674
7 Countermeasures Against Hardware Trojans
consists in implementation of the special authentication mechanism in order to
prevent leakage of any critical information caused by unauthorized access to the
scan channel. In particular, scan structure in [68] masks the scanning output with
pseudo-random numbers, and the users are unable to embed their correct verification
in their test vectors; in [54], the scan structure masks scanning elements if the attempt
to switch to safe testing mode has failed. Scanning protection based on low hardware
costs of auhtentication was suggested in [69], where scan output is switched until
authentication is passed. Unlike previous approaches, [67] suggest the method of
isolating important data registers (e.g., the ones containing keys) when the circuit is
used in a non-safe mode. In IIPS [32], the authors use the Vim-Scan suggested in
[69] but with small changes aimed at improving effective security protection. This is
done mostly on the basis of the fact that [67] requires no structural changes in scan
chains besides trivial interface setting and thus minimizes structural modifications
in SoC functional cores to simplify the process. The method suggested in [69] is
also distinguished by good scalability as compared to other approaches; it can be
successfully used for microcircuits with various integration levels.
7.3.6 Additional Capabilities of the IIPS Unit
The IIPS test protocol described [32] was based on implementation of the test infrastructure of the IEEE 1500 standard. It should be noted that IIPS security provision
functions are universal in terms of consistency with various improved configurations of the IEEE 1500 architecture. In practice, IIPS effectiveness can be improved
significantly if qualified developers properly use all additional possibilities of IEEE
1500.
Test protocols are used to identify ScanPUF and hardware Trojans can be easily
adapted for the use of parallel interface to transmit test vectors on condition of using
the TAM parallel architecture, which can significantly reduce the total analysis time.
Clearly, in case with a minimally configured IEEE 1500 infrastructure, this approach
to detecting hardware Trojans on system buses can be implemented only on condition
of presence of the LOS unit, since standard wrapper elements of core outputs usually
do not support the capture operation in the EXTEST mode. However, if the wrapper
is implemented using WBCs with enhanced scan functions, or the infrastructure is
extended to support delay-fault test [70], a broadside capture can be realized at the
system bus inputs for a standard LOC test scheme. In this case, a significant increase
in the possibilities of detection of hardware Trojans can be expected.
The IIPS methodology also demonstrates good possibilities of functional scaling
for integration of even greater functions to ensure security or test infrastructures with
minimum additional hardware costs. IIPS can also be used to provide protection from
other attack models, including attacks on cryptographic systems via side channels.
For example, IIPS can be equipped with a noise injector [71] to mask dynamic
current, which in turn masks the possibility of organizing key-related information
leak through transient current.
7 Countermeasures Against Hardware Trojans
consists in implementation of the special authentication mechanism in order to
prevent leakage of any critical information caused by unauthorized access to the
scan channel. In particular, scan structure in [68] masks the scanning output with
pseudo-random numbers, and the users are unable to embed their correct verification
in their test vectors; in [54], the scan structure masks scanning elements if the attempt
to switch to safe testing mode has failed. Scanning protection based on low hardware
costs of auhtentication was suggested in [69], where scan output is switched until
authentication is passed. Unlike previous approaches, [67] suggest the method of
isolating important data registers (e.g., the ones containing keys) when the circuit is
used in a non-safe mode. In IIPS [32], the authors use the Vim-Scan suggested in
[69] but with small changes aimed at improving effective security protection. This is
done mostly on the basis of the fact that [67] requires no structural changes in scan
chains besides trivial interface setting and thus minimizes structural modifications
in SoC functional cores to simplify the process. The method suggested in [69] is
also distinguished by good scalability as compared to other approaches; it can be
successfully used for microcircuits with various integration levels.
7.3.6 Additional Capabilities of the IIPS Unit
The IIPS test protocol described [32] was based on implementation of the test infrastructure of the IEEE 1500 standard. It should be noted that IIPS security provision
functions are universal in terms of consistency with various improved configurations of the IEEE 1500 architecture. In practice, IIPS effectiveness can be improved
significantly if qualified developers properly use all additional possibilities of IEEE
1500.
Test protocols are used to identify ScanPUF and hardware Trojans can be easily
adapted for the use of parallel interface to transmit test vectors on condition of using
the TAM parallel architecture, which can significantly reduce the total analysis time.
Clearly, in case with a minimally configured IEEE 1500 infrastructure, this approach
to detecting hardware Trojans on system buses can be implemented only on condition
of presence of the LOS unit, since standard wrapper elements of core outputs usually
do not support the capture operation in the EXTEST mode. However, if the wrapper
is implemented using WBCs with enhanced scan functions, or the infrastructure is
extended to support delay-fault test [70], a broadside capture can be realized at the
system bus inputs for a standard LOC test scheme. In this case, a significant increase
in the possibilities of detection of hardware Trojans can be expected.
The IIPS methodology also demonstrates good possibilities of functional scaling
for integration of even greater functions to ensure security or test infrastructures with
minimum additional hardware costs. IIPS can also be used to provide protection from
other attack models, including attacks on cryptographic systems via side channels.
For example, IIPS can be equipped with a noise injector [71] to mask dynamic
current, which in turn masks the possibility of organizing key-related information
leak through transient current.