Moistello Smart Contracts

Rust/Soroban smart contracts implementing ROSCA (Rotating Savings and Credit Association) protocol for 1.7B+ unbanked adults on Stellar.

Business Model

Smart contracts hold circle funds in escrow, enforce contribution rules, distribute payouts automatically, and maintain on-chain MoiScore reputation. No central party controls funds.

Contract Architecture (5 Contracts)

contracts/
├── circle-factory/         # Deploys new Circle instances, maintains registry
├── circle/                 # Core ROSCA engine (per-circle contract)
├── reputation-registry/    # On-chain MoiScore calculation/storage
└── treasury/               # Collects 0.5% protocol fee

Revenue Collection

Treasury contract collects 0.5% fee on every payout distribution. Fee split across platform sustainability and future DAO treasury.

Circle Contract (Core Engine)

State Machine

[Created] → [Funding] → [Active] → [Completed]
     ↓          ↓           ↓
  Cancelled   Defaulted    Paused

ROSCA Parameters

Parameter	Description	Configurable
Contribution Amount	USDC/XLM per cycle	Yes
Currency	USDC or XLM	Yes
Frequency	Daily/Weekly/Biweekly/Monthly	Yes
Max Members	Circle capacity	Yes
Late Fee	Penalty percentage	Yes (default 5%)
Grace Period	Hours before late	Yes (1-168h, default 24h)
Max Strikes	Removal threshold	Yes (1-10, default 3)
Payout Type	Random/Fixed/Auction/Vote	Yes

Payout Types

Type	Function	Algorithm
Random	payout_random()	VRF selection, provably fair
Fixed	payout_fixed()	Sequential by member index
Auction	payout_auction()	Lowest discount bidder wins
Merit	payout_merit()	Reputation-weighted selection

Member Lifecycle

Status	Trigger
pending	Joined, awaiting quorum
active	Circle started, in rounds
late	Missed grace period
removed	Exceeded max strikes

Events

emit_member_joined(member: Address, deposit: u128);
emit_contribution_submitted(member: Address, amount: u128);
emit_payout_processed(payout_type: PayoutType, winner: Address);
emit_penalty_applied(member: Address, amount: u128);

Reputation Registry Contract

MoiScore Formula (0-1000)

MoiScore = Streak×0.35 + Completions×0.30 + Volume×0.20 + Recency×0.15

Score Tiers

Range	Tier	Benefits
0-200	Bronze	Basic access
201-400	Silver	Higher limits
401-600	Gold	Premium access
601-800	Platinum	Governance voting
801-1000	Diamond	Zero collateral

Functions

• calculate_score(address: Address): Compute current MoiScore
• record_contribution(address, amount, cycle): Add to user score
• get_score(address): Retrieve stored MoiScore

Treasury Contract

Functions

• collect_fee(amount, circle_id): Take 0.5% fee
• withdraw(amount): Admin withdrawal
• get_balance(): Current treasury holdings

Security Architecture

Access Control

enum Role {
    Admin,
    Organizer,
    Member,
}

Safe Math

All arithmetic uses checked operations to prevent overflow/underflow.

Security Features

Feature	Implementation
Authorization	Address-based caller verification
Pause Mechanism	Emergency stop via Admin
Input Validation	Contract-level checks
Integer Safety	Checked arithmetic
Reentrancy	Sequential execution model
No unwrap()	Panic-safe operations

Development

Prerequisites

• Rust 1.70+
• Soroban CLI 21.x
• Stellar account with test XLM

Build Commands

Command	Purpose
cargo build	Compile WASM
cargo test	Run 45 unit tests
make optimize	Optimize for deployment
make deploy-testnet	Deploy to testnet
make deploy-mainnet	Deploy to mainnet
make bindings	Generate Go bindings

Gas Optimization

All contracts under 50KB WASM target size. Optimized for minimal on-chain storage and batch operations.

Deployment

Testnet

soroban config identity --secret <secret-key>
make deploy-testnet

Mainnet

make deploy-mainnet
sha256sum target/wasm32v1-none/release/circle.wasm

Network Endpoints

Network	RPC URL
Testnet	https://soroban-testnet.stellar.org
Mainnet	https://soroban-mainnet.stellar.org

Integration

Go bindings generated via make bindings:

type Client struct {
    contractID string
    signer     keypair.KP
}

func (c *Client) Initialize(params InitializeParams) error
func (c *Client) Join(member string, amount int64) error
func (c *Client) Contribute(member string, amount int64) error

Testing Matrix

Test Type	Coverage	Tests
Unit	92%	45 tests
Property	85%	12 tests
Integration	78%	8 tests
Fuzz	65%	3 tests

License

Apache 2.0