Saturday, June 22, 2024

A glance again: NU5 and community sandblasting


As Electrical Coin Co. (ECC) and the Zcash group put together for public retrospectives of zcashd Community Improve 5 (NU5) and what has turn into generally known as the sandblasting assault, this weblog submit particulars ECC’s motivations, challenges, and accomplishments with regard to every. 

  • The NU5 improve was an formidable endeavor to remove the necessity for trusted setups, improve person confidence, and improve Zcash’s safety and scalability.
  • The implementation of Halo, a cryptographic breakthrough, on Zcash made potential trustless, personal, digital-cash transactions for the primary time on cellphones.
  • A malicious assault following the improve led to important pockets efficiency points, prompting ECC to enter Emergency Mode. Our response concerned a number of technical updates, efficiency enhancements, and the discharge of recent mobile-wallet SDKs.
  • Regardless of the challenges and delays, ECC succeeded in bettering the safety and resiliency of Zcash.

Public retrospective: Wednesday, Dec. 13 at 22:00 UTC/17:00 EST

What the FUD?

ECC’s mission is to empower financial freedom, and most organizations that work on Zcash-related tasks, just like the Zcash Basis (ZF) and Zcash Group Grants (ZCG), have related community-minded aims for the betterment of humanity. 

However, since Zcash got here into the world in 2016 a stream of misinformation (and a few coordinated propaganda) has been circulated on social media, boards, and different group platforms meant to incite FUD (concern, uncertainty, and doubt).

The rumors claimed that Zcash was compromised, or that it was weak to counterfeiting, or that there was a backdoor that will enable third events to entry a person’s transaction data with out their consent. 

And sadly, till NU5 was launched, there was a serious impediment in confronting these assaults: the trusted setup. When Zcash launched, its zero-knowledge proofs required a Ceremony, or trusted setup section, to provide public parameters that allowed customers to assemble and confirm personal transactions.

This system was pioneered by ECC, and it required a number of events in numerous areas utilizing complicated safety measures.

Whatever the extra-careful planning and execution plus redundant safety, Zcash customers and observers needed to belief the historic incontrovertible fact that the ceremony members weren’t conspiring to deceive the general public. Trusted setups don’t enable for a mathematically verifiable provide, and so long as these difficult procedures have been required for main Zcash upgrades, there would at all times be doubters and detractors. And the doubters would have some extent — arithmetic is verifiable, however historical past isn’t. The fame and integrity of Zcash was being challenged, and in ECC’s view, this was a problem the group couldn’t afford to disregard.

NU5: A name to motion

In 2019, ECC engineers Sean Bowe, Daira Emma Hopwood, and Jack Grigg had been engaged on scalability design and experimenting with an answer for environment friendly recursion when Bowe made a discovery.

“I simply stumbled upon a method to do that zero-knowledge proof development on utterly strange elliptic curves,” Bowe mentioned. “And so over the course of perhaps 24 hours, it went from, ‘Ooh, that’s actually thrilling, that’ll be neat if we will try this’ to ‘Holy crap, now that we don’t have trusted setups or something, it’s all actually easy. It was a sequence of steps that turned from a pleasant perception into a whole paradigm shift.”

Halo, as it could come to be recognized, is a zero-knowledge proving system that permits recursion with out a trusted setup in an environment friendly method. 

Bowe’s discovery was a cryptographic breakthrough heralded by the business, and in 2021 ECC dedicated to implementing Halo in Zcash.

Halo on Zcash would make trustless, personal, digital-cash transactions potential for the primary time on cellphones. It could function a catalyst for Zcash person confidence and supply a path to a lot higher scalability, whereas making the protocol extra engaging, sooner, and cheaper for others to construct on. 

From the ECC weblog: 

Halo on Zcash would allow circuit upgrades with out the necessity for trusted setups, making the Zcash shielded protocol extra agile for future enhancements, comparable to supporting extra belongings like [Zcash Shielded Assets, or ZSAs]. We wish to make it simple for different tasks and tokens to profit from Zcash options, comparable to privateness by encryption. Trusted setup will turn into a remnant of the previous.

As well as, this improve would pave the best way for shielded Zcash scale by proof aggregation and blockchain succinctness, two scalability enhancements. This is able to enhance the person expertise by eliminating irritating synchronization time that plagues all blockchains as we speak, lowering the standard blockchain bloat, and permitting for non-escalating charges as utilization will increase. In conversations with giant social platforms who expressed curiosity in native Zcash assist, a viable path to scalability was given as a requisite near-term consideration.

