security Museum Collection is of the later BP55K variant (a 1993 model), incorporating 16 wafers of varied dimensions. The design includes double-acting wafers that operate on both sides of the locking mechanism. Some wafers have cuts that interact with the key, while others serve purely deceptive purposes and do not affect operation. The number and design of the wafers constitute a key protection against lockpicking and decoding attacks, which aim to determine the internal wafer configuration to identify the required key. Crucially, the wafers must be lifted to an exact height for the lock to open.

The cylindrical core is constructed from thick steel with a drill-resistant plate integrated into its design. Very tight tolerances reflect the quality and precision-manufacturing standards employed, which Kromer were well known for. These tolerances themselves form part of the security as they make it very technically challenging to insert and effectively use lock picking tools. The design of the keyway, combined with two internal curtain plates, also makes manipulation very difficult. The keys, which turn approximately 45 degrees to unlock the mechanism and are retained, are double-bitted and asymmetrical, with some bits featuring grooves and angled cuts that interact with parts of the wafers. This sophisticated design provides around 234,256 possible combinations.

An added feature of this particular model is that it has been designed to work in conjunction with a permutation lock on a safe, for added complexity and security.

Other Kromer Security Products

Beyond the Protector, Kromer also produced other high-security safe locks, including the highly successful Novum (photo below) and the somewhat less commercially successful Integral, Reling, and Brisgovia models. Their product range also extended to mechanical and electric time locks as well as permutation locks. Nevertheless, Kromer remain best known for the Protector – a product of first class German security engineering.