344
4 Hardware Trojans in Microcircuits
corresponds to a signal-to-noise ratio of 10 dB, the size of the minimum detectable
Trojan increases to seven logical elements.
4.6.2.10 Method of Localizing a Trojan in a Microcircuit
Researcher Salmani et al. [182] used special scan chains to increase the probability
of detecting hardware Trojans. The device they intended to use for testing integrated circuits is usually not related to a particular microcircuit design. The approach
involves the use of a circuit with the location of scan chains over the entire area of
a microcircuit, so that specific areas can be specifically activated (or deactivated)
during functional testing.
This should lead to the detection of signs of Trojan activity. It is shown that
experimental trials demonstrate a partial increase in the activity of Trojans by a
factor of 30
4.6.2.11 Improved Characterization of Logical Elements
The method for detecting Trojans by combining characterization of logical elements
with thermal conditioning is presented in work [182]. Thermal conditioning means
that the information system is specifically heated in an uneven manner. This method
is based on the physical effect that the leakage current increases exponentially with
increasing temperature.
The objective of this method is to exclude other correlations that arise in the
process of measuring the magnitude of leakage current and are caused by the interdependence of logical elements. Due to the uneven heating of interconnected elements,
the calculation results become more variable. The results of such a simulation can be
used to calibrate the measurement procedure itself and to minimize the differences
in measurement results caused by manufacturing tolerances in the process of making
an IC. The advantage of using this method is a complete characterization of all the
logical elements of an information system.
The method for detecting Trojans by combining characterization of logical
elements with thermal conditioning is not suitable for microcircuits with a large
area, since the properties in this case are determined for the entire circuit. Highly
professional attackers can take advantage of this fact and install extremely smallsized Trojans, the effect of which will be unnoticeable against measurement interferences [187]. In order to make this process customizable and, therefore, suitable for
analyzing large information systems, Wei and Potcognac [187] expanded the process
by adding a preliminary segmentation step that allows breaking down a large circuit
into many smaller elements.
Segmentation criteria are chosen in such a way so as to ensure maximum accuracy of the results of subsequent characterization. The segmentation process itself is
achieved by changing the number of initial input vectors and simultaneously freezing
other input vectors. The part of a circuit obtained by segmentation in this case is
4 Hardware Trojans in Microcircuits
corresponds to a signal-to-noise ratio of 10 dB, the size of the minimum detectable
Trojan increases to seven logical elements.
4.6.2.10 Method of Localizing a Trojan in a Microcircuit
Researcher Salmani et al. [182] used special scan chains to increase the probability
of detecting hardware Trojans. The device they intended to use for testing integrated circuits is usually not related to a particular microcircuit design. The approach
involves the use of a circuit with the location of scan chains over the entire area of
a microcircuit, so that specific areas can be specifically activated (or deactivated)
during functional testing.
This should lead to the detection of signs of Trojan activity. It is shown that
experimental trials demonstrate a partial increase in the activity of Trojans by a
factor of 30
4.6.2.11 Improved Characterization of Logical Elements
The method for detecting Trojans by combining characterization of logical elements
with thermal conditioning is presented in work [182]. Thermal conditioning means
that the information system is specifically heated in an uneven manner. This method
is based on the physical effect that the leakage current increases exponentially with
increasing temperature.
The objective of this method is to exclude other correlations that arise in the
process of measuring the magnitude of leakage current and are caused by the interdependence of logical elements. Due to the uneven heating of interconnected elements,
the calculation results become more variable. The results of such a simulation can be
used to calibrate the measurement procedure itself and to minimize the differences
in measurement results caused by manufacturing tolerances in the process of making
an IC. The advantage of using this method is a complete characterization of all the
logical elements of an information system.
The method for detecting Trojans by combining characterization of logical
elements with thermal conditioning is not suitable for microcircuits with a large
area, since the properties in this case are determined for the entire circuit. Highly
professional attackers can take advantage of this fact and install extremely smallsized Trojans, the effect of which will be unnoticeable against measurement interferences [187]. In order to make this process customizable and, therefore, suitable for
analyzing large information systems, Wei and Potcognac [187] expanded the process
by adding a preliminary segmentation step that allows breaking down a large circuit
into many smaller elements.
Segmentation criteria are chosen in such a way so as to ensure maximum accuracy of the results of subsequent characterization. The segmentation process itself is
achieved by changing the number of initial input vectors and simultaneously freezing
other input vectors. The part of a circuit obtained by segmentation in this case is