In January 2021, after greater than a 12 months of Halo R&D, ECC concluded that the advantages of Halo on Zcash outweighed different protocol priorities, and we proposed implementing it in NU5. 

Watch the Zcash Media video concerning the authentic Ceremony, its members (together with Edward Snowden), and the way Halo makes trusted setups out of date.

NU5 aims and obstacles

Our NU5 objectives from the outset have been to (1) make Zcash safer, (2) give Zcash customers confidence by making the provision mathematically verifiable, (3) make future upgrades simpler, and (4) allow future upgrades to profit from recursive proofs for scalability and programmability enhancements.

Our authentic estimate of 6-7 months turned out to be overly optimistic — as new discoveries have been made, alternatives have been revealed within the course of, and technical complexities arose — and ultimately the journey took nearly a 12 months and a half.

Alongside the best way, we confronted quite a lot of technical challenges. For instance, the complexity of together with Orchard assist within the zcashd embedded pockets was not correctly accounted for within the authentic estimates for the NU5 timeline. 

ECC confronted time-consuming engineering hurdles, like constructing a sophisticated circuit for Halo-plus-Orchard to make it work on cell gadgets. And midstream, we made the choice to implement unified addresses (UAs) to allow shielded by default in supporting wallets. The design and build-out of UAs have been tough, and if ECC had been working towards product-driven planning and improvement on the time (like we at the moment are) we imagine we might have recognized the necessity for UAs sooner and their implementation would have been smoother.

Along with battling technical obstacles like these, plus a number of shock bugs, ECC spent important time and sources advocating for and defending our roadmap choices towards criticism for: our rationale (eliminating trusted setup wasn’t definitely worth the effort and time, ZSAs have been extra vital), our planning (we kicked off the dialogue publicly earlier than planning sufficient -and- we deliberate an excessive amount of earlier than beginning the work), the choice to license Orchard underneath the Bootstrap Open Supply Licence (BOSL), the choice to implement Unified Addresses (UAs), and our total method to community upgrades (our priorities have been arbitrary and out of contact).

It’s vital to acknowledge that we had important group assist throughout the course of, too. Total, group sentiment was constructive. We acquired precious perception and suggestions from our Scientific Advisory Board and essential safety audits from Qedit and NCC group.

NU5 timeline and accomplishments

Not together with the pre-implementation analysis and improvement, NU5 was a 17-month endeavor that delivered novel expertise and improved Zcash person expertise. 


When Zcash NU5 activated on mainnet Could 31, 2022, it was one of the vital milestones for Zcash for the reason that cryptocurrency launched in 2016. As ECC CEO Zooko Wilcox put it, “an historic step ahead for human society.” 

In launching the Orchard shielded fee protocol using Halo, we eradicated the trusted setup to enhance Zcash safety and sustainability, made the provision mathematically verifiable, improved scalability as a result of future community upgrades received’t require a sophisticated setup ceremony, paved the best way for elevated interoperability by offering a system that might unlock personal cross-chain proofs at scale, and launched BOSL which has returned worth to the Zcash group (e.g., Filecoin Basis and Ethereum Basis grants to Courageous and Edge).

It was a large effort, and after nearly a 12 months and a half of constructing and wrestling with the technical challenges of NU5, the ECC Core staff was prepared for some relaxation. However nearly straight away, Zcash was hit with one other situation we couldn’t ignore.

The sandblasting assault

In June 2022, nearly instantly after ECC launched NU5, a major problem emerged. The Zcash community started experiencing an enormous improve in shielded transaction measurement and exercise. This extra community load brought on a “knowledge pileup” that prevented some wallets (Nighthawk, Edge, and Unstoppable) from with the ability to sync in an inexpensive period of time. Wallets weren’t syncing and a few customers weren’t capable of entry their funds.

This was an issue that ECC, as the first maintainer of zcashd and provider of mobile-wallet SDKs, was best-positioned to confront.

Sandblasting assault: A name to motion

Some events at ECC didn’t initially wish to make the belief that this uncommon transaction load was the work of a malicious actor. Ultimately nonetheless, the proof that it was a malicious actor turned overwhelming — and we’ve purpose to imagine it might even have been coordinated by the identical actor or group of actors who unfold Zcash FUD, and that they might have been paid to take action.

However fixing that thriller was much less vital than fixing the issue. 

