Why is it not practical to use an arbitrary reversible substitution cipher of the kind

shown in Table 3.1?

Transcribed Image Text:

Table 3.1 Encryption and Decryption Tables for Substitution Cipher of Figure 3.2 Plaintext 0000 0001 0010 0011 0100 0101 0110 0111 1000 1001 1010 1011 1100 1101 1110 1111 Ciphertext 1110 0100 1101 0001 0010 1111 1011 1000 0011 1010 0110 1100 0101 1001 0000 0111 Ciphertext 0000 0001 0010 0011 0100 0101 0110 0111 1000 1001 1010 1011 1100 1101 1110 1111 Plaintext 1110 0011 0100 1000 0001 1100 1010 1111 0111 1101 1001 0110 1011 0010 0000 0101