Security and Privacy in Body Sensor Networks - E-Healthcare Systems and Wireless Communications - page 123

cated using a MAC but with no encryption support.
This default behavior can be overridden in code
using the setTransmitMode and setReceiveMode
commands in the TinySecMode interface. The
following is the syntax of these commands:

i.e. messages sent with the TINYSEC_
DISABLED transmission mode.
• TINYSEC_RECEIVE_ANY : this argument
values allows the receiver to accept any
message type from the sender.

commandresult_t setTransmitMode
(uint8_t mode);

The main disadvantage that, we believe, limits
the scalability of the TinySec security model and
its immunity against node capture attacks is the
key management mechanism that relies on a single
shared key for securing the communication among
a group of sensors. This key management model
jeopardizes the security of the whole network
if a single node is captured and its shared sym-
metric key is exposed. As discussed in the fourth
section on BSN key management, this static key
agreement hinders the scalability of the network
by requiring a complex key update mechanism to
refresh the static symmetric key and support the
addition and removal of wireless sensor nodes.

commandresult_t setReceiveMode
(uint8_t mode);

The argument to the setTransmitMode com-
mand determines the type of security mechanism
to be applied on the transmitted message. Three
possible argument values are supported:

• TINYSEC_AUTH_ONLY : this is similar
to the default TinySec operation where all
messages are only authenticated without
encryption.
• TINYSEC_ENCRYPT_AND_AUTH : this
argument value enables the confidentiality
and integrity services on the transmitted
messages by encrypting their contents and
authenticating them with a MAC.
• TINYSEC_DISABLED : this argument val-
ue results in the transmission of plain mes-
sages with no encryption or authentication
support.

TinyECC

TinyECC is a public key cryptography library
for TinyOS based on ECC. The main objective
behind TinyECC is to provide a public key cryp-
tosystem that can overcome the severe resource
limitations of wireless sensor nodes. Public-key
cryptography provides several security advantages
over symmetric- key cryptography in terms of
key management and digital signatures, however
these advantages come at the expense of high
computational and memory overhead. Designing a
public key cryptosystem that suits the limitations
of wireless sensors would definitely enhance the
security services in sensor applications.
ECC was the primary choice for supporting
public key operations in TinyECC. As discussed
in the second section, ECC is currently the most
efficient public key cryptosystem providing fast
computations and high security levels using small
key sizes. Using smaller key sizes than traditional
public key cryptosystems not only contributes
to faster processing but also to smaller digital

Similarly, the setRecieveMode interface takes
three possible argument values:

• TINYSEC_RECEIVE_AUTHENTICATED :
this argument value allows the receiver to
accept authenticated messages only, i.e.
messages sent with the TINYSEC_AUTH_
ONLY or TINYSEC_ENCRYPT_AND_
AUTH transmission modes.
• TINYSEC_RECEIVE_CRC : with this ar-
gument value, the receiver is only allowed
to receive plain messages with no security,