InterLink

Overview

InterLink is a zero-knowledge interoperability protocol enabling mathematically guaranteed cross-chain state transitions. By utilizing zk-SNARKs (Halo2 with Groth16 on BN254) and a high-throughput Solana Coordination Hub, InterLink enables instant, permissionless cross-chain message passing and asset transfers with O(1) on-chain verification.

The protocol follows a Hub-and-Spoke architecture where Solana acts as the central settlement and verification layer, while EVM chains (Ethereum, Optimism, Arbitrum, Base, Polygon), Cosmos IBC chains, and future networks serve as spoke gateways.

IMPORTANT – PROVER CONSISTENCY REQUIREMENT

The relayer's Halo2 prover MUST use the exact same interlink_v1_domain salt when generating proofs. This is strictly required to match the updated Solidity input binding logic in InterlinkGateway.sol:L175-180. Ensure the entire pipeline (prover -> relayer -> on-chain verification) uses consistent domain separation to prevent proof mismatches.

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Why InterLink?

Feature	Wormhole	Stargate	Across	LiFi	InterLink
Verification	Guardian multisig (19)	UltraLight Client	Optimistic Oracle	Aggregated	ZK proofs (O(1))
Settlement	2-15 min	1-2 min	5-60 min	Varies	<30 seconds
Fees (Tier 1)	$1-20 VAA	$0.50-5	0.25-1%	Varies	0% (zero-fee)
Proof model	Trust 13/19 guardians	Trust relayer	Trust 5 signers	Trust bridge	Trustless math
Uptime SLA	99.95% (informal)	None published	None	None	99.9% (enforced)
Governance	Guardian multisig	Snapshot (off-chain)	UMA Oracle	None	On-chain DAO
Audit trail	On-chain VAA log	None	None	None	SHA-256 hash-chain
Rate limiting	None	None	None	50 req/min	100 req/min free
Bug bounty	$50k-2M	Varies	Varies	None	$100-500k
LP incentives	None	STG emissions	ACX rewards	None	Epoch-based + boost

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Project Architecture

interlink/
├── circuits/                    # ZK circuit definitions
│   ├── src/
│   │   ├── merkle.rs           # Poseidon Merkle inclusion proofs
│   │   ├── consensus.rs        # Ethereum Sync Committee + Tendermint circuits
│   │   ├── folding.rs          # Recursive proof folding pipeline
│   │   └── config.rs           # Circuit configuration
│   └── Cargo.toml
├── contracts/
│   ├── evm/
│   │   ├── src/InterlinkGateway.sol    # EVM spoke gateway (Solidity 0.8.28)
│   │   ├── script/Deploy.s.sol         # Mainnet deployment
│   │   ├── script/DeployL2.s.sol       # L2 deployment (OP/Arb/Base/Polygon)
│   │   └── test/InterlinkGateway.t.sol # Foundry fuzz tests (23 tests)
│   ├── solana/interlink-hub/
│   │   ├── programs/interlink-hub/     # Anchor program (BN254 pairing)
│   │   └── tests/                      # Devnet integration tests
│   └── cosmos/interlink-gateway/       # CosmWasm gateway (IBC-ready)
├── relayer/
│   ├── src/
│   │   ├── main.rs             # Entry point, env config, task spawning
│   │   ├── lib.rs              # Module registry (33 modules)
│   │   └── [33 modules]       # See Module Reference below
│   ├── tests/
│   │   ├── security.rs         # 30 security-focused tests
│   │   └── integration.rs      # 18 end-to-end integration tests
│   └── bin/
│       ├── benchmark.rs        # Proof generation benchmarks
│       └── load_test.rs        # Concurrent transfer load testing
├── interlink-core/             # Core circuit engine + payload types
├── sdk/                        # @interlink/sdk TypeScript package
└── website/                    # Developer portal (React + Vite)

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Relayer Module Reference (33 modules)

The relayer is the heart of InterLink — a standalone Rust service with 33 specialized modules organized by domain.