Sandblasting assault: Targets and obstacles

Our prime precedence was guaranteeing customers may regain entry to and spend their ZEC (Zcash cash). That is elementary to our mission of financial freedom and a requirement for real-world, personal digital money.

As an preliminary line of protection, we launched  efficiency enhancements in zcashd 5.1.0 and 5.2.0 to scale back verification time by as much as 80%. We additionally started engaged on efficiency upgrades to our cell pockets SDKs.

In August 2022, with numerous work left to unravel these pockets efficiency points, ECC went into Emergency Mode. This was our standards for exiting Emergency Mode:

  • Customers of Edge, Nighthawk, and Unstoppable can spend their present funds (funds which can be already synced once they open their pockets).
  • Customers of these wallets can obtain and turn into capable of spend new incoming funds at a price of a month’s value of transactions in 1 hour.
  • Customers of these wallets see sync updates that are minimally complicated about progress.
  • None of these wallets are impacted by frequent crashes or inconsistent conduct (comparable to failing to show some already synced transactions), nor do they require work-around behaviors because of the ECC SDK.

The pockets efficiency points introduced a sophisticated sequence of challenges to handle, they usually required growing and implementing (1) a sooner algorithm that doesn’t require a linear sync of all blocks on chain and (2) tooling modifications that will give customers the flexibility to spend funds with out having a totally synced chain. The answer required modifications to each part within the shielded cell pockets stack: zcashd, lightwalletd, the ECC pockets SDKs, and the ECC prototype pockets.

Internally, price modifications have been debated from the get-go, however for the primary few months, the ECC staff targeted on extra efficiency enhancements and labored to resolve the problem with out price modifications. Later, we determined to implement price modifications to throttle the spam assault.

As customers turned annoyed with their person expertise, some group members turned vocal and publicly criticized ECC for not being ready for the assault and sluggish to reply.

In February 2023, we have been notified by blockchain safety agency Halborn of vulnerabilities inherited from Bitcoin Core which will have affected greater than 280 chains, together with Zcash. This was one other all-hands-on-deck emergency on prime of the pockets efficiency points, and as ECC was the one staff notified of the vulnerability, we have been the one ones who may make the mandatory fixes. The coordination of the disclosure and remediation consumed roughly a month of our time.

To make issues worse, ECC as an engineering group was making an attempt to do too many issues directly: core node upkeep, supporting CEXes like Coinbase, Binance, and Gemini, backports from Bitcoin, cell SDKs, cell pockets purposes, and future protocol enhancements. ECC restructured in Could 2023, which additional strained sources quickly.

Further challenges

  • On the time, ECC inner communication and undertaking administration practices weren’t organized for an Emergency Mode state of affairs. This affected our understanding of priorities and workflow throughout groups.
  • Earlier than the assault, ECC product technique targeted on adoption first, as an alternative of efficiency and scalability. Customers need new options, and dealing on bettering efficiency slows function releases. However the assault took Zcash UX to the bounds instantly.
  • Technical debt: We had applied earlier community upgrades with solely restricted efficiency enhancements.
  • ECC vastly underestimated how lengthy it could take to repair excellent pockets efficiency points.
  • Different technical points arose that brought on delays, comparable to when bitrotted after which obtained deleted whereas ECC was with out a devops supervisor. 
  • The ECC Core staff had three completely different managers throughout Emergency Mode.
  • Emergency Mode slowed improvement of our deliberate pockets product, now generally known as Zashi. Nonetheless, we have been capable of leverage the prototype internally to validate and take a look at SDK enhancements.

ECC was fortunate to have proactive pockets companions — Edge, Nighthawk, and Unstoppable — who labored with us to check releases and submit bugs, then have been fast to implement SDKs 2.0 once they have been prepared.

Sandblasting assault: Timeline and accomplishments

In all, ECC’s sandblasting response and implementation by third-party wallets consumed about 16 months. By November 2023, Edge, Nighthawk, and Unstoppable have been working once more (higher than ever), and we introduced an finish to Emergency Mode.


