# Using Montgomery ladder to calculate the coordinates

In one of my assignments I need to solve the problem below:

For a Montgomery curve $3v^2 = u^3+u^2+u$ over ${\mathbb{F}}_{11}$ and point $P = (9,8)$, compute the $x$ coordinate of $3P$ using the Montgomery ladder.

I just need a hint to get an idea and not the whole answer. if anyone with some useful links would also be appreciable. As I tried to search google for this but was not able to get any idea.

Is it that I need to find it as $3P = 2P + P$ because I found one question about scalar multiplication here. but then I think it is not the correct way to use the Montgomery ladder.

• Do you know what the Montgomery ladder algorithm is? – poncho Jan 16 '16 at 1:57
• Yes I have read about it and I know that we double when we have bit 1 and we add if bit 0. But I am not able to apply here. Or otherwise I haven't that much knowledge about it. – TechJ Jan 16 '16 at 1:59
• – poncho Jan 16 '16 at 4:58