Computer and Information Security Handbook, 3rd Edition

4. Modern Symmetric Ciphers

Computers internally represent printable data in binary format as strings of zeros and ones. Therefore any data are represented as a large block of zeros and ones. The processing speed of a computer is used to encrypt the block of zeros and ones. Securing all data in one go would not be practical, nor would it secure the data; hence the scheme was to treat data in chunks of blocks, which led to the concept of block ciphers.

Table e46.2

Monoalphabetic Substitution Cipher

X	0	1	2	3	4	5	6	7
y	3	0	5	2	7	4	1	6

Table e46.3

Transposition Cipher

1	2	3	4	5
3	1	4	5	2

The most common value of a block is 64, 128, 256, or 512 bits. You will observe that these values ...