Protocols for Secure Communication in Wireless Sensor Networks

3.2. Attack Objectives 73
• Timeliness
• Origin
The first three of these points refer to the “classical” security properties that
have to be protected in virtually any security sensitive application. We consider
timeliness as an additional essential security goal in sensor networks. It may
be possible to subsume this goal under availability, but in many applications,
timing is crucial and seemingly insignificant delays could have severe impact.
When referring to the origin of some piece of data (or a message), we assume
that a party obtaining the data (for example, by reading from a sensor or
receiving a message) also obtains some statement about the association of the
data with its origin, i.e. the source from which it has been obtained. This statement
could be backed up by a digital signature, or it might be implicit as when
reading from a sensor. If the evidence supporting the statement is sufficiently
strong, the party may decide to attests its finding, thus further supporting the
statement. It is therefore crucial that a statement about the origin of a piece of
data cannot be forged or tampered with by an attacker.
Usually, the origin of a message refers to the entity that has generated the
message. Origin authentication is based on some feature of the source, such as
a public/private key pair, a common secret key, location, or a biometric attribute
(in real life, voice is often used).
Integrity and origin authentication are often achieved through the same mechanisms.
An important mechanism is the concept of message authentication
code (MAC). Such a MAC provides a means for the receiver of a message to
verify the message’s origin and its integrity at the same time. Both concepts are
closely connected, as when the integrity of a message is violated, it is essentially
transformed into a different message, which has a different origin as well.
Vice versa, if the origin of a message cannot be verified, it does not necessarily
follow that the integrity of the message has been violated. Stated differently,
even if we don’t know where a message comes from, it could still be a valid
message. Thus, it is valid to say that origin authentication implies integrity, but
not the other way around.
3.2.2 Resource Types
It very much depends on the level of abstraction what components of a networked
computer system are regarded as valuable resources that require protection.
In a transaction-oriented system, the database would be the most valuable
resource. On a home desktop PC, personal information such as credit card