Question

Multiply the point P=(8, 1) by a constant 3, thus find 3P, in the elliptic curve E13(1, 1)

(a) (10,7)

(b) (12,6)

(c) (11,1)

(d) (9,8)

I had been asked this question in final exam.

The origin of the question is Elliptic Curve Arithmetic/Cryptography topic in section Other Public Key Cryptosystems and Cryptographic Hash Functions of Cryptograph & Network Security

Answer 1

The correct answer is (a) (10,7)

To elaborate: P+P=2P       then, 3P=2P+P

Thus we get Q=3P = (10, 7).