Nils (or anyone else),
    I know this was a while ago but I just got back to it. The one thing that
I don't understand about the calls to  EC_POINT_mul() and EC_POINTs_MUL() are
what is n & m? Are they some aspect of the curve being used?  Ar they the
affine coordinates of the other point?  all I know about them is that they are
BIGNUM's.
    I need to do 2 things, multiply 2 points together and add two points
together.

Thanks,

Frank

Nils Larsch wrote:

> Hi Frank,
>
> Frank wrote:
> > Nils,
> >     Thanks for the information. Had a couple more questions below.
> ...
> > > The result is stored in 'r' or EC_POINT_mul(group, r, n, p, m, NULL)
> > > calculates r = n * g + m * p , where n,m are integers, g is the
> > > generator of the group and p is another point on the elliptic curve.
> >
> > g or generator is the well known base point right?
>
> g is the generator of the cyclic group which we use for our ec operation
> => yes, it's the base point of our group
>
> > n,m are integers, hmmm ok, can you elaborate a little? If I'm trying to
> > multiply two points i.e. p * ??
>
> We have a elliptic curve G , a point on that curve g and we define an
> operation '+' via the usual 'chord-tangent process' (normally called
> addition) giving us a well defined group. n*p (where n is an integer
> and p is a point on the curve) is defined in the obvious way:
> n*p = /sum_{i=0}^n p. I guess you really want to have p + q
> (p,q points on the curve) and not p*q.
>
> >  is n, m properties of that other point?
> > i.e. the x,y affine coordinates of that point?
>
> no, n and m are arbitrary integers
>
> > > EC_POINT_mul() is only another interface for EC_POINTs_mul() (see
> > > crypto/ec/ec_lib.c). Btw: if you frequently use multiplications
> > > where one point is the generator consider calling
> > > EC_GROUP_precompute_mult().
> >
> > Humm, EC_GROUP_precompute_mult(EC_GROUP, CTX) does not take a point as a
> > parameter how do you specify the point you want multiplied by the
> > g/generator/base point and where is the result stored?
>
> EC_GROUP_precompute_mult()  precomputes multiples of the generator.
> The precomputed values are stored in the EC_GROUP structure (in a
> EC_EXTRA_DATA object, see crypto/ec/ec_mult.c).
>
> Regards,
> Nils
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