Page 117 - CISSO_Prep_ Guide

people that want to communicate must have a separate key that
only they use. This requires the storage and distribution of many
keys.

Key distribution is also a challenge since there must be a secure
way to share the symmetric key between the two parties without
anyone else getting a copy. This means that the key cannot be
sent in the same channel as the data but must rather be sent out
of band or in some other distribution channel (courier, fax,
phone).

Asymmetric Algorithms

Asymmetric Algorithms are a relatively recent development. In
the 1970s, Diffie-Hellman developed a method of encryption
based on two different keys. The two keys are mathematically
related. One key is known as the private key; the other is known
as the public key. It is not computationally feasible to learn the
value of the private key even though a person knows the value
of the public key. Therefore a person may freely and openly
give their public to everyone without risking the compromise of
their private key. Because asymmetric algorithms use a public
and private key pair, they are commonly referred to as public-
key algorithms.

The main use of most asymmetric algorithms is to support the
implementation of symmetric key algorithms and for digital
signatures, which will be examined later.

Diffie-Hellman was used to allow two parties that wanted to
communicate over an untrusted network to establish a secret key
that could be used for symmetric (fast) encryption. Therefore it