Question

In the elliptic curve group defined by y2= x3- 17x + 16 over real numbers, what is 2P if P = (4, 3.464)?

(a) (12.022, -39.362)

(b) (32.022, 42.249)

(c) (11.694, -43.723)

(d) (43.022, 39.362)

The question was asked in an online quiz.

My question is from Elliptic Curve Arithmetic/Cryptography topic in division Other Public Key Cryptosystems and Cryptographic Hash Functions of Cryptograph & Network Security

Answer 1

The correct answer is (a) (12.022, -39.362)

The explanation is: From the Doubling formulae:

λ = (3*(4)2+ (-17)) / 2*(3.464) = 31 / 6.928 = 4.475

x3=  (4.475)2- 2(4) = 20.022 – 8 = 12.022  and

y3= -3.464 + 4.475(4 – 12.022) = – 3.464 – 35.898 = -39.362

Thus 2P = (12.022, -39.362).