$2.$ Protocol errors may occur with careless use of the RSA crypto$-$system. Here is an example: Each character is expressed with a number, A$0,$ B$1,...,$ Z$25,$ and then each of these numbers is encrypted with RSA on its own and sent to the recipient.

a$)$ How can a third party with access to these messages easily decrypt these messages without knowing the RSA key? Explain.

b$)$ N $=18721,$ e$=25$ and encrypted message $6400,1375,1759,1759,17173,17173$

If so$,$ find the clear message.

Hint: $(5^5)^5=1759,14^25=1375,2^50=17173$ in mod $18721$