(a) Using the extended Euclidean algorithm, find the multiplicative inverse of 504 mod 67.
(b) Decrypt the following ciphertext, which has been encrypted using Caesar cipher:
YMNXJ CFRNS FYNTS UFUJW NXVZN YJJFX D
(c) (i) Construct the Playfair matrix (5x5) using the keyword: cryptology
(ii) Encrypt the following plain text using the above matrix: billa bong