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communication. The main focus will be on the
secure communication among the sensor nodes
in the BSN network. Data security between the
BSN controller and the base station and between
the base station and the enterprise servers is well
researched in the literature and can be provided
using time-tested security protocols such as SSL
and TLS (Rescorla, 2001). The SSL/TSL proto-
col suites support authenticated key agreement
mechanisms, typically, using the Diffie-Hellman
protocol and provide data confidentiality and in-
tegrity security services. As stated in the previous
section, these protocols rely on resource-intensive
public-key operations in the key management
phase which renders them extremely heavy for
applications on limited sensor nodes.
The data confidentiality and integrity services
among the BSN sensor nodes can be provided by
extending the biometric key agreement presented
in the previous with encryption and Message Au-
thentication Code (MAC) security mechanisms.
A typical protocol employing these cryptographic
constructs is presented as follows:
Assume that the master and slave sensor nodes
have already established a session key using the
biometric key agreement mechanism. The ses-
sion key
K
s
generated at the master sensor may
not be equal to the session key
K''
s
retrieved at
the slave sensor. This is due to the fact that the
error correction decoding function may not be
able to correct the bit errors resulting from the
inaccuracy in biometric measurements. If the
master sensor has a message
M
to send to the
slave sensor, it starts by encrypting
M
using
K
s
to
get the ciphertext
C
. This encryption step ensures
the confidentiality of
M
when transferred over the
wireless link. Afterwards, the master sensor applies
a MAC operation on
C
using
K
s
to get the MAC
μ
. The MAC operation supports the integrity of
the network message. Finally, the master sensor
sends
C
and
μ
to the slave sensor over the wireless
communication channel.
Upon receiving
C
and
μ
, the slave sensor ap-
plies a MAC operation on
C
using
K''
s
to get the
MAC
μ'
. If the calculated MAC
μ'
equals the
received MAC
μ
the receiver assumes that the
network data is not tampered with over the wire-
less channel and that the derived session key
K''
s
equals the generated session key
K
s
generated by
the sender. In this case, the encrypted ciphertext
C
is accepted and
M
is retrieved by decrypting
C
using
K''
s
.
Note that if
μ'≠ μ
, this implies that either the
data is corrupted or the error correction decoding
was unsuccessful in retrieving the correct ses-
sion key. In both cases, the encrypted message is
considered invalid and is dropped by the slave.
A schematic diagram presenting a formal
description of biometric key agreement followed
by the confidentiality and integrity protocol steps
is provided in Figure 6.
BSN PRIVACY-PRESERVING
PROTOCOLS
BSNs collect vital physiological signals from the
human body and transmit it to be stored in external
storage sites that may not be fully trusted. The
collected information contains sensitive medical
data whose privacy should be preserved during
the whole information lifecycle. In the previous
two sections we described how to protect the se-
curity of data when transmitted over the network
links. In this section we continue by presenting
some security mechanisms for preserving the
privacy of data when stored on external, possi-
bly non-trusted, storage sites. The main privacy
requirements that we focus on in the discussion
are presented as follows:
1. Protecting the privacy of data by preventing
the storage site from inspecting or analyzing
its content. The site is assumed to be trusted
for preserving the integrity of data storage.
2. Specifying well-defined access control
mechanisms that identify the entities au-
thorized to access the data and the exact
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