bitcoinjs-lib and related repos are not 100% RFC6979 compliant (only 99.999...%)

[dabura667]

Okay, the r=0 (are there points on secp256k for x=0?) or s=0 is another (unlikely to occur) problem.

R.x == 0 is not a point on the curve; but R.x congruent to 0 (mod order) _is_ on the curve, and so r can be zero because r is the x value of R mod the curve order.

(And likewise, s can be zero; e.g. I have a test in libsecp256k1 for s==0:
https://github.com/bitcoin/secp256k1/commit/8d11164bc0e03024d38d5694e81f334ea31ec238#diff-4655d106bf03045a3a50beefc800db21R1210)

I was gonna flip a nut because I thought you meant you found an RFC6979 compliant k, z, and da that would calculate out to s = 0.

Then I saw you just set k to 1, da to 1, and z to the complement to generator's x coord, and I had one of those moments like when your parents tell you you're going to the toy store and you end up at the dentist.