Core Bridge Pipeline

Module	File	Description
listener	listener.rs	WebSocket EVM event subscription with exponential backoff reconnection. Parses MessagePublished, SwapInitiated, NFTLocked events from gateway contracts.
events	events.rs	GatewayEvent enum with typed variants for Deposit, Swap, and NFTLock. ABI-compatible decoding from EVM log topics + data.
finality	finality.rs	Per-chain finality confirmation. Polls EVM HTTP RPC for block confirmations. Supports configurable confirmation counts per chain (Ethereum: 75 blocks, L2s: 1-2 blocks).
prover	prover.rs	Halo2 Groth16 proof generation on BN254. Domain-separated with interlink_v1_domain salt. Semaphore-bounded concurrent proving with spawn_blocking. Result-based error propagation (no panics in async runtime).
submitter	submitter.rs	Builds and submits raw Solana transactions with ZK proofs. Compact-u16 encoding, PDA derivation (state_registry, stake_account, vk), cached keypair loading.
batch	batch.rs	BatchCollector aggregates transfers into single settlement transactions every 5 seconds. Configurable batch size with flush-on-full.
nonce	nonce.rs	DurableNoncePool for parallel Solana settlement (10-100 concurrent nonces). Lock-free acquire/release with exhaustion alerting.

Economics & Fees

Module	File	Description
fee	fee.rs	Dynamic fee tier engine. Zero ($0-1k), Standard 0.05% ($1k-100k), Institutional 0.01% ($100k-10M), OTC 0% ($10M+). Beats Wormhole VAA fees and Across 0.25-1%.
gas	gas.rs	Cross-chain gas cost estimation with amortized proof generation overhead. CostComparison benchmarks against Wormhole/Stargate/Across fee models.
mev	mev.rs	MEV capture revenue modeling. Computes LP breakeven analysis — minimum daily volume for zero-fee Tier 1 sustainability.
amm	amm.rs	Constant-product AMM (x*y=k) for bridge vault liquidity. LP fee split: 0.25% to LPs + 0.05% protocol. 5% max price-impact guard. APY tracking with real-time yield computation.

Governance & Token Economics

Module	File	Description
governance	governance.rs	DAO governance: 1B $INTERLINK supply (40% community, 30% team, 30% treasury). Proposal creation (100k threshold), 7-day voting, 2-day timelock, treasury disbursement. 6 proposal types: UpdateFees, AddChain, UpdateValidatorSet, TreasuryAllocation, UpdateParameters, Text.
staking	staking.rs	$INTERLINK staking with Bronze/Silver/Gold/Platinum tiers (1k-1M token thresholds). 10-100% fee discounts, 20%→5% APY taper, validator eligibility, configurable slashing (5% downtime, 50% byzantine).
validator_rewards	validator_rewards.rs	10% bridge fee distribution to validators, weighted by stake × uptime. Minimum 90% uptime requirement. 5% bonus for perfect uptime. Epoch-based heartbeat tracking.
vesting	vesting.rs	Token vesting schedules: team (4yr vest, 1yr cliff), advisors (2yr vest, 6mo cliff), treasury (3yr linear, no cliff). Per-beneficiary tracking with revocation support for departed team members.
liquidity_mining	liquidity_mining.rs	LP incentive program: 10M $INTERLINK over 26 epochs (6 months). Early-bird 2x boost (epochs 1-4), loyalty 1.5x boost (≥4 consecutive epochs), 25/75 immediate/vesting split, 24h anti-gaming minimum deposit.
bounty	bounty.rs	Bug bounty lifecycle: Critical $100k-$500k, High $10k-$100k, Medium $1k-$10k, Low $100-$1k. SLA response times: Critical 4h, High 24h, Medium 72h, Low 168h. Full submission→triage→confirm→pay pipeline.

Security & Resilience

Module	File	Description
multisig	multisig.rs	Threshold multi-signature (3-of-5 Ed25519). Validator bundle creation, signature aggregation, and verification. Upgradeable to 13-of-19 (Wormhole parity) via governance vote.
circuitbreaker	circuitbreaker.rs	Auto-pause on anomaly: ≥5 consecutive proof failures, ≥3 settlement failures, $1M TVL drain in 5min. Guardian emergency pause. Auto-recovery after 5min cooldown (non-guardian pauses only).
retry	retry.rs	Exponential backoff with jitter, per-chain retry policies (Ethereum: 2s base/8 retries, Solana: 200ms/4 retries, L2: 500ms/5 retries). Circuit-breaker-aware. Dead-letter queue (1k capacity) for manual replay of failed ops.
ratelimit	ratelimit.rs	Token-bucket rate limiting: Free 100 req/min, Pro 1000 req/min, Enterprise custom/unlimited. 2x burst allowance. Standard X-RateLimit-* response headers.

Routing & Simulation

Module	File	Description
intent	intent.rs	Intent-based routing: user specifies desired output ("1 ETH → ≥2900 USDC on Solana"), solver finds optimal path. Route types: DirectBridge, BridgeAndSwap, MultiHop, SameChainSwap. 2% max slippage, 3-hop max, 5-min expiry.
swap_routing	swap_routing.rs	Multi-DEX aggregation: Uniswap V3, 1inch, 0x, SushiSwap, Curve (EVM) and Jupiter, Raydium, Orca (Solana). Best-rate selection with fallback routing, slippage tracking, and per-source reliability analytics.
simulator	simulator.rs	Transfer dry-run with 10 pre-flight checks: circuit breaker, source/dest chain support, cross-chain validation, amount, fee calculation, liquidity, rate limit, estimated time, route type. No on-chain submission.
wrapped	wrapped.rs	Canonical wrapped asset registry: wETH, wSOL, wMATIC across 6 chains (Ethereum, Optimism, Polygon, Arbitrum, Base, Solana). Deterministic resolve-or-no-wrap — no manual attestation step.

NFT & Atomic Settlement

Module	File	Description
nft_bridge	nft_bridge.rs	Cross-chain NFT bridging with lock-mint-burn model. Full metadata preservation (name, traits, IPFS/Arweave URIs, on-chain SVG). EIP-2981 royalty forwarding. Wrapped contract registry. 24h lock timeout with auto-expiry.
atomic	atomic.rs	Two-phase commit for cross-chain settlement. Escrow state machine: Prepared → ProofReady → Committed → Finalized, with timeout-based rollback. Grace period before forced rollback. Guarantees: no fund loss, no double-spend.

Enterprise Features

Module	File	Description
enterprise	enterprise.rs	Institutional bridge controls: address whitelisting, per-tx/daily/monthly spend limits ($500k/$1M/$10M defaults), N-of-M multi-approver workflows for large transfers ($100k+), configurable settlement hold period, auto-resetting spend counters.

Observability & Compliance

Module	File	Description
metrics	metrics.rs	Prometheus-compatible metrics: proof gen time (p50/p95/p99), settlement time, verification time (>500ms alert), per-chain finality lag, RPC latency, TVL tracking, daily/cumulative volume, validator uptime %, daily transfers, unique users, top corridors. JSON + Prometheus text export.
sla	sla.rs	SLA monitoring: 99.9% uptime target, <60s settlement p99, <500ms API response p99. Sliding window (10k samples), automatic breach detection and reporting.
audit_trail	audit_trail.rs	Append-only compliance log with SHA-256 hash-chain integrity. Indexed by sender, receiver, corridor, time range. CSV + JSON export for regulatory reporting. Tamper detection via verify_integrity().
webhook	webhook.rs	Real-time push notifications: transfer start, pending, completed, failed. 3-attempt exponential backoff. Auto-disable after 10 consecutive failures.
http_api	http_api.rs	REST API: GET /health, GET /metrics, GET /quote, POST /simulate. Prometheus endpoint for Grafana integration.

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Testing Framework

InterLink employs a multi-layered testing strategy with 451 tests across all layers, all verified passing.

Full Test Suite Summary

Layer	Tool	Tests	Status
Relayer lib (unit)	cargo test --lib	366	All passing
Relayer security	cargo test --test security	30	All passing
Relayer integration	cargo test --test integration	18	All passing
ZK Circuits	cargo test -p circuits	10	All passing
EVM Gateway (Solidity)	forge test	23	All passing
Solana Hub (devnet)	Anchor / Mocha	4	All passing
Total		451	All passing

Security Test Coverage (30 tests)

Module	Tests	What's Validated
sequence_binding	3	Double-spend prevention, commitment binding, replay rejection
byzantine	6	Threshold enforcement (2/5, 3/5), duplicate signer detection, empty bundle rejection
malformed_input	5	Invalid proof data, oversized payloads, zero-amount transfers
amm_manipulation	4	Price impact guard, zero-amount swap rejection, slippage protection
governance_attack	5	Insufficient stake voting, double-vote prevention, premature execution
rate_limit	4	Free tier enforcement, Pro tier scaling, Enterprise unlimited, burst handling
webhook_dos	3	Auto-disable after failures, delivery tracking, registration limits

Running Tests

# All Rust tests (circuits + relayer)
cargo test --workspace

# Relayer unit tests only
cargo test --lib

# Security tests
cargo test --test security

# Integration tests
cargo test --test integration

# EVM Solidity (requires Foundry)
cd contracts/evm && forge test -vv

# Solana devnet (requires SOL balance + Anchor CLI)
cd contracts/solana/interlink-hub
ANCHOR_PROVIDER_URL=https://api.devnet.solana.com \
ANCHOR_WALLET=~/.config/solana/id.json \
yarn run ts-mocha -p ./tsconfig.json -t 1000000 "tests/**/*.ts"

# Performance benchmarks
cargo run --bin benchmark -- --iterations 1000

# Load testing
cargo run --bin load_test -- --concurrency 50 --total 1000

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Specialized Circuits (circuits/)

Advanced ZK primitives built on Halo2 over BN254:

Circuit	Purpose	Details
Merkle Circuit	Poseidon Merkle inclusion proofs	Binary tree traversal with quintic S-box hash gates
SyncCommitteeCircuit	Ethereum beacon chain finality	BLS-aggregate participation accumulation, ≥342/512 quorum threshold
TendermintCircuit	Cosmos Tendermint finality	>2/3 voting power accumulation gate
FoldingCircuit	Recursive proof aggregation	Pairwise folding with Fiat-Shamir challenge alpha = (C1+C2)^5, O(log N) depth
BatchedInterlinkCircuit	Multi-message batching	O(1) on-chain verification for N cross-chain messages in a single SNARK

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Multi-Chain Contracts

EVM Spoke Gateway (contracts/evm/)

Solidity 0.8.28 with BN254 pairing precompiles:

• InterlinkGateway.sol: Message routing, swap initiation, NFT locking, ZK proof verification
• Deploy.s.sol: Mainnet deployment with guardian address configuration
• DeployL2.s.sol: L2-specific deployment (Optimism, Arbitrum, Base, Polygon) with per-chain finality calibration
• 23 Foundry tests including fuzz tests (256 runs each)

Solana Hub Gateway (contracts/solana/interlink-hub/)

Anchor-based program with alt_bn128 syscalls:

• Program ID: AKzpc9tvxfhLjj5AantKizK2YZgSjoyhLmYqRZy6b8Lz
• PDA derivation: state_registry, stake_account, vk accounts
• submit_proof: Verifies ZK proof, mints/releases on destination
• process_cross_chain_swap: AMM integration with stake verification
• Live on Solana devnet with 4 passing integration tests

Cosmos Gateway (contracts/cosmos/)

CosmWasm-based gateway for IBC-connected chains:

• Initial implementation for Tendermint consensus verification
• IBC channel management for cross-chain message relay

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Token Economics

$INTERLINK Token

Parameter	Value
Total Supply	1,000,000,000 (1B)
Community / Mining	400,000,000 (40%)
Team (4yr vest, 1yr cliff)	300,000,000 (30%)
Treasury (DAO-governed)	300,000,000 (30%)

Fee Tiers

Tier	Transfer Size	Fee	vs Wormhole	vs Across
Zero	$0 - $1,000	0%	Wormhole: $1-20 VAA	Across: 0.25-1%
Standard	$1k - $100k	0.05%	Wormhole: 0.1-0.2%	Across: 0.25-1%
Institutional	$100k - $10M	0.01%	Wormhole: negotiated	Across: negotiated
OTC	$10M+	0% (negotiated)	—	—

Staking Tiers

Tier	Min Stake	Fee Discount	Extra Benefits
Bronze	1,000	10%	Basic participation
Silver	10,000	25%	Governance voting
Gold	100,000	50%	Validator eligibility
Platinum	1,000,000	100%	Enhanced APY + zero fees

Liquidity Mining Program

• Budget: 10,000,000 $INTERLINK over 26 weekly epochs (6 months)
• Early-bird boost: 2x rewards in epochs 1-4 to bootstrap liquidity
• Loyalty boost: 1.5x for LPs with ≥4 consecutive epochs
• Vesting: 25% immediate release, 75% linear over 90 days
• Anti-gaming: 24-hour minimum deposit before earning rewards

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Security Model

ZK Proof Verification

Every cross-chain message is verified by a Halo2 Groth16 proof on BN254. The on-chain verifier performs a single pairing check — O(1) regardless of message complexity. Domain separation via keccak256("interlink_v1_domain") prevents cross-protocol proof reuse.

Multi-Layer Protection

Layer	Mechanism	Auto-Trigger
Circuit Breaker	Auto-pause bridge operations	≥5 proof failures, ≥3 settlement failures, $1M outflow in 5min
Guardian Pause	Emergency manual pause	Authorized guardian key hash
Threshold Multi-Sig	3-of-5 Ed25519 validator co-signing	All settlement transactions
Rate Limiting	Token-bucket per API key	Free: 100/min, Pro: 1000/min
Retry Engine	Exponential backoff with dead-letter queue	Per-chain optimized policies
Audit Trail	SHA-256 hash-chain append-only log	Every transfer recorded

Validator Economics

• 10% fee share distributed to validators per epoch
• Weighted by: stake amount × uptime percentage
• Minimum uptime: 90% required for reward eligibility
• Perfect uptime bonus: +5% additional rewards
• Slashing: 5% for downtime, 50% for byzantine behavior

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Technical Specifications

Parameter	Value
Proving System	Halo2 (IPA commitment, BN254 scalar field)
Elliptic Curve	BN254 (alt_bn128)
Hash Function	Poseidon quintic S-box (x^5), injective over BN254
Domain Separation	keccak256("interlink_v1_domain")
Verification Complexity	O(1) on-chain
State Commitment	Sparse Merkle Trees
Recursion	Pairwise folding, O(log N) depth, Fiat-Shamir alpha = (C1+C2)^5
Consensus (ETH)	Sync Committee 342/512 threshold
Consensus (Cosmos)	Tendermint >2/3 voting power
Settlement Target	<30 seconds end-to-end
Uptime SLA	99.9% (8.76h max annual downtime)
Settlement SLA	<60s p99
API Response SLA	<500ms p99

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Developer Setup

Prerequisites

• Rust (Edition 2021)
• Solana CLI (>=1.18) & Anchor CLI (0.32.1)
• Foundry (forge, cast, anvil) — install via foundryup
• Node.js & yarn (for Anchor TypeScript tests and website)

Building the Workspace

# Build all Rust crates
cargo build --release

# Build the Solana Hub program
cd contracts/solana/interlink-hub
anchor build

# Build EVM contracts
cd contracts/evm
forge build

Environment Variables

# Required
EVM_WS_RPC_URL=wss://...          # WebSocket for event subscription
EVM_HTTP_RPC_URL=https://...       # HTTP for finality polling
SOLANA_RPC_URL=https://...         # Solana RPC endpoint
GATEWAY_ADDRESS=0x...              # EVM gateway contract address
HUB_PROGRAM_ID=AKzpc9...          # Solana hub program ID
KEYPAIR_PATH=/path/to/keypair.json # Solana relayer keypair

# Optional
LOG_FORMAT=json                    # Structured JSON logging (default: text)
BATCH_SIZE=50                      # Transfers per batch (default: 50)
NONCE_POOL_SIZE=10                 # Parallel Solana nonces (default: 10)

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Observability

Prometheus Metrics

The relayer exposes a GET /metrics endpoint compatible with Prometheus/Grafana:

# Proof generation
proof_gen_ms_p50, proof_gen_ms_p95, proof_gen_ms_p99
proof_gen_total, proof_gen_alerts

# Settlement
settlement_ms_p50, settlement_ms_p95, settlement_ms_p99
settlement_total, settlement_alerts

# Verification
verify_ms_mean, verify_ms_max, verify_alerts

# Chain health (per-chain)
chain_finality_mean_ms{chain_id="1"}
chain_rpc_latency_ms{chain_id="1"}

# User metrics
daily_transfers, unique_users
corridor_count{corridor="1:900"}

# TVL & Volume
tvl_usd_cents, daily_volume_usd_cents, cumulative_volume_usd_cents

# Validator uptime
validator_heartbeats_total, validator_heartbeats_expected

Alerting Thresholds

Metric	Alert Threshold	Action
Proof gen time	>1 second	Investigate prover load
Verification time	>500ms	Check verifier efficiency
Settlement finality	>60 seconds	Check chain congestion
Validator downtime	>15 minutes	Check nonce pool exhaustion
Circuit breaker	Any auto-pause	Incident response playbook

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Solana Hub — Live Devnet Deployment

• Program ID: AKzpc9tvxfhLjj5AantKizK2YZgSjoyhLmYqRZy6b8Lz
• Deploy Transaction: 59bSsMZU9GZAvaVL5mEL8NQ24Ucs4HvgpQ7i9TmnFDYPdANivm24n3b18Yb5Nx2aSZYp9ti3NmT7GF1jsd2v59ZY
• IDL Account: 3YddvfRCPY6MALVoVzAN59njDkzCEQ3px2NMhszBrZpp
• Cluster: Solana Devnet

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Documentation and Resources

• Technical Whitepaper: InterLink Research (PDF)
• Developer Portal: interlink.protocol
• GitHub Repository: MeridianAlgo/Interlink