Easier instantiation of Secp256k1

[JanBobolz]

For the protocol tutorial, I wrote the following code:

//Set up group and generate key
 var group = new LazyGroup(new Secp256k1()); //TODO can we make this easier somehow? Like maybe a GroupSuite or something? Like BilinearGroup has everything in one place.
 var H1 = new HashIntoLazyGroup(new Secp256k1.HashIntoSecp256k1(), group);

Can we make it easier to instantiate the Secp256k1 group (or - more generally - groups without pairings) ?
For BilinearGroup, you call one constructor and everything is immediately wrapped in the right (Lazy)Group and you have getters for the hash into the group.
Can we have something similar for non-bilinear groups? Like a GroupSuite that's basically a BilinearGroup for a single non-pairing group? Or maybe we make Secp256k1 a Singleton and have the getInstance() method return the (lazy-)wrapped GroupImpl by default. And/or maybe the Group interface gets a getHashIntoGroup(), i.e. the Group shall instantiate/know a proper hash function.

Looking for good ideas how to make sense of my rough ideas above and how to go about this the best way to make (non-pairing) groups and hashes easier to use in our library.

[rheitjoh]

Following the approach I used for the bilinear groups, we would create a new Secp256k1 class (add suffix Impl to old class) and make that extend LazyGroup. Similarly for the hash stuff. Then we can make the existing classes even package-private if we don't care about wrappers other than the lazy ones (or just add another class for basic group). I like that approach because it makes the user interface as simple as possible, i.e. just instantiate this class and off you go.

[feidens]

@JanBobolz thinks about it

[JanBobolz]

Quick and easy solution: add classes public class HashIntoSecp256k1 extends HashIntoLazyGroup and HashIntoSecp256k1Basic extends HashIntoBasicGroup.

Long-term nice (but less quick to implement) solution: add getHashIntoGroup to the Group interface.