  1. June 2022: Community spamming started; shielded outputs jumped from a month-to-month common of 42,600 to 21,622,590 in June alone
  2. July 2022: Carried out efficiency enhancements in zcashd 5.1.0 and 5.2.0 to scale back verification time by as much as 80% and started engaged on efficiency enhancements to our cell pockets SDKs
  3. August 2022: ECC formally entered Emergency Mode, though we didn’t use that time period in public written communications till March 2023; began researching Spend Earlier than Sync
  4. September 2022: Whereas engaged on zcashd and improved cell sync expertise, re-opened analysis into potential price change mechanisms (ZIP 317) and syncing efficiencies (DAGSync/Spend Earlier than Sync)
  5. October 2022: Launched zcashd 5.3.0 with extra efficiency enhancements to scale back concurrent reminiscence utilization throughout scanning amongst different reminiscence and efficiency associated optimisations within the zcashd node
  6. October 2022: Reaffirmed our instant aims relating to syncing points with our pockets SDKs and communicated our standards for exiting Emergency Mode
  7. October 2022: Communicated our intent to have pockets efficiency points resolved by the tip of February 2023
  8. October 2022: Modifications to zcashd elevated its robustness towards the assault
  9. November 2022: Recognized and stuck the final recognized bugs that have been blocking the primary section of SDK releases, continued progress on Spend Earlier than Sync, and started prepping each zcashd and cell wallets for ZIP 317; squashed the final recognized librustzcash bugs that have been blocking pockets launch and accomplished Android & iOS SDK integration
  10. December 2022: Accomplished the implementation of zcashd optimizations anticipated to save lots of reminiscence and to scale back orphan charges for miners
  11. February 2023: Launched zcashd 5.4.0 to introduce quite a lot of efficiency enhancements, an replace to appropriate provide reporting, and a clear up of legacy options and assist performance to enhance ongoing upkeep of the codebase
  12. March 2023: Printed an replace and launch schedule calling for an finish to Emergency Mode by the tip of Could
  13. April 2023: ECC launched 5.5.0 with the finished transaction-fee-structure change (ZIP 317) and infrastructure enhancements that laid the groundwork for five.6.0.
  14. Could 2023: (Restructuring at ECC) Pushed the discharge date for zcashd 5.6.0, lightwalletd, and SDKs to mid-June. As zcashd 5.5.0 started to be adopted by miners on the community, the price construction modifications started to blunt the efficacy of the sandblasting assault, lowering the speed of blockchain development and pockets scanning load.
  15. June 2023: Launched zcashd 5.6.0, introducing the performance crucial for gentle wallets to entry spendable funds with out totally scanning the blockchain; included updates to handle points associated to the ZIP-317 implementation and privateness coverage options.
  16. July 2023: Lightwalletd 0.4.14 was launched, which meant the cell pockets SDK was the one excellent piece in ECC’s plan to resolve pockets efficiency points and exit Emergency Mode. At this level, we had hoped to launch the SDKs in mid-July.
  17. August 2023: By the tip of July, the adoption of zcashd 5.5.0 by the community was full, and community transaction load had returned to pre-NU5 ranges. Nonetheless, the amassed chain knowledge thus far nonetheless introduced an issue for pockets scanning, and so to mitigate this situation ECC introduced the pre-release availability of the Spend earlier than Sync functionality in our cell SDKs and made this performance out there to pockets builders for testing. A number of bugs and UX points have been found. Timeline for the SDK releases was shifted to mid-September.
  18. September 2023: New bugs, UX points, and dependencies arose that pushed the SDKs launch date out to the tip of September.
  19. Sept. 26, 2023: ECC launched the up to date cell SDK 2.0 for each iOS and Android builders. This was the ultimate deliverable for exiting Emergency Mode.
  20. Nov. 1, 2023: After a month in manufacturing, no associated, main pockets points have been reported and ECC declared an exit from Emergency Mode.

The fruits of our sandblasting response was that third-party Zcash wallets have been working once more, and future attackers have been additional deprived. 

Throughout this time, ECC launched a number of updates to zcashd and lightwalletd, plus new cell SDKs that, collectively, launched new improvements (and studying) on this planet of cryptography and decentralized cash. These releases present large upgrades to privateness, scalability, and person expertise in Zcash, they usually have implications for all privacy-focused crypto tasks.

The work continues

NU5 and the sandblasting assault consumed almost three years. However confronted with organized adversity, competing emergencies, and group criticism (a few of it warranted), ECC didn’t stray from our dedication to construct. With allies alongside the best way, the group overcame unprecedented technical challenges and useful resource constraints to make Zcash extra resilient, dependable, and protected.

We discovered so much, and though we’d like to step again and take a break, we all know the work is extra vital now than ever. We look ahead to distilling the teachings from these experiences within the upcoming retrospective, and we’re honored to proceed the hassle to construct for financial freedom and a world-class Zcash person expertise.

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