Architecture

What is NEXUS?

NEXUS is a unified smart contract execution layer for proof-of-work blockchains. It adds programmability to Zcash first, with Bitcoin and Dogecoin joining the same execution layer as it expands. NEXUS is a metaprotocol — it has no separate chain. It reads Zcash (and later Bitcoin/Dogecoin) transactions, processes them according to NEXUS rules, runs WASM smart contracts, and writes a state summary back to those same chains. The underlying L1 never changes; NEXUS just gives it superpowers.

New to blockchain terms? See the Glossary for plain-English definitions of L1, WASM, ZK proofs, vaults, and more.

V1 vs V2 — What’s Available Now

Feature	V1 (Live on Zcash)	V2 (Planned)
Smart Contracts (WASM)	✅ Zcash	✅ + Bitcoin + Dogecoin
ZEC Deposits & Withdrawals	✅	✅
BTC Deposits & Withdrawals	🔄 Coming soon	✅
DOGE Deposits & Withdrawals	🔄 Coming soon	✅
Stealth Addresses	✅	✅
Encrypted Mempool (MEV protection)	✅	✅
Zcash Shielded Withdrawals (z-addr)	🔄 Coming in V2	✅
Cross-Chain Swaps (ZEC ↔ BTC ↔ DOGE)	❌	✅
Unified Liquidity Pools	❌	✅

Core Components

┌─────────────────────────────────────────────────────────────────┐
│                      NEXUS Metaprotocol                         │
├─────────────────────────────────────────────────────────────────┤
│                                                                  │
│  ┌──────────────────────────────────────────────────────────┐   │
│  │              Execution Layer (processes transactions)     │   │
│  │  ┌─────────────┐  ┌─────────────┐  ┌─────────────┐       │   │
│  │  │  WASM VM    │  │  State      │  │  Encrypted  │       │   │
│  │  │  Executor   │  │  Processor  │  │  Mempool    │       │   │
│  │  └─────────────┘  └─────────────┘  └─────────────┘       │   │
│  └──────────────────────────────────────────────────────────┘   │
│                                                                  │
│  ┌──────────────────────────────────────────────────────────┐   │
│  │           Bridge Layer (connects to each chain)          │   │
│  │  ┌────────────────────┐  ┌──────────┐  ┌──────────┐      │   │
│  │  │  Zcash Bridge      │  │  Bitcoin │  │ Dogecoin │      │   │
│  │  │  ✅ Live           │  │  🔄 Soon │  │ 🔄 Soon  │      │   │
│  │  └────────────────────┘  └──────────┘  └──────────┘      │   │
│  └──────────────────────────────────────────────────────────┘   │
│                                                                  │
│  ┌──────────────────────────────────────────────────────────┐   │
│  │                   Security Layer                          │   │
│  │  ┌─────────────┐  ┌─────────────┐  ┌─────────────┐       │   │
│  │  │  ZK Proofs  │  │   Fraud     │  │  Economic   │       │   │
│  │  │   Groth16   │  │   Proofs    │  │   Bonds     │       │   │
│  │  └─────────────┘  └─────────────┘  └─────────────┘       │   │
│  └──────────────────────────────────────────────────────────┘   │
│                                                                  │
└─────────────────────────────────────────────────────────────────┘

Execution Layer

WASM Virtual Machine (Smart Contract Engine)

NEXUS runs smart contracts written in Rust, compiled to WebAssembly (WASM) — a compact, portable binary format. The VM:

Runs the same contract code identically on every node
Charges gas for each operation (prevents runaway code)
Provides contracts access to storage, events, L1 chain data, and cross-contract calls
Today runs on Zcash; the same VM will execute contracts anchored to Bitcoin and Dogecoin when those chains join

State Processor

The state processor maintains the global record of all contract state and balances. It:

Processes transactions in order
Computes a state root — a single hash summarizing all state
Posts that root to Zcash L1 so anyone can verify NEXUS is behaving correctly
When Bitcoin/Dogecoin join, state roots are committed to all live chains simultaneously

Encrypted Mempool

Transactions are encrypted before submission using ECDH + ChaCha20-Poly1305. Their contents are hidden from miners until a block is produced. This prevents MEV (front-running and sandwich attacks). Protocol version 2. Domain: nexus-encrypted-mempool-chacha20poly1305-v2. See Encrypted Mempool for details.

Fee Market (EIP-1559 Style)

NEXUS uses a dynamic fee system:

A base fee adjusts automatically — rises when blocks are full, falls when empty
Maximum change per block: ±12.5% (smooth, predictable)
Target utilization: 40% of block gas
On Zcash: fees are denominated in zatoshi. Base fee: 244,000,000 zatoshi/gas unit
Add a priority tip for faster inclusion

Bridge Layer

Each chain has a dedicated bridge that monitors deposits, processes withdrawals, and posts state commitments to L1.

Zcash Bridge ✅ Live

Vault type: Transparent address (t-addr), P2SH 2-of-2 multisig (you + protocol)
Verification: Groth16 ZK proofs — verified natively by Zcash nodes. No external verifier needed.
State commits: Posted as Sapling shielded notes — not OP_RETURN. Each epoch writes a shielded note with a 512-byte encrypted memo containing the full state metadata. Epochs are linked via nullifiers, forming a cryptographically verifiable chain from genesis.
Deposit confirmations: 10 blocks (~12.5 min at 75s/block)
Escape timelock: 16,128 blocks (~2 weeks)

Why Sapling notes instead of OP_RETURN? Sapling memos hold 512 bytes (vs 80 bytes for OP_RETURN), nullifiers prevent state replay, and Zcash natively verifies the cryptography. Anyone with the public Full Viewing Key can independently verify all NEXUS state history on Zcash.

Bitcoin Bridge 🔄 Coming soon

Vault type: Taproot (P2TR) with escape hatch
Verification: ZK-STARK proofs + BitVM2 bisection fraud proofs
State commits: OP_RETURN outputs (32-byte state root)
Deposit confirmations: 6 blocks (~60 min)
Escape timelock: 2,016 blocks (~2 weeks)

Dogecoin Bridge 🔄 Coming soon

Vault type: P2PKH with CLTV escape hatch
Verification: ZK-STARK proofs + fraud proofs
State commits: OP_RETURN outputs
Deposit confirmations: 3 blocks (~3 min — Dogecoin’s 1-minute blocks are the fastest)
Escape timelock: 20,160 blocks (~2 weeks)

Security Layer

How NEXUS Ensures Correctness

Two independent security mechanisms protect NEXUS on Zcash: 1. Cryptographic proofs (Groth16 ZK) Before posting state, the operator generates a Groth16 proof that all transactions were processed correctly. Zcash nodes verify this natively — the same cryptography Zcash uses for shielded transactions. If the proof is invalid, Zcash rejects it outright. 2. Economic bonds + fraud proofs Operators post a bond in ZEC before committing state. If the commitment is wrong, anyone can challenge:

Challenger detects an incorrect state commitment
Challenger posts a bond and opens a challenge
Bisection game narrows down to the single bad computation step
That step is verified on-chain via Groth16
The fraudulent operator loses their bond to the challenger

Both mechanisms must fail simultaneously for any attack to succeed.

Verification by Chain

Chain	Proof System	Who Verifies	Status
Zcash	Groth16 (native on-chain)	Zcash nodes automatically	✅ Live
Bitcoin	ZK-STARK + BitVM2 bisection	Anyone (permissionless)	🔄 Coming soon
Dogecoin	ZK-STARK + fraud proofs	Anyone (permissionless)	🔄 Coming soon

Vault Architecture

Every user’s deposited funds are held in a vault — an on-chain address with two spending paths:

Vault Address (Zcash t-addr, P2SH 2-of-2)
│
├── Normal Path — you + NEXUS together
│   └── Instant withdrawal — processed by the protocol
│
└── Escape Path — you alone, after ~2 weeks
    └── Safety exit — no permission needed, works even if NEXUS stops

The escape path ensures your funds are always recoverable. NEXUS cannot unilaterally spend from your vault — it needs your key.

Escape Hatch Waiting Periods

Chain	Blocks	Time	Why
Zcash	16,128	~2 weeks	16,128 × 75s = 14 days
Bitcoin	2,016	~2 weeks	2,016 × 10min = 14 days
Dogecoin	20,160	~2 weeks	20,160 × 1min = 14 days

Privacy Layer

NEXUS ships two privacy features in V1, live on Zcash: Stealth Addresses — Generate a unique one-time address per transaction. Observers cannot link multiple transactions to the same wallet. Uses ECDH + HKDF-SHA256 with 1-byte view tags (filters 99.6% of non-matching scans). See Stealth Addresses. Encrypted Mempool — Transactions encrypted before submission. Miners cannot read contents until after inclusion. Prevents MEV. See Encrypted Mempool.

Transaction Flow (on Zcash)

Deposit

You request a vault address → SDK or CLI returns a Zcash t-addr
You send ZEC to that address
NEXUS scanner detects deposit after 10 confirmations (~12.5 min)
Your vZEC balance is credited on NEXUS

Withdrawal

You request a withdrawal on NEXUS → vZEC burned immediately
Withdrawal queued for batch processing
Protocol signs and broadcasts the Zcash L1 transaction
You receive ZEC in your Zcash wallet

Smart Contract Call

You submit a signed transaction (optionally encrypted via stealth/mempool)
Transaction waits in mempool
Block producer includes it in the next NEXUS block
WASM VM executes the contract function
State changes recorded; events emitted
At next epoch: Groth16 proof generated, state root committed to Zcash L1

Node Architecture

┌─────────────────────────────────────────────────────────────────┐
│                       NEXUS Node                                 │
├─────────────────────────────────────────────────────────────────┤
│                                                                  │
│  ┌─────────────┐  ┌─────────────┐  ┌─────────────┐              │
│  │    RPC      │  │  Prover     │  │  Relayer    │              │
│  │   Server    │  │  (Groth16)  │  │  (L1 txs)  │              │
│  └─────────────┘  └─────────────┘  └─────────────┘              │
│                                                                  │
│  ┌─────────────┐  ┌─────────────┐  ┌─────────────┐              │
│  │   WASM      │  │   Vault     │  │  Watchtower │              │
│  │   VM        │  │   Manager   │  │  (fraud     │              │
│  │             │  │             │  │   detection)│              │
│  └─────────────┘  └─────────────┘  └─────────────┘              │
│                                                                  │
│  ┌─────────────┐  ┌─────────────┐  ┌─────────────┐              │
│  │   Zcash     │  │   Bitcoin   │  │  Dogecoin   │              │
│  │   Scanner   │  │   Scanner   │  │  Scanner    │              │
│  │   ✅ Live   │  │   🔄 Soon  │  │   🔄 Soon  │              │
│  └─────────────┘  └─────────────┘  └─────────────┘              │
│                                                                  │
│  ┌──────────────────────────────────────────────────────────┐   │
│  │              Storage (RocksDB key-value database)         │   │
│  └──────────────────────────────────────────────────────────┘   │
│                                                                  │
└─────────────────────────────────────────────────────────────────┘

Node Mode	What it does	Who runs it
Primary	Produces NEXUS blocks, runs prover, commits state to Zcash L1	Main operator
Replica	Syncs from primary, serves read requests	Scaling / redundancy
Archive	Full history, never prunes	Block explorers, auditors

V2: Unified Execution Layer

When Bitcoin and Dogecoin join, NEXUS becomes a single execution layer across all three chains. V2 adds intent exchange — swap across chains without manually managing deposits and withdrawals:

You declare: "Swap 1 ZEC for at least 50,000 DOGE"
                    ↓
Solver network sees your intent and competes to fill it
                    ↓
Best solver executes across chains atomically
                    ↓
You receive DOGE; solver earns a small fee

No price slippage surprise. No counterparty risk. MEV protection built in.

Getting Started

Supported Chains

Core Concepts

Smart Contracts

Guides

Reference

What is NEXUS?

V1 vs V2 — What’s Available Now

Core Components

Execution Layer

WASM Virtual Machine (Smart Contract Engine)

State Processor

Encrypted Mempool

Fee Market (EIP-1559 Style)

Bridge Layer

Zcash Bridge ✅ Live

Bitcoin Bridge 🔄 Coming soon

Dogecoin Bridge 🔄 Coming soon

Security Layer

How NEXUS Ensures Correctness

Verification by Chain

Vault Architecture

Escape Hatch Waiting Periods

Privacy Layer

Transaction Flow (on Zcash)

Deposit

Withdrawal

Smart Contract Call

Node Architecture

V2: Unified Execution Layer

​What is NEXUS?

​V1 vs V2 — What’s Available Now

​Core Components

​Execution Layer

​WASM Virtual Machine (Smart Contract Engine)

​State Processor

​Encrypted Mempool

​Fee Market (EIP-1559 Style)

​Bridge Layer

​Zcash Bridge ✅ Live

​Bitcoin Bridge 🔄 Coming soon

​Dogecoin Bridge 🔄 Coming soon

​Security Layer

​How NEXUS Ensures Correctness

​Verification by Chain

​Vault Architecture

​Escape Hatch Waiting Periods

​Privacy Layer

​Transaction Flow (on Zcash)

​Deposit

​Withdrawal

​Smart Contract Call

​Node Architecture

​V2: Unified Execution Layer

What is NEXUS?

V1 vs V2 — What’s Available Now

Core Components

Execution Layer

WASM Virtual Machine (Smart Contract Engine)

State Processor

Encrypted Mempool

Fee Market (EIP-1559 Style)

Bridge Layer

Zcash Bridge ✅ Live

Bitcoin Bridge 🔄 Coming soon

Dogecoin Bridge 🔄 Coming soon

Security Layer

How NEXUS Ensures Correctness

Verification by Chain

Vault Architecture

Escape Hatch Waiting Periods

Privacy Layer

Transaction Flow (on Zcash)

Deposit

Withdrawal

Smart Contract Call

Node Architecture

V2: Unified Execution Layer