ecdh(local *PrivateKey, remote *PublicKey) ([]byte, error)

	// privateKeyToPublicKey converts a PrivateKey to a PublicKey. It's exposed
	// as the PrivateKey.PublicKey method.
	//
	// This method always succeeds: for X25519, the zero key can't be
	// constructed due to clamping; for NIST curves, it is rejected by
	// NewPrivateKey.
	privateKeyToPublicKey(*PrivateKey) *PublicKey
}

		return nil, errors.New("crypto/ecdh: invalid private key size")
	}
	return &PrivateKey{
		curve:      c,
		privateKey: append([]byte{}, key...),
	}, nil
}

func (c *x25519Curve) privateKeyToPublicKey(key *PrivateKey) *PublicKey {
	if key.curve != c {
		panic("crypto/ecdh: internal error: converting the wrong key type")
	}
	k := &PublicKey{
		curve:     key.curve,
		publicKey: make([]byte, x25519PublicKeySize),

	k := &PrivateKey{
		curve:      c,
		boring:     bk,
		privateKey: append([]byte(nil), privateKey...),
	}
	return k, nil
}

func (c *nistCurve[Point]) privateKeyToPublicKey(key *PrivateKey) *PublicKey {
	boring.Unreachable()
	if key.curve != c {
		panic("crypto/ecdh: internal error: converting the wrong key type")
	}
	p, err := c.newPoint().ScalarBaseMult(key.privateKey)