Encryption question

For the remaining questions, consider a 4-bit block cipher, described in hexadecimal by the following table: Plaintext Ciphertext|Plaintext Ciphertext 0 8 a e 1 C 9 d 2 f 0 3 6 b 7 4 3 5 5 8 d b 6 4 9 7 2 f You can think of this as a simple substitution cipher for hexadecimal digits. There is no key" other than the table itself. 4. (4 pts) a. Encrypt the 4-block message cafe using this cipher for each digit individually. b. Decrypt the ciphertext b99b using this cipher. c. Why is it insecure to use a block cipher in this way? Do not critique the block cipher itself, but only how it is used