IEEE Consumer Electronics Magazine - January/February 2022 - 9

technology and its potential to capture the necessary
information to unlock a vault. This fear is
reinforced with the use of electric potential
probes that enable remote capturing of ECG and
PPG.13;14
Due to this development in adversary capabilities,
it is necessary to explore new ways of
protecting the fuzzy vault construction and the
schemes that rely upon it while minimizing the
incurred overhead. We, therefore, propose an
original scheme named RAFV (rotation assisted
fuzzy vault) that builds upon the fuzzy vault
scheme by leveraging channel side characteristics
known as RSSI (received signal strength
indicator) to obfuscate the locked vault. If an
adversary is capable of collecting physiological
signals originating from the target BAN sensors
then they would be able to carry out impersonation
attacks if the current iterations of PSKA,
OPFKA, and schemes similar in nature are used.
This is because adversaries can utilize a remotely
captured signal to unlock the vault and
obtain the key concealed within it, compromising
all future communication between the nodes
targeted. However, RAFV will ensure that knowledge
of the physiological signal alone does not
provide access to the secret concealed within
the vault. This is because any attempt to acquire
the secret requires knowledge of how the vault
has been obfuscated, which is not impacted by
the leakage of locking elements to an adversary.
OUR PROPOSAL
In this section, we will present the main idea
of our original scheme named RAFV, describe its
locking and unlocking process and discuss its
robustness against brute force attacks that may
target the constructed vault.
RAFV: An Overview
The objective of RAFV is to secure any
authentication scheme that uses the fuzzy vault
construction mechanism, wherein the elements
used for locking and unlocking the vault are susceptible
to leakage within a wireless network.
RAFV can be seen as an extension to the fuzzy
vault scheme and is situated within the postlocking
and pre-unlocking phase of this scheme
(see shaded areas in Figure 1). RAFV shall
January/February 2022
transmit an obfuscated fuzzy vault from the
sender to the receiver, any attempt by an adversary
to unlock the intercepted vault would fail
even if the adversary is aware of the full set of
locking elements. This is because RAFV does not
conceal the polynomial but rather " corrupts " it
preventing successful unlocks until the vault has
been " repaired. " The vault shall be obfuscated
by dividing it into quadrants and rotating the
points within each quadrant around its center.
RAFV relies on the ability to agree upon a
sequence of bits in an out-of-band manner to
ensure that an adversary cannot obtain this
sequence. This sequence can be seen as a symmetric
key that is used to lock and unlock the
vault itself. To achieve this, RAFV makes use of
RSSI which is a measurement of the power contained
in the received signal. This measurement is
only computed locally on the device and cannot
be obtained by an adversary, which makes it ideal
for attempting to harden the security of the fuzzy
vault scheme. RSSI reconciliation is a process that
enables the two BAN nodes to agree upon the key
that shall be used to secure the vault. RSSI values
between two wireless devices are prone to discrepancies
and need to be corrected, therefore we
model the errors as communication errors and
use error correction codes, such as Reed-Solomon
(RS), to ensure that the sender and the receiver
are in agreement (i.e., they measure the same
value). This process has been used in many key
generation and key agreement schemes, including
the ones applied in BAN such as by Li et al.15-17
Locking and Unlocking Process in RAFV
RAFV locking phase consists of the following
steps. 1) Measuring the RSSI value between the
two BAN devices. 2) The sender generates RS
coefficients and sends them to the receiver.
3) The receiver uses the received RS coefficients
to correct its " copy " of RSSI, if the receiver fails
to correct the errors the process should be
restarted from the first step. 4) The sender constructs
the locked fuzzy vault. 5) Dividing the
vault into several quadrants. 6) Assigning a rotation
direction and order for each quadrant.
7) Executing the rotation. These steps are summarized
in Figure 2.
As for the unlocking phase, upon reception of
the fuzzy vault from the sender BAN device the
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