# Project Tachyon: Scaling Zcash with Proof-Carrying Wallets

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<img src="https://raw.githubusercontent.com/TheRhipper/Images/refs/heads/main/file_0000000006a462469eefcc3a38630375_conversation_id%3D68108e26-1b74-800c-92e3-199cd3c0ac36%26message_id%3D4c8b318e-e887-4dc8-ba8e-674bb80a14a4.png" style="max-width: 800px; width: 100%; height: 360px;" alt="Project Tachyon Header">
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Zcash has long led the frontier of blockchain privacy, enabling users to make shielded payments that remain invisible to the public eye. But as usage grows, so does the need for **scalability**.

Today, [Wallets](https://zechub.wiki/wallets) and validators face expensive synchronization costs, blockchain storage continues to grow without bound, and the dream of a truly scalable, private digital cash feels just out of reach.

**Project Tachyon** proposes a bold but carefully structured solution:
By rethinking how [Wallets](https://zechub.wiki/wallets) interact with the blockchain and how validators store shielded state, Zcash can **scale dramatically** — without compromising privacy.

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## The Current Bottleneck

Shielded Zcash transactions, based on cutting-edge [zk-SNARKs](https://zechub.wiki/guides/zero-knowledge-vs-decoys), ensure privacy — but at a cost:

- [Wallets](https://zechub.wiki/wallets) must scan every block, trial-decrypting thousands of transactions to find their funds.
- [Wallets](https://zechub.wiki/wallets) must maintain complex inclusion proofs to spend notes later.
- Validators must store every [Nullifier](https://zcash.github.io/orchard/design/nullifiers.html) ever published, forever preventing double-spends.
- The blockchain state grows endlessly, risking future scalability.

These challenges are the price of privacy — but with modern cryptography, we can now do better.

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## Project Tachyon: The Vision

Tachyon envisions a future where:

- [Wallets](https://zechub.wiki/wallets) prove the correctness of their own state as they synchronize.
- Transactions carry their own historical proofs of validity.
- Validators verify only *recent* activity, discarding old, unnecessary data.
- The blockchain becomes leaner, faster, and vastly more scalable.

The key innovation: using [Proof-Carrying Data (PCD)](https://hackmd.io/@lrusso96/HJUU4QlDY) at the [Wallet](https://zechub.wiki/wallets) level, paired with changes to transaction flow and blockchain state management.

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## Core Components of Tachyon

> ### 1. Out-of-Band Payments
>
> In today's Zcash, encrypted note data is broadcast inside transactions, forcing [Wallets](https://zechub.wiki/wallets) to download and attempt decryption of every shielded transfer.
>
> Tachyon moves note delivery **off-chain**, using secure external channels — such as messaging apps, encrypted storage, or QR codes — to share payment secrets.
>
> This reduces blockchain congestion and enhances user privacy.
>
>
>
> ---
>
> ### 2. Oblivious Wallet Synchronization
>
> Instead of checking every block, [Wallets](https://zechub.wiki/wallets) maintain a **self-updating proof** that their state remains valid.
>
> An **oblivious syncing service**, which learns nothing about [Wallet](https://zechub.wiki/wallets) contents, can update wallet state proofs even while the user is offline.
>
> This makes light wallets truly lightweight, while preserving trustless security.
>
>
>
> ---
>
> ### 3. Aggregated Shielded Transactions
>
> Using techniques long anticipated during [Orchard](https://zechub.wiki/using-zcash/shielded-pools)'s design, multiple shielded payments can be **aggregated** into a single [zk-SNARK](https://zechub.wiki/guides/zero-knowledge-vs-decoys) proof per block.
>
> This dramatically reduces verification costs and allows Zcash to support **larger, faster blocks**.
>
>
> ---
>
> ### 4. Improved Nullifier Derivation
>
> To prevent oblivious syncing servers from learning patterns, Tachyon proposes a subtle redesign of [Nullifier](https://zcash.github.io/orchard/design/nullifiers.html) generation.
>
> Instead of deriving [Nullifiers](https://zcash.github.io/orchard/design/nullifiers.html) from note commitments, the process is reversed, ensuring that syncing services cannot infer wallet activity or positions in the accumulator.
>
> This preserves the privacy shield even during third-party synchronization.
>
> ---
>
> ### 5. Efficient Accumulators
>
> Validators will batch [Nullifiers](https://zcash.github.io/orchard/design/nullifiers.html) into new accumulator structures that allow fast **set membership** and **non-membership** proofs.
>
> This enables historical [Nullifiers](https://zcash.github.io/orchard/design/nullifiers.html) and commitments to be **safely pruned**, keeping the blockchain slim and efficient.
>
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## The Path to Deployment

Tachyon is designed to roll out in **incremental, modular stages**:

| Phase | Upgrade | Immediate Benefit |
|:-----:|:---------------------------------|:-------------------------------|
| 1 | Out-of-band payment flows | Usability boost, zero risk |
| 2 | Transaction aggregation | Larger block capacity |
| 3 | New nullifier derivation | Private oblivious syncing |
| 4 | Accumulator integration | Enabling validator pruning |
| 5 | Wallet PCD integration | Full state scalability |

Each step improves capacity, security, or usability — **even before Tachyon is fully completed**.

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## Why Tachyon Matters

- **Scalability**: Unlocks orders-of-magnitude more shielded transactions.
- **Efficiency**: Light [Wallets](https://zechub.wiki/wallets) become truly lightweight.
- **Privacy**: Maintains Zcash’s world-class privacy guarantees.
- **Pruning**: Slashes blockchain bloat, future-proofs against growth.
- **Compatibility**: Designed to coexist with [Crosslink](https://forum.zcashcommunity.com/t/shielded-labs-crosslink-deployment-updates/49706), [ZSAs](https://zechub.wiki/zcash-tech/zcash-shielded-assets#content), and other initiatives.

In short: **Tachyon makes Zcash ready for millions of users.**

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> Source: [Tachyon: Scaling Zcash with Oblivious Synchronization](https://seanbowe.com/blog/tachyon-scaling-zcash-oblivious-synchronization/)

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