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Nestera Smart Contracts: Off-Chain Oracle Architecture

This directory contains the Soroban smart contracts for Nestera, implementing a cost-efficient "Off-Chain Oracle" architecture. This allows users to pay for gas fees while ensuring all minting requests are cryptographically authorized by the Admin.

How it Works

  1. Admin Authorization: The Admin generates a cryptographic signature for a MintPayload off-chain using their Ed25519 private key.
  2. User Submission: The user receives the payload and signature and submits them to the mint function on-chain.
  3. On-Chain Verification: The contract verifies the signature against the stored Admin public key before allowing the minting process to proceed.

Admin: Signing Payloads Off-Chain

The Admin must sign the MintPayload using an Ed25519 private key. The payload must be serialized to XDR format to ensure consistency with the on-chain verification.

Example (Rust)

Using the ed25519-dalek library:

use ed25519_dalek::{Signer, SigningKey};
use soroban_sdk::xdr::ToXdr;

// 1. Create the payload
let payload = MintPayload {
    user: user_address,
    amount: 100,
    timestamp: current_time,
    expiry_duration: 3600,
};

// 2. Serialize to XDR
let payload_bytes = payload.to_xdr(&env);

// 3. Sign with Admin private key
let signature = signing_key.sign(&payload_bytes);

User: Submitting Minting Requests

Users call the mint function themselves, providing the authorized payload and the signature.

Example (Stellar CLI)

stellar contract invoke \
  --id <CONTRACT_ID> \
  --source <USER_IDENTITY> \
  --network testnet \
  -- mint \
  --payload '{ "user": "...", "amount": 100, "timestamp": 1737511200, "expiry_duration": 3600 }' \
  --signature <64_BYTE_HEX_SIGNATURE>

Security & Validation

  • Signature Verification: The contract uses env.crypto().ed25519_verify() to ensure the signature is valid.
  • Expiry Protection: Each payload includes a timestamp and expiry_duration. The contract panics if the current ledger time exceeds the expiry.
  • Tamper Resistance: Any change to the payload (e.g., increasing the amount) will result in an invalid signature and a contract panic.

Development

Building

cargo build --target wasm32-unknown-unknown --release

Testing

cargo test