4. (10 points) The following ciphertext PULCL YTHRL LEJLW APVUZ HULEJ LWAPV UKPZW YVCLZ AOLYBSL was obtained using a Vigenre cipher with a keyword of length p. Here is the frequency table for the letters in this ciphertext rA | B | C | D | E | F | G | H | | | J | K | L | M | N | O 3 120 2 0 0 2 0 210 0 01 PC2 | R | S | T | U | V | W | X | Y | Z 4 0 1 11 4 3 3 0 3 3 (a) Compute the index of coincidence and use it to estimate the length of the keyword. (b) Decrypt the ciphertext. 4. (10 points) The following ciphertext PULCL YTHRL LEJLW APVUZ HULEJ LWAPV UKPZW YVCLZ AOLYBSL was obtained using a Vigenre cipher with a keyword of length p. Here is the frequency table for the letters in this ciphertext rA | B | C | D | E | F | G | H | | | J | K | L | M | N | O 3 120 2 0 0 2 0 210 0 01 PC2 | R | S | T | U | V | W | X | Y | Z 4 0 1 11 4 3 3 0 3 3 (a) Compute the index of coincidence and use it to estimate the length of the keyword. (b) Decrypt the ciphertext