# Hack.lu 2013: Marvin is plain-Jane

Hey mister super-duper robo-dabster. We need you to tell us, what Marvin is!

What we know:

Marvin is
using brainpool p256r1.
His friend is called meneze or something. Or was it van-stone?

What we heard:

(23372093078317551665216159139784413411806753229249201681647388827754827452856 : 1)
71164450240897430648972143714791734771985061339722673162401654668605658194656
12951693517100633909800921421096074083332346613461419370069191654560064909824
What we need to know:

What Marvin is

The description made it very clear that the used crypto algorithm is Menezes-Vanstone. And if you are a bit into elliptic curve cryptography it’s obvious that if you know one part of the plain text (especially $x_1$) you are able to calculate the other one.

1. you know $y_1$ and $x_1$
2. therefore you know $c_1 = y_1 \cdot x_1^{-1}$
3. with $c_1$ you are able to calculate both possible values for $c_2$
4. with $c_2$ you know $x_2 = y_2 \cdot c_2^{-1}$
5. done

Due to the fact that “Marvin is” was highlighted that much in the description, we guessed that it was the first plaintext.