multiplication of point does not match other open source library

[grantwest]

btcd and lnd both use this function for multiplying a public key point by a private key:
https://github.com/btcsuite/btcd/blob/master/btcec/btcec.go#L758

This library sometimes produces a different result than the btcsuite implementation. For example:

test "mult that fails" do
  k = bin("1111111111111111111111111111111111111111111111111111111111111111")
  x = 31855367722742370537280679280108010854876607759940877706949385967087672770343
  y = 46659058944867745027460438812818578793297503278458148978085384795486842595210
  p = Secp256k1.Point.new(Secp256k1.Secp256k1Curve, x, y)
  p = Secp256k1.Point.mult(p, as_uint(k))
  assert p.x == 54221562124304953885180771592460698670019519428706259911404568629517370541567
  assert p.y == 41503598524832693408649273746083320222793867734891856875367632750649152059192
end

test "mult that passes" do
  k = bin("1212121212121212121212121212121212121212121212121212121212121212")
  x = 63982838722979151810905110027192376571325135238113748936948631759147324327927
  y = 17180151785156071809562681746353818655281144606192631545001595874213337763680
  p = Secp256k1.Point.new(Secp256k1.Secp256k1Curve, x, y)
  p = Secp256k1.Point.mult(p, as_uint(k))
  assert p.x == 111804478433660530705186081768070827849460643277644950589351528573593999580785
  assert p.y == 60380851274475674924967971953847652042604723681086380245173273372347822570512
end

def as_uint(<<i::unsigned-size(256)>>), do: i

defp bin(h) do
  Base.decode16!(h, case: :lower)
end

You will notice that in the failing example the y point that the elixir implementation is returning is negative. I think all results are supposed to be positive.

[spscream]

@grantwest thanks, i'll check this

[leeduckgo]

👍Same Problem and fixing it by myself……