Computer science encryption please do a-c please thank you refer to the chart

For the remaining questions, consider a 4-bit block cipher, described in hexadecimal by the following table: Plaintext Ciphertext Plaintext Ciphertext 4 You can think of this as a simple substitution cipher for hexadecimal digits. The table itself serves as the "key". 4. (4 pts) a. Encrypt the 4-block message feed using this cipher for each digit individually. b. Decrypt the ciphertext 5019 using this cipher. c. Why is it insecure to use a block cipher in this way