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\begin{document}
\title{Can't Touch This: Inertial HSMs Thwart Advanced Physical Attacks}
\subtitle{Changes of Major Revision compared to version submitted to TCHES 20/4}
\maketitle

This document lists the requested revisions we identified from the reviewers comments and explains how we adressed these
requests.

\paragraph{Lack of discussion of operational constraints}

As pointed out by Reviewer~B, our initial submission lacked a detailed discussion of the operational constraints of
Inertial Hardware Security Modules. We have adressed this with more than two pages of new content on the operation of
IHSMs in the new Sections~3.5 ``Long-Term Operation'' and~3.6 ``Transportation''.
% FIXME

\paragraph{Lack of discussion of improved cooling capabilities of IHSMs compared to traditional HSMs}

As Reviewer~D pointed out, our initial submission alluded to the possibility of facilitating cooling airflow through an
IHSM's security mesh and noted that this would allow for greater processing capabilities, but did not go into detail on
the extent of this effect. In our revised paper, we have extended Section~3.4 ``Mechanical Layout'' with an
order-of-magnitude estimation of this effect based on real-world benchmarks and information available from vendors of
traditional HSMs.

\paragraph{Mechanical Rotating Stage Attacks}

As pointed out by Reviewer~D, in our original submission our discussion of the Swivel Chair Attack discusses attacks by
by a rotating human attacker in depth and mentions the possibility of a fully mechanized attack robot. However, our
initial submission did not go into detail on the constraints of such a fully mechanized attack. In our revised paper we
have completed our discussion in this section with one half page of new content and one new diagram discussing
fully mechanized attack robots.

\paragraph{Comparison of IHSM attacks to those on traditional HSMs}

In addition to the previous point, Reviewer~D pointed out that the discussion of attacks on IHSMs in our initial
submission would have benefited from a more thorough contextualization of the attacks possible on traditional HSMs. In
response, we have significantly extended Section~4 ``Attacks'' with one page of new content in two new Subsections~4.2
``Attacks that don't work'' and~4.3 ``Attacks that work on any HSM'' that provide this missing context to guide the
reader.

\paragraph{Notes on future work}
Reviewer~D stated that they would find an outlook on the next design steps towards a practically usable design
interesting. We have adressed this at the end of Section~7 ``Conclusion'' to the extent of our current plans.

\paragraph{Design Artifact Availability}
Reviewer~D state that acceess to design artifacts would be useful for readers of the paper. While we cannot make our
design artifacts available as part of the peer review process as they contain a multitude of references to the
identities of the authors and their employer, we have added a brief appendix that in the publication version of our
paper will contain a link to the open-source repository containing all hardware, software and paper sources relating to
our research project.

\paragraph{Detailed discussion of contactless attacks}

Reviewer~C noted that like a traditional HSM an IHSM cannot prevent contactless attacks such as electromagnetic
sidechannel attacks or laser fault injection. While our initial submission acknowledged this property of our design, our
original submission did not provide a detailed discussion of its extent. In our revised paper, we have added a new
Section~4.2 ``Attacks that work on any HSM'' that provides more detail on contactless attacks. In this section we
observe that the IHSM design allows for some mitigations against contactless attacks due to the physically larger space
it can provide to its payload.

\paragraph{Justification of mesh monitor power consumption estimates}

A point noted by Reviewer~B is that in our initial submission we provided an estimate on the current consumption of an
IHSM monitoring cirucit without providing a detailed justification of our estimate. In response, we have extended
Section~5.3 ``Power transmission from Stator to rotor'' with a more detailed justification of this estimate.

\end{document}