DATABASE SECURITY - Database Design and Development: An Essential Guide for IT Professionals - page 508

Plaintext

Encryption key

Encryption
algorithm

SENDER

Ciphertext

RECEIVER

Ciphertext

Decryption key

Decryption
algorithm

Plaintext

Figure 16-9 Elements of encryption.

• A decryption key to decode ciphertext
• A decryption algorithm to change ciphertext back into original plaintext

Figure 16-9 shows the elements of encryption. Note the use of the keys and where
encryption and decryption take place.
The underlying idea in encryption dictates the application of an encryption algo-
rithm to plaintext where the encryption algorithm may be accessible to the intruder.
The idea includes an encryption key specified by the DBA that has to be kept secret.
Also is included a decryption algorithm to do the reverse process of transforming
ciphertext back into plaintext.
A good encryption technique, therefore, must have the following features:

• Fairly simple for providers of data to encrypt
• Easy for authorized users to decrypt
• Does not depend on the secrecy of the encryption algorithm
• Relies on keeping the encryption key a secret from an intruder
• Extremely difficult for an intruder to deduce the encryption key

Just to get a feel for an encryption scheme, let us consider a simple example
before proceeding further into more details about encryption. First, we will use a
simple substitution method. Second, we will use a simple encryption key. Let us say
that the plaintext we want to encrypt is the following plaintext:

ADMINISTRATOR

Simple Substitution Use simple substitution by shifting each letter in the plain-
text to three spaces to the right in the alphabetic sequence. A becomes D, D
becomes G; and so on. The resulting ciphertext is as follows: