Fundamentals of Information Encryption - Multilevel Security for Relational Databases - page 69

for key transfer. In conventional encryption, as shown in Figure 4.2,
the sender encrypts the data (plaintext) using the encryption key and
the receiver decrypts the encrypted data (ciphertext) into the origi-
nal data (plaintext) using the decryption key. In symmetric encryp-
tion, encryption and decryption keys are identical. Figure 4.3 shows
the public key encryption (asymmetric encryption) in which the
encryption and decryption keys are different. Public key cryptogra-
phy solves the problem of conventional cryptosystems by distributing
the key [45,46]. Table 4.1 shows a comparison between symmetric
encryption and asymmetric encryption.
There are two types of cryptosystems:

• Symmetric (private) key cryptosystems
• Asymmetric (public) key cryptosystems

Sender Transmission Receiver

X e K d

Message
Source

Message
destination

Cryptanalyst
(Attacks)

X X

Encryption
Algorithm

Decryption
Algorithm

Y Y

K

K

Secret
Key

Secure
Channel

Figure 4.2 Model of symmetric encryption.

X

Cryptanalyst

e source A e destination B

Message
source

X Y X

Encrypt Decrypt Destination

K d

K e

Key pair
source

Figure 4.3 Asymmetric-key encryption.