ABSTRACT
Modern cryptography is one of the building blocks in the design of wireless sensor networks (WSN). The two fundamental categories are symmetric key schemes and asymmetric key schemes. In symmetric key schemes, the communicating pair has to agree on secret and authentic keying material before initiating encrypted communication. Hence, a major drawback with such schemes is the requirement of an authenticated and confidential channel for distributing keying material. The need for a constant trusted third party weakens the applicability of symmetric key cryptography in distributed networks. Furthermore, problems with key management (Chapter 6) and nonrepudiation services in symmetric key schemes exacerbate its usage in an ad-hoc network such as WSN. In 1975, Whitfield Diffie and Martin Hellman introduced public-key crypto graphic schemes that required only an authentic key exchange between the communicating parties (Diffie and Hellman 1976). This was the first discrete log system. In this scheme, each communicating entity had a private and a corresponding public-key pair such that retrieving the private key from the corresponding public key was computationally infeasible. This revolutionary approach laid the foundation for modern cryptography. In 1977, the first fully conceptualized public-key cryptographic
algorithm was proposed by Ron Rivest, Adi Shamir, and Leonard Adleman (RSA algorithm; Rivest et al. 1978). The security of such public-key cryptographic schemes depended on the integer factorization problem or the discrete log problem. In 1984, ElGamal proposed public-key based signature and encryption schemes based on the discrete log problem (ElGamal 1984).
