Source | IoVSecurity

Editor | strongerHuang

Since the birth of MCUs in the 1970s, the technology for cracking chips and the solutions to prevent chip cracking have been in a continuous chase of “one height above the other”.

This article shares the development history of microcontrollers in security protection and summarizes the advantages and disadvantages of the highest security level smart card chips at the end of the article.

1. Single Board Computer Era

In the early 1970s, embedded systems were composed of separate components such as: CPU, ROM, RAM, I/O cache, serial ports, and other communication and control interfaces.

During this period, there were almost no protective measures, apart from legal ones, to prevent intruders from copying data from the ROM area on the single board computer.

With the development of large-scale integrated circuit technology, the central processing unit (CPU), data memory (RAM), program memory (ROM), and other I/O communication ports were integrated into a single microcontroller chip, replacing the single board computer. As shown:

As the number of intruders increased, MCUs added security fuses to prohibit data access for their own safety. As shown:

Later, MCU manufacturers made security fuses part of the memory array, as shown:

Using power-up to lock specific address areas as security fuses. Or using passwords to control memory access. For example, Texas Instruments’ MSP430F112 can only perform read-back operations after entering the correct 32-byte password. If not entered, only after erasing the byte password can read-back operations be performed. Although this protection method seems more effective than previous ones, it has some drawbacks that can be cracked using low-cost non-invasive attacks, such as timing analysis and power consumption. If the state of the security fuse is part of the memory after power-up or reset, it gives attackers the opportunity to use power noise to crack, forcing the route into an erroneous state in memory.

Using top metal layer designs increases the difficulty of intrusion. All grids are used to monitor short circuits and open circuits, and once triggered, it will cause the memory to reset or clear. As shown:

In recent years, some smart cards have used Bus Encryption technology to prevent probing attacks. As shown:

For developers, choosing a more secure design microcontroller can provide better protection. Compared to most microcontrollers, even smart cards designed ten years ago can offer better protection. Modern smart cards provide more anti-attack protections, internal voltage sensors protect against power noise attacks (Power Glitch attacks), over-voltage, and under-voltage protections. Clock frequency sensors prevent attacks that lower clock frequency due to static analysis. It can also prevent clock noise (Clock glitch attacks) that attempt to raise clock frequency. Top metal grids and internal bus hardware encryption can prevent micro-probing attacks. However, compared to microcontrollers, smart card chips also have disadvantages, such as high chip prices, and they are difficult to obtain in small quantities. Development tools are expensive, requiring confidentiality agreements with manufacturers, and even the manuals must be treated this way. Many manufacturers only sell large quantities of smart cards to specific customers. Another drawback is the limited I/O functionality; ordinary smart card chips usually only have ISO7816 interfaces, and very few have separate I/O ports. This makes them unable to replace microcontrollers in most applications and can only be used in industries with very high security requirements, such as: pay TV set-top boxes, bank cards, SIM cards, second-generation ID cards, high-end encryption chips, etc. The application of smart card chips in the field of encryption chips will be a good direction. Because smart card chips have high security levels, but fewer I/O resources. Meanwhile, ordinary MCUs have very rich hardware resources but low security levels, allowing some critical algorithms and operating parameters to be stored in special forms on smart card chips, thus achieving powerful functions with high security strength.

The ongoing struggle between groups attempting to break protective mechanisms and manufacturers continuously introducing new security measures is endless. “One height above the other” or “evil cannot suppress righteousness” will continue to play out between the two sides!