Dev Sean joins the conversation as a cryptographer new to Zcash but with deep experience building recursive STARKs. Sean works on Zcash scaling and has been involved in the recent Project Tachion governance discussions.

The discussion covers Zcash's fundamental scaling challenges, particularly how current wallets must download every transaction to discover payments. This approach becomes unsustainable at higher transaction volumes, requiring innovative cryptographic solutions.

The conversation explores Private Information Retrieval (PIR) as a solution to payment discovery, Project Tachion's implementation timeline, quantum-resistant upgrades, and governance improvements. Both speakers emphasize Zcash's role as 'encrypted money' and peer-to-peer electronic cash with strong privacy guarantees.

Dev's Journey from STARKs to Zcash Privacy

Dev was inspired by Zcash from the beginning: 'It's kind of crazy. You can make a payment from person A to person B. Everyone in the world knows the payment's valid. No one knows who it's from, who it's to, or how much is in it.'

He built the first recursive STARK 8-9 years ago while working with Alessandro Chiesa at UC Berkeley, one of Zcash's founding scientists, focusing on making STARKs practical for recursion.

The key insight for recursion was that pre-processing SNARKs have constant additive overhead rather than multiplicative slowdown via simulation, making them practical for recursive verification.

After years working on DeFi scaling with Osmosis, Dev returned to privacy as 'the one thing that matters' as AI increases surveillance capabilities and 'the cost of surveillance just keeps dropping.'

The Fundamental Scaling Problem: Payment Discovery

Current Zcash wallets must 'test every single transaction on the blockchain' to discover payments, downloading ~100 bytes per transaction to check 'was this a payment to me or not.'

At 1000 TPS, this becomes '10 kilobytes a second' or 'gigabytes per day' of required downloads, making the approach completely unscalable for digital cash usage.

Out-of-band communication where 'Alice just tells Bob, hey, I paid you' works for active use but fails for recovery scenarios where 'Bob has forgotten everything and only has his 12 words left.'

The solution requires maintaining the core principle that users can recover funds with just their seed phrase and the blockchain, without depending on external services or data.

Private Information Retrieval: The Technical Solution

PIR allows clients to query a database without the server learning what key was requested - 'sounds kind of crazy' but enables private nullifier checking for spent detection.

For repeated payments between parties, Tachion introduces a new public 32-byte field that 'looks perfectly indistinguishable like it's a random 32 bytes' but contains deterministic tags from shared secrets.

After first contact and key exchange, parties can generate 'two streams of shared secrets. One's for transactions from me to you. A second one for transactions from you to me.'

With PIR, clients can privately query for their tags using 'about a megabyte of bandwidth' and 'two queries' to discover payments without downloading the entire blockchain.

Project Tachion's Overwhelming Community Support

The recent coin holder poll showed massive support with '1.1 million ZEC that voted' in favor versus 'just like seven ZEC that voted against it probably as a test.'

Sean interprets this as validation that 'scale matters to the project and the future of the success of the project. We need to scale not just with Tachion but with every other consensus work.'

The vote also demonstrated community resistance to 'compliance privacy' approaches, with ZSA proposals receiving less support from coin holders who prefer 'dumb money' over regulatory-friendly features.

Both developers emphasize that 'compliant privacy just can't exist' because 'if the data exists it's not private' - any backdoor compromises the fundamental privacy guarantees.

Quantum Resistance and Post-Quantum Roadmap

Zcash has a three-phase quantum resistance plan: quantum recoverable (funds can be recovered post-quantum), post-quantum private (encryption), and post-quantum sound (signatures and SNARKs).

Quantum recoverable pools can be added to Orchard 'without having to do any network upgrades' - it's 'such a simple wallet update' that mainly requires Keystone firmware updates.

Post-quantum addresses face a size problem where 'post-quantum public keys are like 10 kilobytes' making addresses 'look like a document, not like an address.'

The proposed solution involves posting full addresses on-chain with 'some burn amount' and creating a PIR database so users can still have '32 byte addresses again that will be post-quantum compatible.'

Governance Improvements and PIR Implementation

Current governance requires a 'registration period' where users must 'move your funds within a two-week horizon' due to technical limitations in proving unspent notes.

The new system eliminates registration by having servers build Merkle trees of all nullifiers, allowing users to prove non-inclusion with 'two queries and about a megabyte of bandwidth.'

Hardware wallet integration becomes seamless because users sign 'something very innocuous that cannot steal your money' rather than transactions that could drain funds.

This governance system will be 'the first use case of PIR in Zcash and to my knowledge blockchain as a whole,' making Zcash a pioneer in practical PIR deployment.

Ambitious Timeline and Dynamic Fees Challenge

Dev commits to getting 'the shielded protocol into mainnet' this year, acknowledging 'it's going to be ambitious and very difficult and I'm going to be stressed about it.'

Mid-summer targets include dropping block time 'from 75 seconds to 25 seconds' and consensus throughput '3xed' with Orchard TPS doubled for major UX improvements.

Dynamic fees are essential because 'there's some dollar cost' to saturate any fixed-fee network, but fee choices 'leak so much about you' and can distinguish wallet types.

The proposed solution involves committing to maximum fees with hotkey authorization for market rates, though this could increase transaction size 'from 9 kilobytes to 15' - a concerning 33% overhead.

Vision for Encrypted Digital Cash

Both developers emphasize everyday transaction usage: 'If you have lots of people engaging in commerce on the chain and all of their transactions are indistinguishable, everybody gains from the privacy.'

Dev describes Zcash as 'encrypted Bitcoin' and notes the cultural difference where Zcash users actually split bills and pay for meals with the protocol, unlike other crypto communities.

The goal is to fulfill Bitcoin's original vision as 'peer-to-peer electronic cash' while adding essential privacy: 'If I hand you $10, you have no idea where I got that $10 from. That's how the world has functioned for thousands of years.'

Success requires both technical scaling and cultural adoption: 'store value and keep on doing more and more payments' while fighting for continued relevance against quantum threats and governance challenges.