implement hash to group function

[zhenfeizhang]

We have not encountered a case where hash to group is necessary. So this is a low priority for now.

We may consider implement

• rejection sampling based, or
• Hash to Elliptic Curve implementation of https://datatracker.ietf.org/doc/draft-irtf-cfrg-hash-to-curve/

[alxiong]

now arkworks already have HashToCurve implementation, correct? should we close this? @zhenfeizhang

[tessico]

Should be closed as soon as arkworks v0.4 migration: https://github.com/EspressoSystems/jellyfish/issues/45 is completed.

[mrain]

Shall we close this ticket and create a new one for constant time hash to bn254 curve? cc @alxiong @chancharles92

[chancharles92]

@alxiong mentioned that arkworks v0.4 already has a hashtogroup implementation. Is it a naive one or something we can reuse?

[alxiong]

Yes, arkwork defined the trait HashToCurve here, and implement it here with flexibility for different hashing and mapping (from field to group) strategies.

I think we can close it for now.

(ofc, if we want constant time in a separate issue/PR, consider building on top of subtle or subtle-ng)