code: public static ECP weakBBSign(BIG sk, BIG m) {
          BIG exp = IdemixUtils.modAdd(sk, m, IdemixUtils.GROUP_ORDER);
          exp.invmodp(IdemixUtils.GROUP_ORDER);
  
          return IdemixUtils.genG1.mul(exp);
      }
docs: Produces a WBB signature for a give message
  
  @param sk Secret key
  @param m  Message
  @return Signature