Therefore, the community started an auditing process. Researchers reached out to Benedikt Bünz, lead author of the Bulletproofs paper, and to [OSTIF](https://ostif.org/) an organization which helps open source technologies to improve and secure themselves.
To accomplish this, two kind of ring signatures were constructed: One ring signature for the whole transaction (to prove the sum is 0), and a set of ring signatures for the subsets of transaction bits (to prove the outputs are positive numbers), then combined together using originally Schnorr signatures (and later replaced by Borromean ring signature).
