666
7 Countermeasures Against Hardware Trojans
unconditional transmission to the vector address, which is set in advance and corresponds to the relevant program of interrupt processing. In this case, in the interrupt processing program, the CPU uses a special interrupt handling program corresponding to the detection signal. For example, immediate actions taken may include
promptly informing users or the main system about the detection of the activation of
the main malicious modes of SoC and the system as a whole.
Depending on the competence of the user, purpose of the attacked system (a
missile base or a trout breeding farm), the CPU can generate a special reset signal
to the Trojan IP block in order to purposefully reset all registers inside such infected
block, enable strobing of the corresponding clock signal to this block in order to stop
the activated Trojan as quickly as possible or to enable the power strobing signal
to this block, turning off power immediately or in sequence for each element of the
Trojan block.
Figure 7.8 shows the structural diagram of a standard one-chip system with power
strobing.
The structure of the power switching block includes a special standardized VDD
cell for this functional block with power strobing. It helps isolate the entire charged
functional block from all power sources by using a standard power strobing controller.
When this block goes to the state with power strobing, all output signals of this block
shall be only linked to Vdd or GND. Otherwise, the block receiving signals as input
System bus
Functional IP core
with forced strobing
Functional block
without strobing
Power supply design
Isolated connecting
logic circuits
Controller of common
forced system strobing
Strobed
Acknowledgment
(confirmation) of the
functional signal
Signal of the
controller with forced
strobing
Fig. 7.8 Simplified structure of a system on chip with power strobing mode [29]
7 Countermeasures Against Hardware Trojans
unconditional transmission to the vector address, which is set in advance and corresponds to the relevant program of interrupt processing. In this case, in the interrupt processing program, the CPU uses a special interrupt handling program corresponding to the detection signal. For example, immediate actions taken may include
promptly informing users or the main system about the detection of the activation of
the main malicious modes of SoC and the system as a whole.
Depending on the competence of the user, purpose of the attacked system (a
missile base or a trout breeding farm), the CPU can generate a special reset signal
to the Trojan IP block in order to purposefully reset all registers inside such infected
block, enable strobing of the corresponding clock signal to this block in order to stop
the activated Trojan as quickly as possible or to enable the power strobing signal
to this block, turning off power immediately or in sequence for each element of the
Trojan block.
Figure 7.8 shows the structural diagram of a standard one-chip system with power
strobing.
The structure of the power switching block includes a special standardized VDD
cell for this functional block with power strobing. It helps isolate the entire charged
functional block from all power sources by using a standard power strobing controller.
When this block goes to the state with power strobing, all output signals of this block
shall be only linked to Vdd or GND. Otherwise, the block receiving signals as input
System bus
Functional IP core
with forced strobing
Functional block
without strobing
Power supply design
Isolated connecting
logic circuits
Controller of common
forced system strobing
Strobed
Acknowledgment
(confirmation) of the
functional signal
Signal of the
controller with forced
strobing
Fig. 7.8 Simplified structure of a system on chip with power strobing mode [29]