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TABLE 6.2: Comparison of popular symmetric trust establishment schemes
in WSNs.
Scheme
Energy
awareness
Memory
consumption
Network
resilience
Network
connectivity
Additional
requirement
Eschenauer
[Es-
Average
High
Poor
Average
None
chenauer
and
Gligor, 2002]
Jolly [Jolly et al.,
2003]
Very good
Very low
Poor
N/A
None
Chan [Chan et al.,
2005b]
Good
High
Good
Average
Attack proba-
bilities
Du
[Du
et
al.,
Good
Low
Average
Good
Location
information
2004]
Liu
[Liu
et
al.,
Average
High
Good
Average
None
2005a]
Eltoweissy
[El-
Average
Low
Good
Average
None
toweissy
et
al.,
2006]
plementation of asymmetric cryptographic protocols in resource-constrained
sensor devices becomes possible. In this section, we review several public key
cryptosystems for trust establishment systems in WSNs.
Watro et al. [Watro et al., 2004] proposed a set of public key-based pro-
tocols, called TinyPK, to support authentication and key agreement between
a sensor network and a commonly trusted third party outside the sensor net-
work. They exploited the e ciency of the public operations in RSA [Rivest
et al., 1978] cryptosystems with the characteristic that the public operations
are very fast compared to other public key technology computations by explic-
itly choosing some small indices as public keys. Their protocols are specially
designed such that the computationally expensive operations are placed on the
third parties whenever possible. However, some basic functions, such as revo-
cation of compromised private keys, are not supported. Using their protocols,
they demonstrated that the RSA [Rivest et al., 1978] and Di e-Hellman key
agreement techniques [Di e and Hellman, 1976] can be deployed in existing
sensor network devices.
As for energy e cient cryptosystems, there are some other options pro-
posed, such as the XTR public key system [Lenstra and Verheul, 2000], and El-
liptic Curve Cryptography (ECC) [Koblitz, 1987, Miller, 1985]. Among them,
ECC receives most attention. ECC operates on groups of points over elliptic
curves. Its security stems from the hardness of elliptic curve discrete loga-
rithm problem (ECDLP). To solve the integer factorization problem of RSA,
there are sub-exponential algorithms. However, only exponential algorithms
are known for solving the ECDLP. This is the reason why ECC can achieve
the same level of security with smaller key sizes. In the future, it is believed
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