This article discusses the probability of random code or key factor in lock quality, a crucial factor for all lock de
Probability: The Key Factor in Lock Quality
Understanding the Key Factor in Lock Quality
The Importance of Probability in Lock Quality
This article discusses the probability of random code or key duplication in locks, a crucial factor for all lock designs and a key factor in lock quality.
The History and Evolution of Mechanical Locks
First, with mechanical key locks, these locks originated in ancient Egypt about 6000 years ago. Wooden versions with gravity-operated pins have been found, as shown in Figure 1, with their operation explained in Figure 2.
Figure 1: Ancient Wooden Lock
Figure 2: Longitudinal Section of a Lock with Gravity-Operated Pins
Key Duplication Probability Explained
To understand what makes a lock secure, we must consider the probability of code or key duplication. Take the ABUS lock, model 75IB/60 Marine, which the company states has a key duplication rate of 1/168,000. This means that during manufacturing, the key-cutting machine is programmed so that the first key set differs from the second and only repeats the data cycle after 168,000 sets. Thus, if a market imports a batch of 168,000 locks, no two locks will share the same key.
Enhancing Lock Security Through Design
Increasing Key Duplication Probability for Improved Lock Quality
For engineers, a higher probability of key duplication requires more factors to be included in the encoding. These factors can be the number of grooved sides, the number of grooves on one side, groove shape, groove width, tooth shape, lift of each tooth, the number of pins, etc. The combination of all these factors results in the probability of key duplication. From a design perspective, to increase the difficulty of random code guessing and enhance lock quality, more encoding factors should be added, such as the crown lock increasing the number of key grooves to eight for this purpose.
Figure 3: Various Lock Cores with Different Numbers of Grooves
Combination Locks and Their Impact on Lock Quality
Regarding combination locks typically used for luggage or common padlocks, these locks do not require carrying a key, and the lock code is a set of three or four numbers chosen during setup.
Figure 4: Combination Lock
The probability of a combination lock depends on the number of code wheels, typically not exceeding 4-6 in practical conditions. The probability also depends on the number of digits on each code wheel, usually limited to 0-9. The quality of this lock depends less on probability and more on mechanical workmanship. If the code wheels have minimal play, the lock is easy to pick, so the focus of security efforts should be on mechanical workmanship to ensure high lock quality.
Advanced Lock Mechanisms and Security
Enhancing Front-Drive Disc Locks to Improve Lock Quality
For front-drive disc locks typically used in purely mechanical safes, their structure is shown in Figure 5.
Figure 5: Front-Drive Disc Lock in a Combination Code
To increase the probability of random code guessing and improve lock quality, more discs can be added. When the number of discs increases, the number of turns needed to open the lock increases significantly. For example, if there are currently four discs, the number of turns required to open it is 4+3+2+1=10 turns. Adding one more disc would increase the turns to 15, which is impractical as it takes too much time while maintaining the same principle. Another way is to increase the number of marks on the dial; instead of 100 marks, it could be 120. However, the dial size is limited, and increasing the marks makes them too dense and hard to read. Moreover, the precision of the groove machining and their relative positioning needs to be much higher, making the operation more precise to reduce play, which is not practical for all users. Locksmiths do not pick all combinations theoretically but use even-odd elimination principles, such as the final number being between 20 and 90, to avoid displacing correctly set rings. Combining this with a stethoscope, only a few cases need verification, bypassing theoretical combinations. This is why locksmiths often pick combinations manually rather than using CNC machines, as experience eliminates known variables.
Electronic and Biometric Locks: Modern Security Challenges
The Complexity of Electronic Keypad Locks and Their Impact on Lock Quality
For electronic combination locks using a numeric keypad, the code length is determined by software, not hardware, making the theoretical probability very high. It’s important to understand that the final execution stage of these locks is usually a solenoid, which creates a magnetic force to move the core in the coil when an electric signal is applied. The structure of a solenoid is shown in Figure 6.
Figure 6: Commercial Coil and Solenoid
Overcoming Security Challenges to Enhance Electronic Lock Quality
The question is whether electronic keypad locks are safe given their high theoretical probability. The answer lies in understanding that a lock’s full operation involves three stages: receiving the user-entered code on the keypad, transmitting it to the microcontroller, and the microcontroller comparing and deciding to power the solenoid. Attacks on the system usually target stages beyond finding the entered code.
An attacker won’t try to recreate the code from the keypad due to its low probability but will attempt to directly shock the solenoid. As shown in Figure 7, the solenoid is a coil that generates electricity when exposed to a changing magnetic field, as per Faraday’s law. Typically, the coil needs to be powered to operate, but moving a powerful rare-earth magnet close to it can create a similar effect, opening the lock without needing the entered code.
Addressing Security in Biometric Locks to Maintain High Lock Quality
Similarly, for fingerprint locks, creating a biometric signal has a very high probability, but the subsequent stages are the weak points. The execution and microcontroller stages can be shocked to auto-open or reboot, creating security holes. As a customer, you should not only focus on the signal creation method—whether a card, fingerprint, or keypad—but also on how the microcontroller and execution stages are protected from becoming a weak link. These issues do not apply to the purely mechanical locks mentioned above.
Conclusion: Ensuring High Lock Quality Through Continuous Improvement
Understanding the probability of key duplication and addressing potential security challenges in both mechanical and electronic locks is crucial for ensuring high lock quality. By focusing on innovative designs, precise mechanical workmanship, and robust electronic security measures, manufacturers can create locks that offer superior protection and reliability.
