ABSTRACT
When examining Figure 1.1, it is interesting to note that until
1973, when James Ellis, Clifford Cocks, and Malcolm Williamson
first developed the concept of public-key encryption [121], and
1976, when Whitfield Diffie and Martin Hellman proposed their
revolutionary key distribution methodology [70], all cryptosystems
were symmetric-key based. Based on Figure 1.1, it is clear that
cryptographic algorithms used to ensure confidentiality fall within
one of two categories: symmetric-key (also known as secret-key
and private-key) and public-key. Symmetric-key algorithms use
the same key for both encryption and decryption. Conversely,
public-key algorithms use a public key for encryption and the
verification of Digital Signatures while using a private key for
tosystems tend to be hybrid systems that include both symmetric-
key and public-key algorithms. In a typical session, a public-
key algorithm will be used for the exchange of a session key and
to provide authenticity through Digital Signatures . The session
key is then used in conjunction with a symmetric-key algorithm.
