A User Centric Security Model for Tamper-Resistant Devices

8.4 Analysis of the Runtime Protection Mechanism
8.4.1.1 Operand Stack Integrity
Barbu et al. [217] proposed an attack in which values stored on the operand stacks were
manipulated by fault injections. They also proposed a countermeasure to this attack that
was based on calculating the integrity measurement of the whole of the operand stack,
every time the state of the stack was required to be veried. We rened their approach
and removed the need to perform integrity measurement of the entire operand stack on
each validation. In addition, we made the validation process continuous thus checking
the integrity of the operand stack on each pop and push operation. If a malicious user
changes values on the operand stack, the runtime security manager can not only detect the
modication but can also provide error correction service by providing the correct value
that was stored on the operand stand. This is possible because the integrity stack stores
values pushed on to the operand stack as individual components of the integrity chain (i.e.
V Ins-n =S r ⊕Σ n i=1 V i). Furthermore, our proposal also protects against parallel fault injection
attacks that could target both operand and integrity stack simultaneously. The reasoning
behind this is based on the use of S r (random number) that makes the values stored on
the integrity stack unpredictable over dierent execution sessions of the same application.
Thus making it dicult for an adversary to know the values stored on the integrity stack,
even if he has the knowledge of all values on the operand stack.
8.4.1.2 Control Flow Analysis
The control ow analysis performed by the runtime security manager during the execution
of an application eectively prevents control ow attacks. If an attacker has the capability
of multiple fault injections simultaneously, (which is beyond the stated capability of our attacker
in section 8.3.2) then he can in theory aect the runtime security manager execution.
Nevertheless, even with simultaneous injection the attacker may be able to skip a node in
the execution tree but the runtime security manager calculation on the subsequent nodes
will reveal an illegal path of execution. Therefore, even in the parallel injection model the
runtime security manager will detect the erroneous execution path, unless the attacker will
constantly keep on introducing injections for the whole execution of an application.
8.4.1.3 Bytecode Integrity
This countermeasure is proposed to prevent an adversary to change an application while
it is stored on a non-volatile memory (capability four of an adversary discussed in section
8.3.2). To avoid such modications, the runtime security manager generates a hash
of individual methods that are requested by the JCVM. If the hash matches the value
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