group like the NIST curves we support is // cryptographically negligible. If we hit it, something is awfully wrong. if r.IsZero() == 1 { return nil, errors.New("ecdsa: internal error: r is zero") } e := bigmod.NewNat() hashToNat(c, e, hash) s, err := bigmod.NewNat().SetBytes(priv.d, c.N) if err != nil { return nil, err } s.Mul(r, c.N) s.Add(e, c.N) s.Mul(kInv, c.N) // Again, the chance of this happening is cryptographically negligible. if s.IsZero() == 1 { return nil, errors.New("ecdsa: internal...