Tachyon and the Future of Private Transactions:

Implementing Out of Band Payments in Zcash and Other zk-SNARK Protocols

The Tachyon protocol, introduced by Sean Bowe, represents a groundbreaking evolution in privacy preserving payment technology.
Built upon years of cryptographic development in Zcash, Tachyon strips away complexity in favor of scalable, modular privacy while introducing powerful concepts like out of band payments, oblivious synchronization, and recursive SNARK aggregation.

https://tachyon.eco/

In this article, we will explore how Tachyon works, the implications of its design choices, and how it could be integrated into Zcash and other zk SNARK based protocols.

Tachyon is an upgrade compatible privacy protocol that reimagines shielded transactions by removing in band secret distribution. Unlike traditional Zcash implementations (Sapling, Orchard), where payment addresses and secrets are embedded and derived within the blockchain, Tachyon assumes that wallets interact out of band to handle payment metadata and secrets.

This design simplifies the shielded protocol dramatically, bringing it closer to the original Zerocash vision, while still preserving essential cryptographic guarantees from Orchard, such as:

  • RedPallas key re randomization
  • Homomorphic value commitments
  • Binding signatures
  • Delegation friendly key structures

Key Innovations and advantages: 

Out of Band Payments:

  • Privacy Benefit: No on chain leakage of payment metadata.
  • Implementation: Payment keys replace addresses; commitments are derived from shared secrets negotiated via URI or QR.
  • Result: Transactions are unlinkable, and the blockchain no longer stores information that could be correlated by adversaries.

Oblivious Synchronization

  • Concept: Users outsource synchronization proofs to untrusted services without revealing wallet state.
  • Privacy Benefit: Wallets reveal nothing but still prove that funds were valid.
  • Scalability: Validators only store recent nullifiers (e.g., last N blocks), dramatically reducing state bloat.

Simplified Notes and Nullifiers

  • Notes do not contain payment addresses or diversifiers.
  • Nullifiers are generated using simpler PRFs, no longer defending against “faerie gold” attacks due to out of band control.

Tachystamps and Aggregation

  • Tachystamps: Recursive SNARKs encapsulating shielded state changes.
  • Benefit: Entire blocks can be verified using a single SNARK.
  • Optimization: Authorizing data (signatures, keys) can be separated from data payloads.

This architecture enables fully private, recursive, and composable transactions.
Tachyon can be integrated in two primary ways:

Upgrade to the Orchard Pool:

  • Preserves existing infrastructure and shielded pools.
  • Requires tight coordination and soft/hard fork.
  • Enables backward compatibility.

Create a New Shielded Pool with Turnstiles:

  • Clean separation from legacy pools.
  • Requires migration tools.
  • Could reduce consensus overhead for older pools.

In either scenario, the changes are mostly modular:

  • zk-SNARK circuits will be simpler.
  • Wallets must be upgraded to handle out-of-band secret exchange (QR, URI, etc.).
  • New proof systems like Halo 2 or Nova could improve performance.

Tachyon’s model is also well suited for other privacy centric chains and apps:

Mina Protocol

  • Why It Fits: Native use of recursive SNARKs (Pickles) aligns with Tachystamps.
  • Use Case: Decentralized private apps with lightweight sync.

Aleph Zero / Nightfall

  • Why It Fits: Private smart contracts and enterprise-grade privacy.
  • Use Case: Enterprises could issue out-of-band private payments or grants.

Aztec (zk.money)

  • Why It Fits: Already uses out-of-band note sharing for L2 privacy.
  • Use Case: Replace complex note encryption trees with Tachyon-style commitments.

Tachyon’s model encourages:

  • Data minimization
  • Wallet independence
  • Stateless validators
  • Recursive scalability

Tachyon is not just a new shielded protocol. It is a vision for the future of private payments that are scalable, modular, and wallet centric. It is especially promising for:

  • Zcash, where protocol simplification is critical.
  • Emerging zk projects, looking to build efficient, auditable, and private systems.

As more chains adopt recursive SNARKs and wallet ecosystems mature, Tachyon provides a blueprint for integrating high assurance privacy without sacrificing performance or decentralization. The time for practical, scalable, and user respecting privacy is now, and Tachyon may be the spark.