Add Mike Hamburg's analysis regarding the close-to-uniform hash2curve construction using elligator2 to the list of references

[BjoernMHaase]

There was presently no detailed analysis regarding indifferentiable hashing for the elligator2 construction in the reference list. Mike Hamburg has provided a corresponding analysis complementing the one from [BCIMRT10] for the case of Elligator2.

The Paper is currently available at https://www.shiftleft.org/papers/indifferentiable/ but Mike announced that he will be submitting it to the eprints.

[kwantam]

Note: ePrint is up at https://eprint.iacr.org/2020/1513