5.1 Brief Review of Basic Techniques for Detection …
465
5.1.17 Using Ring Oscillators for Detecting Trojans
Researchers Zhang and Tehranipur in work [51] use a network of regular ring oscillators to detect the presence of implemented Trojans. Such ring oscillator is a simple
circuit for generating oscillations, consisting of an odd number of similar elements
connected in series in the form of a ring.
The principle of detecting Trojans is based on the fact that physical parameters affect the frequency of the ring oscillator. Accordingly, the generator operating
frequency also depends on the supply voltage V. If the value V BD drops, the delay in
propagation of elements increases. This, in turn, means that the delay of the entire
ring oscillator and the duration (period) of its cycle increase, which is equivalent to
a drop in frequency.
A drop in the V BB value occurs if the element begins to consume current. If CMOS
technology is to be used, a drop occurs with each switch of the transistor, that is, in
each case of a change in its state. If a Trojan is installed in the circuit, adjacent ring
oscillators will register a more significant drop in V BB and frequency compared to
the parts of the microcircuit that do not contain Trojans.
In order to achieve the highest possible coverage, ring oscillators are installed over
the entire surface of the microcircuit. With the help of statistical methods used to
estimate frequencies of embedded ring oscillators, the probability of detection equal
to 100% is achieved. The efficiency of this approach in dealing with direct attacks
is considered fairly high, since the proposed manipulations have a direct impact on
the frequency of operation of ring oscillators, thereby revealing themselves when
performing corresponding functional tests.
This section presents a brief overview of the two methods of identification of
Trojans in microcircuits that were known at the moment of publication of this book.
However, the main problem currently is that none of these methods can guarantee
100% absence of a Trojan in the analyzed microcircuits.
Therefore, one of the most important tasks of developers of critical microcircuits is
development and unconditional compliance with the complexes of countermeasures
minimizing the possibility to introduce hardware Trojans into microcircuits during
any stage of its lifecycle, from design stages to organization of production and sales
through trusted supply channels.
5.1.18 Models of Multi-level Trojan Attacks
One of the types of a completely new class of cyberattacks—attack on cryptographic
algorithms—was first introduced by Ali et al. [3]. These so-called multi-level attacks
are based on the group interaction (synchronization of actions) of several individuals or even several professional teams of attackers involved in the development of
microcircuits and their production process.
465
5.1.17 Using Ring Oscillators for Detecting Trojans
Researchers Zhang and Tehranipur in work [51] use a network of regular ring oscillators to detect the presence of implemented Trojans. Such ring oscillator is a simple
circuit for generating oscillations, consisting of an odd number of similar elements
connected in series in the form of a ring.
The principle of detecting Trojans is based on the fact that physical parameters affect the frequency of the ring oscillator. Accordingly, the generator operating
frequency also depends on the supply voltage V. If the value V BD drops, the delay in
propagation of elements increases. This, in turn, means that the delay of the entire
ring oscillator and the duration (period) of its cycle increase, which is equivalent to
a drop in frequency.
A drop in the V BB value occurs if the element begins to consume current. If CMOS
technology is to be used, a drop occurs with each switch of the transistor, that is, in
each case of a change in its state. If a Trojan is installed in the circuit, adjacent ring
oscillators will register a more significant drop in V BB and frequency compared to
the parts of the microcircuit that do not contain Trojans.
In order to achieve the highest possible coverage, ring oscillators are installed over
the entire surface of the microcircuit. With the help of statistical methods used to
estimate frequencies of embedded ring oscillators, the probability of detection equal
to 100% is achieved. The efficiency of this approach in dealing with direct attacks
is considered fairly high, since the proposed manipulations have a direct impact on
the frequency of operation of ring oscillators, thereby revealing themselves when
performing corresponding functional tests.
This section presents a brief overview of the two methods of identification of
Trojans in microcircuits that were known at the moment of publication of this book.
However, the main problem currently is that none of these methods can guarantee
100% absence of a Trojan in the analyzed microcircuits.
Therefore, one of the most important tasks of developers of critical microcircuits is
development and unconditional compliance with the complexes of countermeasures
minimizing the possibility to introduce hardware Trojans into microcircuits during
any stage of its lifecycle, from design stages to organization of production and sales
through trusted supply channels.
5.1.18 Models of Multi-level Trojan Attacks
One of the types of a completely new class of cyberattacks—attack on cryptographic
algorithms—was first introduced by Ali et al. [3]. These so-called multi-level attacks
are based on the group interaction (synchronization of actions) of several individuals or even several professional teams of attackers involved in the development of
microcircuits and their production process.