7^(3+j) mod 19 = A. 7^j mod 19 B. 1 mod 19 C. 7^3 + 7^j mod 19

7-3-j-mod-19-a-7-j-mod-19-b-1-mod-19-c-7-3-7-j-mod-19

7^(3+j) mod 19 =

A. 7^j mod 19

B. 1 mod 19

C. 7^3 + 7^j mod 19

D. All of the mentioned are true

I had been asked this question during a job interview.

This is a very interesting question from Number Theory topic in division More Number Theory of Cryptograph & Network Security

The correct choice is A. 7^j mod 19

To explain I would say: 7^(3+j)  mod 19 = 7^3 * 7^j mod 19 = 7^j mod 19 ( since 7^3 mod 19 = 1 ).