feat: update 121 (#183)

* feat: update 121

This update gives the results of the bulletproof+ audit.

* fix: small typos

_updates/2023-10-31-update-121.md

@@ -0,0 +1,94 @@
+---
+layout: update
+tag: Developer Update
+date: 2023-10-31
+author: CjS77   
+thumbnail: update-background.jpg
+title: Tari's Bulletproofs+ audit is done!
+subtitle: "Spoiler: It went pretty well."
+class: subpage
+---
+
+Tari uses an in-house implementation of the [Bulletproofs+](https://eprint.iacr.org/2020/735) range proving system to
+provide proofs that every (confidential) output in the UTXO set has a value between 0 and 2<sup>64</sup> μMinotari.
+
+This stops folks sending people negative amounts of Minotari, or trying other nefarious tricks to try and 
+inflate the Minotari supply in an undetectable way.
+
+Bulletproofs plus improves substantially on the original range proof algorithm that was originally used in Monero. 
+Bulletproofs+, as the name suggests, provides a set of incremental improvements over Bulletproofs.
+
+In particular, it supports:
+
+- **Proof aggregation**. You can generate a proof containing multiple range assertions in an efficient way.
+- **Extended commitments**. Commitments may contain multiple masks.
+- **Batch verification**. Verifying a set of multiple proofs is extremely fast.
+- **Minimum value promises**. You can prove that a commitment binds to at least a specified value.
+- **Mask extraction**. If the prover and verifier agree on a shared secret, the verifier can use it to recover the mask
+  used for the commitment in a non-aggregated proof.
+
+Compared to an [updated fork](https://github.com/tari-project/bulletproofs) of
+the `dalek-cryptography` [Bulletproofs](https://github.com/dalek-cryptography/bulletproofs) implementation, this
+Bulletproofs+ implementation is:
+
+- **Smaller**. Regardless of the aggregation factor, a Bulletproofs+ proof is 96 bytes shorter.
+- **Faster to generate proofs**. This implementation generates a non-aggregated 64-bit range proof about 10% faster,
+  with similar speedups for aggregated proofs. In fact, we're fairly sure that Tari BP+ implementation is now the 
+  _fastest trustless range proof system in the world_.
+- **Faster to verify single proofs**. This implementation verifies a single 64-bit range proof about 15% faster.
+- **Slower to verify aggregated proofs**. This implementation verifies aggregated proofs more slowly.  You can't win 
+  'em all.
+- **Faster to verify batched proofs**. Because this implementation supports batching, its marginal verification time for
+  a single 64-bit range proof can be reduced to _under half_ the corresponding non-batched time.
+
+## The audit
+
+The [Tari bulletproof+ library](https://github.com/tari-project/bulletproofs-plus) is a fairly small piece of Rust 
+code, but the math behind it is pretty complex. A bug in this code could lead to some catastrophic consequences for the
+Tari network. For this reason, we decided to partner with [Quarkslab](https://www.quarkslab.com/) to perform a 
+thorough review of the code and verify the correctness of the implementation.
+
+The audit was carried out between August and October 2023 and took around 4 weeks in total. 
+
+You can 
+
+* read the 
+**[full report](https://github.com/tari-project/bulletproofs-plus/blob/main/docs/quarkslab-audit/report.pdf)**
+* and read **Tari Labs' 
+[responses](https://github.com/tari-project/bulletproofs-plus/blob/main/docs/quarkslab-audit/README.md)** to the 
+  findings 
+
+in the Github repository.
+
+## I'm not reading an 80-page report! Just give me the results!
+
+Overall, the audit went very well. 
+
+The auditors found that the implementation was faithful to the underlying theory and that the optimisations were 
+cryptographically valid. 
+
+There was 1 `LOW` severity issue related to a dependency of the library that is no longer being maintained. 
+
+There were also two `INFORMATIONAL` level findings:
+* One was related to the library depending on a fork of the Dalek Ristretto library that has fallen a little out of 
+  date behind the main library. This is currently being addressed. 
+* The second informational issue was related to potential arithmetic overflow instances in parts of the code. These 
+issues have already been addressed and [resolved](https://github.com/tari-project/bulletproofs-plus/pull/62)  in the 
+latest version of the library.  
+
+## Acknowledgements
+
+This is a terrific result and is largely the work of long-time Tari contributors Aaron Feickert and Hansie Odendaal. 
+
+## What's next?
+
+The main Tari base node audit is wrapping up and the final report is due in the next few weeks.
+
+We're also waiting on the final report of the Aurora wallet penetration test.
+
+We will be announcing the results of those reviews in due course.
+
+
+
+
+