Make use of the secp256k1 endormorphism #1
Description
The sec256k1 curve has an efficiently computable endomorphism which can be used to speed up the scalar point multiplications. See section 3.5 of Guide to Elliptic Curve Cryptography - Hankerson, Menezes, Vanstone for details.
btcec should be modified to make use of the endomorphism for further speedup.