SWU when A=0 in curve equation?

[cygnusv]

Current version of the draft asserts the following with respect to the SWU method:

This algorithm works for any curve over F_{p^n}

Every elliptic curve can be converted to an equivalent curve in short Weierstrass form ([BL07] Theorem 2.1), making SWU a generic algorithm that can be used for all curves

However, the SWU method (and its simplified version) require the computation of -B/A, which is undefined when A=0.

This is related to #9 and #39, since it's a problem for curve SECP256K1, with curve equation y^2 = x^3 + 7 (i.e, A=0 and B=7).

[samscott89]

Thanks, good catch. We will make sure to address this in the next version.

[samscott89]

Covered in #72