Understanding Hardware Trojans and Their Potential Damage
Hardware trojans have become a growing concern in recent years. While many people associate hardware trojans with network cards, it is important to understand that they can cause real damage beyond just the network card.
One might wonder why hardware trojans are such a threat. After all, if a server or computer is compromised, why not just focus on the network card as the potential source of the trojan? However, it is essential to note that a perfectly honest network card acts under the control of the host CPU. This means that a malicious hardware element in the CPU can betray the user’s secrets, even if the trojan is not directly targeting the network card.
Any piece of hardware with DMA (Direct Memory Access) access has the ability to read and write memory at will. This means that it can modify the operating system and application code as it is executed. In other words, it can perform actions similar to kernel-level malware, which can be incredibly harmful. This includes not only the CPU itself but also the GPU, hard disk controllers, network cards, and USB controllers.
Even if you are considering a dormant backdoor, which only becomes active when triggered from the outside, it can still be implemented purely in the CPU or the DMA controller. By having the CPU or the DMA controller inspect memory transfers and wait for a specific pattern, the hostile code can be activated. For example, a specific pattern in a ping request or other packet can be used to trigger the dormant backdoor. The DMA controller will identify the pattern when transferring the packet from the network card to the main RAM, and the CPU will detect it when recomputing the IP packet checksum.
The reason people are afraid of hardware backdoors is the lack of control. Unlike software, which can be monitored and controlled to some extent, hardware backdoors are difficult to detect and mitigate. Once a hardware backdoor is present, individuals have little control over its actions and the potential damage it can cause.