Back to Basics: SiC Diodes

I had covered power electronic Silicon Carbide(SiC) MOSFETs earlier in my posts. Very recently, I had to work on a project that needed Silicon Carbide diodes. Then I really started to appreciate the benefits of it and more folks should start using them.

SiC diodes as the name suggests are based on the semiconductor material Silicon Carbide and have many benefits compared with traditional Silicon diodes. SiC diodes have wide bandgap properties, which allow them to handle higher voltages, temperatures, and switching frequencies than their silicon counterparts. SiC diodes exhibit much lower forward voltage drop, low reverse leakage current and switching losses, which means less energy is wasted in heat(energy reductions up to 50%). Means higher efficiency. SiC diodes can switch on and off much faster because they have practically very low/nil reverse recovery charge(Read more about them in older posts). This means they perform better in applications like high-frequency switching power supplies. It can handle junction temperatures exceeding 175°C (even up to 200°C in some cases), whereas silicon diodes tend to degrade at high temperatures. It has higher thermal dissipation capabilities and hence can be made smaller in size for similar Si devices
Because of all the benefits above, they are perfect for high voltage/high current applications in EVs, Inverters, and power supplies. They are relatively new. If you’re designing systems that demand high efficiency and high-temperature performance, SiC diodes are absolutely worth exploring, just as I did when I decided to take the leap with them.

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Advanced: RFID Backdoor Hack

Last month a hardware backdoor was published, which virtually comprises most RFID access-based systems out there. I haven’t been able to read it in detail till now. It’s a great read I have linked it below. RFID systems are used for access systems in hotel rooms and as employee badges use a cheap IC called FM11RF08. This is a contactless smart card chip developed by Shanghai Fudan Microelectronics, designed to be compatible with NXP’s MIFARE Classic cards but very cheap. Most devices in the last decade of installation would probably use this chip.

The paper reveals a critical flaw in FM11RF08S (newer secure version of the classic) cards. The vulnerability stems from a hardware backdoor, allowing attackers to access and compromise user-defined keys. This backdoor is triggered by using specific authentication commands that are normally used to initiate communication between the card and a reader. Through fuzzing (random testing of commands), they discovered that certain authentication commands respond in weird ways, allowing access to a backdoor authentication mechanism.

Normally, commands starting with 60 or 61 would authenticate using the card’s user-defined keys (keyA or keyB), but by changing specific bits, the card accepts a backdoor key, which allows the attacker to authenticate without knowledge of the actual keys. After breaking the backdoor key, the attacker gains access to all user-defined keys on the card, even if those keys are diversified or unique for each card sector. The allows an attacker to read all data stored on the card, including sensitive user information. Then the attacker can use a device like the Proxmark3 to clone the card. Once cloned, the attacker can emulate the card to any system that relies on the FM11RF08S. A pretty brilliant work with the hack.

So if you are a business owner using one of these systems and have something even remotely valuable guarding access with these chips, time to switch to something better!

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