Hardware Reference
In-Depth Information
Understanding the disadvantages of hardware
crypto devices
Adding hardware cryptographic devices doesn't automatically make your project
secure
. In
the following sections, we'll discuss some of the downsides to using cryptographic hard-
ware and some of the concerns you would need to resolve when using them in your project.
Lacking cryptographic flexibility
A hardware cryptographic device is generally not configurable. This is usually by design
but the implication is that it is difficult, if not impossible, to alter the cryptographic behavi-
or of the device. If you select a chip that performs encryption with a limited key size, you
will not be able to upgrade the device with a stronger key size later. It is generally easier to
update software-based encryption systems.
Exposing hardware-specific attack vectors
While an isolated crypto processor may reduce attacks or exploits from the software, it of-
ten allows more sophisticated hardware-based attacks. There are three categories of
hardware-based attacks: noninvasive, invasive, and semi-invasive (Skoroboga, 2011). Non-
invasive attacks treat the chip as a black box and attempt to manipulate the surrounding en-
vironment to perform an exploit. Successful non-invasive attacks include performing a
Dif-
ferential Power Analysis
(
DPA
) to monitor the chip as it performs an encryption al-
gorithm. By measuring the power usage during the encryption operation, it is possible to
see the key through distinct power signatures. An invasive attack usually involves physic-
ally destroying the chip in some manner to gain access to its internals. Semi-invasive at-
tacks may involve some sort of laser imaging to observe or interfere with the chip.
Note
To perform a glitch attack, an attack attempts to manipulate the executing instruction by in-
jecting a fault (Bar-El, 2004). Colin O'Flynn, a security researcher, has a concise and clear
example of how a glitch attack can cause a password-checking microprocessor to fail:
ht-
Obfuscating implementation details
A final consideration is that while chip vendors may publish the interface to their device,
the internals are often proprietary. This is similar to a software vendor who publishes the
