proposal: crypto/elliptic: Make suggested alternative api more clear for ScalarMult

[zhiqiangxu]

Proposal Details

The Curve.ScalarMult is supposed to be deprecated according to here:

// ScalarMult returns k*(x,y) where k is an integer in big-endian form.
//
// Deprecated: this is a low-level unsafe API. For ECDH, use the crypto/ecdh
// package. Most uses of ScalarMult can be replaced by a call to the ECDH
// methods of NIST curves in crypto/ecdh.

But it's not very clear how to actually deprecate the ScalarMult call, and thus go-ethereum is still using this deprecated API:

secret, _ := crypto.S256().ScalarMult(cardPublic.X, cardPublic.Y, key.D.Bytes())

(source)

I don't think the rationale for deprecating this widely used method is very clear.

[gabyhelp]

Related Issues and Documentation

• Package elliptic > type CurveParams ¶ > func (*CurveParams) ScalarMult ¶
• Package elliptic > type CurveParams ¶ > func (*CurveParams) ScalarBaseMult ¶

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[seankhliao]

see #52221

It is not a goal of the standard library to support these operations.
You may continue to use deprecated functions.