2

I am trying to implement a PoC of some variant of monero. Currently for start, I want to generate the expression G*a*i^2 given all the scalars (a,i,2).

I've lost my way while looking at Monero libraries since the structs and the names of the functions and their inputs/outputs are not clear and well documented.

3

Assuming G is the base point and i is a scalar (the convention is to write points in capital letters and scalars in lowercase letters):

rct::key tmp; sc_mul(i.bytes, i.bytes, i.bytes); // i = i^2 sc_mul(tmp.bytes, a.bytes, i.bytes); // tmp = a * i^2 rct::scalarmultBase(tmp, tmp); // tmp = a * i^2 * G

The rct API is easier to use than the fe/ge API, but it has a single type for points and scalars, which make it more error prone. sc_mul (scalar multiplication) is the fe API, and scalarmultBase is the rct API.

  • Btw fe (field elements) and scalars are slightly different things. Field elements are in the range of the size of the prime finite field which is of size q (2^255-19), and scalars are in the range of the prime group size of the base point G (2^252+....). – knaccc Aug 6 '18 at 14:24
  • Ok, got it. One more related question, lets say I want an exponent bigger than 2 (for i), say i^30 ; is there an efficient way to do it? (the naive way of doing it in an iterative manner seems really inefficient). – Shak Aug 7 '18 at 6:46
  • 1
    en.wikipedia.org/wiki/… – user36303 Aug 7 '18 at 13:30
  • I assume that i is of type key, while also temp. Though, temp is a point on the curve and i is a scalar. How is it possible? – Shak Aug 7 '18 at 13:35
  • Yes. As I said in the anwer, "a single type for points and scalars". You don't have to use it for the fe/ge API though, there are other types such as ge_p3 for points. – user36303 Aug 7 '18 at 19:37

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.