Suppose Michael creates an RSA cryptosystem with a very larg

Suppose Michael creates an RSA cryptosystem with a very large mod­ulus n for which the factorization of n cannot be found in a reasonable amount of time. Suppose that Nikita sends messages to Michael by representing each alphabetic character as an integer between 0 and 26 (A corresponds to 1, B to 2, etc., and a space to 0), then encrypts each number separately using Michael\'s RSA cryptosystem. Is this method secure? Explain your answer.

Solution

This method is not secure, it is just equal to a \"Ceaser Cipher\", that is a permutation of letters of alphabet, which is well-known to be easily broken using a frequency analysis.