1. We need to encrypt the plaintext message csula. (1) Use additive cipher with key =20 to obtain the ciphertext. (2) Use Vigenre Square by starting from the third substitution row (i.e., labeled C row) to obtain the ciphertext. (3) Use the ASCII table as below (For example, t = 74 in Hex or 1110100 in binary.) to find the binary number of the plaintext, then use transposition key pattern: 1->4, 2->7, 3->1, 4->5, 5- >6, 6->2, 7->3 to obtain the ciphertext. Note: the block size is 7. (4) Use a secret key V to encrypt each letter of the plaintext via XOR to find the ciphertext.