656
7 Countermeasures Against Hardware Trojans
If the method is used on the command level, the activity on this level can be
transparent for higher levels of the TSB, on which it is possible to verify the command
level of schedules, selection of replication blocks, setting of different variants and
voting.
Rigid configuration of the two-processor architecture with direct communications, which is an implementation of replication and voting at the macro level, is
suggested in [21]. Both process receive and process the same instructions simultaneously. Hardware-implemented logic checks and compares all controlling signals of
every transaction on the bus. If a mistake is found, the system is forced into the error
recovery mode. In order to adequately protect the system from hardware Trojans,
complete verification of TSB blocks for checking and eliminating errors should be
carried out. This method can be extended for a larger number of processors, which
can be separated ICs or be included in a single FPGA.
As early as in 1991, the work [25] examined the issues of ensuring high reliability
and operability, as well as preserving data confidentiality in large-scale distributed
systems. Threats associated with hardware Trojans were not examined; however,
the suggested methods of failure safety are still relevant today for counteracting
unauthorized implants. General approach suggests dividing data into small fragment,
each fragment containing only a small amount of information. It can be used for data
storage or processing (accordingly, they are grouped as fragments for storage and
processing). Replication of fragments is used to increase reliability of the system.
Threshold circuits similar to secret exchange circuits (such as [26]) are suggested
for rearrangement of stored and processed data. At the same time, determination
of functions of general purpose fragmentation is a fairly complex and expensive
computing process. Such mechanism can be implemented in the form of computing
elements on discrete hardware means. In this case, the required TSB includes inputs
and outputs of storage and processing of operations.
There is currently no universal solution that would ensure complete protection
from the entire spectrum of threats and mechanisms of activation of hardware Trojans
during operation of the system. It is unlikely that such solution will ever be found.
In turn, combinations of countermeasures are required to combat specific classes
of hardware Trojans in specific application fields. These countermeasures shall be
designed considering specific systems in which they will be applied, as well as
considering the provided level of protection. As demonstrated in works [2–12, 14,
27, 28], during development of any new countermeasures, the methods to bypass
them emerge naturally. This arms race in the field of hardware Trojans dictates the
necessity of using complex “deeply staggered” approaches to ensuring hardware
security of modern electronic systems.
7 Countermeasures Against Hardware Trojans
If the method is used on the command level, the activity on this level can be
transparent for higher levels of the TSB, on which it is possible to verify the command
level of schedules, selection of replication blocks, setting of different variants and
voting.
Rigid configuration of the two-processor architecture with direct communications, which is an implementation of replication and voting at the macro level, is
suggested in [21]. Both process receive and process the same instructions simultaneously. Hardware-implemented logic checks and compares all controlling signals of
every transaction on the bus. If a mistake is found, the system is forced into the error
recovery mode. In order to adequately protect the system from hardware Trojans,
complete verification of TSB blocks for checking and eliminating errors should be
carried out. This method can be extended for a larger number of processors, which
can be separated ICs or be included in a single FPGA.
As early as in 1991, the work [25] examined the issues of ensuring high reliability
and operability, as well as preserving data confidentiality in large-scale distributed
systems. Threats associated with hardware Trojans were not examined; however,
the suggested methods of failure safety are still relevant today for counteracting
unauthorized implants. General approach suggests dividing data into small fragment,
each fragment containing only a small amount of information. It can be used for data
storage or processing (accordingly, they are grouped as fragments for storage and
processing). Replication of fragments is used to increase reliability of the system.
Threshold circuits similar to secret exchange circuits (such as [26]) are suggested
for rearrangement of stored and processed data. At the same time, determination
of functions of general purpose fragmentation is a fairly complex and expensive
computing process. Such mechanism can be implemented in the form of computing
elements on discrete hardware means. In this case, the required TSB includes inputs
and outputs of storage and processing of operations.
There is currently no universal solution that would ensure complete protection
from the entire spectrum of threats and mechanisms of activation of hardware Trojans
during operation of the system. It is unlikely that such solution will ever be found.
In turn, combinations of countermeasures are required to combat specific classes
of hardware Trojans in specific application fields. These countermeasures shall be
designed considering specific systems in which they will be applied, as well as
considering the provided level of protection. As demonstrated in works [2–12, 14,
27, 28], during development of any new countermeasures, the methods to bypass
them emerge naturally. This arms race in the field of hardware Trojans dictates the
necessity of using complex “deeply staggered” approaches to ensuring hardware
security of modern electronic systems.