Ch.4 derive y from x

[jl2012]

After y is derived from x, you need to verify that (x,y) is a valid point of the curve

https://github.com/bitcoin-core/secp256k1/blob/master/src/field_impl.h#L130

[smh69]

after derivation of y via x and the curve params, as long as it's done correctly, is it not true that the point must necessarily be on the curve? or am i missing edge cases?

[jl2012]

If and only if x is a valid x

[jimmysong]

Oh, good point. Thanks for bringing it to my attention!

[jimmysong]

Turns out that the Point class will test to see if (x,y) is on the curve so this is not a problem.