Introduction to Uniform Strength Theory
The uniform strength theory posits that in a structure, when components work together, they should have equivalent strength. The goal is for components to fail simultaneously at the end of their life cycle, prompting the user to switch to a new product. This approach is economically sound, ensuring that no component is unnecessarily robust or expensive while maintaining overall performance.
Mechanical Aspects of Safe Design
Evaluating Safe Door Bolts
When considering a safe, especially common models, there are many discrepancies in both mechanical and electronic aspects. First, let’s examine a crucial mechanical element of the safe: the door bolt, which can be hollow (Figure 1.a) or solid (Figure 1.b).
Figure 1: Hollow Bolt (left) and Solid Bolt (right)
The bolt resists mechanical impacts during an attack with hand tools such as hammers, crowbars, and chisels. However, it doesn’t resist the attack alone; it must rely on the door. The force applied to the bolt transfers to the door and frame, and if any link in this chain fails, the safe’s protection ceases.
Misleading Commercial Practices
Most safes on the market emphasize the number and diameter of the bolts. This is visually convincing for customers who may not fully understand the issue. A large-diameter bolt array creates a sense of safety, but the reality is different.
Consider the scenario shown in Figure 1.a after an attack. The hollow bolts, with a diameter of no more than 20mm, did not deform, while the 0.8mm folded sheet metal door was completely destroyed. Customers only realize then that reinforcing the shell is more significant than increasing the number or diameter of bolts. There is no uniform strength between the shell and the bolts. According to our laboratory data, cutting a 20mm diameter steel bolt requires 20 tons of force, as shown by SolidWorks simulations. To achieve uniform strength when prying with a crowbar from the door edge, the sheet metal shell needs a minimum thickness of 6mm, provided there is a reinforced box structure. Increasing the bolt diameter to 32mm, as in some designs, is purely for aesthetics.
Electronic Aspects of Safe Design
Assessing Electronic Lock Security
Consider safes that use numeric keypads or fingerprints for unlocking. From a probabilistic perspective, entering an 8-character code hidden within any length string seems extremely secure, and the same applies to fingerprints, as each person’s fingerprint is unique. Capacitive fingerprint sensors also require live epidermis and a heartbeat, making them impossible to fake. However, from a technical standpoint, obtaining the code by any method is very safe due to the improbability of faking such a signal. Real-world attacks occur at subsequent stages, not during the code entry phase.
Vulnerabilities in Signal Processing
The process of generating a control signal via fingerprint, numeric keypad, or card follows a common procedure: signal generation 🡺 transmission to the microcontroller for comparison with the sample 🡺 signal and energy output to the actuator to execute the unlock command. Attacks on the system typically occur at the middle or final stages.
Electronic locks generally have an actuator, either an electric motor (for rotational movement) or a solenoid (for linear movement). These actuators function when appropriately powered. There are two ways to affect them: electrically shocking the lock’s microcontroller, causing it to restart, which, if there is a software vulnerability, will lead to unlocking. Most cheap locks without anti-electric shock protection have this flaw, especially those of Chinese origin. The second method is magnetic shock, using a magnet near the solenoid coil, generating current in the coil as if it were powered, forcibly moving the lock blade.
Addressing Uniform Strength in Electronic Safes
Thus, uniform strength in the security levels of the stages is not well-maintained. Although signal generation using technologies like numeric keypads, fingerprints, or cards is excellent, resistance to shocks is a critical weakness of these lock systems that has not been addressed. Both methods mentioned, electrical shock and magnetic shock, show in some YouTube videos that they can be completed in under 10 seconds.
Conclusion
If you are a customer needing a professionally designed safe to counteract mixed threats, you should be aware of these issues. Ensuring uniform strength across all components, both mechanical and electronic, is crucial for optimal safe performance and security.
