iTP Secure WebServer System Administrator's Guide (Version 7.0)

Security Concepts
iTP Secure WebServer System Administrator’s Guide—523346-012
D-4
Public Key Systems
key) never leaves the possession of its owner. Neither key is of any value without the
other.
Public key cryptography can be used for both privacy (encryption) and authentication
(digital signatures).
Encryption
For encryption, public key systems work as follows: To send a private message to
Juliet, Romeo looks up Juliet's public key in a public directory. Using this public key, he
encrypts his message and then sends it to Juliet across a normal (nonsecure)
communications channel. Upon receiving Romeo’s message, Juliet uses her private
key, which is uniquely associated with her public key, to decrypt it.
Because only Juliet has access to her private key, no one else can decrypt Romeo’s
message. Therefore, even if Capulet, Juliet’s father, intercepts Romeo’s message, he
cannot read it – unless he gains access to Juliet’s private key.
Session Keys
In practice, encrypting data with a public key system is computationally slow and
therefore expensive. Secret key systems, based on a technology such as the Data
Encryption Standard (DES), are much faster.
Figure D-2. Public-Key Systems
Romeo Juliet
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