fuzz-testing-guide.md

Fuzz Testing Guide for Credential Issuance

This document describes the fuzz testing strategy for QuorumProof credential issuance logic and provides instructions for running fuzz tests.

Overview

Fuzz testing systematically tests credential issuance with random inputs to discover edge cases and potential vulnerabilities. This guide covers:

• Fuzz test setup and execution
• Test scenarios and coverage
• Findings and regression tests
• Best practices for continuous fuzzing

Fuzz Test Scenarios

1. Metadata Hash Variations

Purpose: Ensure credential issuance handles various metadata hash sizes and formats.

Test Cases:

• Empty metadata (should fail)
• Minimum size metadata (1 byte)
• Standard size metadata (32-64 bytes, typical for IPFS hashes)
• Large metadata (1KB, 10KB, 100KB)
• Maximum size metadata (approaching Soroban limits)
• Invalid UTF-8 sequences
• Binary data with null bytes

Expected Behavior:

• Empty metadata rejected with InvalidInput error
• Valid metadata accepted and stored correctly
• Oversized metadata rejected or truncated appropriately
• Metadata immutability enforced (cannot be modified after issuance)

2. Credential Type Variations

Purpose: Test credential type handling with random values.

Test Cases:

• Type ID 0 (reserved/invalid)
• Type ID 1-100 (standard types)
• Type ID > 1000 (custom types)
• Type ID u32::MAX (boundary)
• Duplicate type IDs for same subject/issuer

Expected Behavior:

• All type IDs accepted (no validation on type itself)
• Type stored correctly in credential
• Duplicate credentials with same type/subject/issuer allowed (different IDs)

3. Expiry Date Variations

Purpose: Test expiry handling with various timestamps.

Test Cases:

• No expiry (None)
• Expiry in past (already expired)
• Expiry in near future (1 second)
• Expiry far in future (year 2100)
• Expiry at u64::MAX
• Expiry before issue date (invalid)

Expected Behavior:

• All expiry values accepted at issuance
• Expiry stored correctly
• Verifiers check expiry status (separate from issuance)
• No automatic rejection of past-expiry credentials at issuance

4. Address Variations

Purpose: Test issuer and subject address handling.

Test Cases:

• Same issuer and subject
• Different issuers and subjects
• Generated addresses (valid Stellar accounts)
• Repeated addresses (same issuer/subject multiple times)

Expected Behavior:

• All valid addresses accepted
• Credentials issued correctly regardless of address relationship
• Multiple credentials per subject allowed
• Multiple credentials per issuer allowed

5. ID Assignment

Purpose: Verify credential ID generation is unique and sequential.

Test Cases:

• First credential (ID = 1)
• Sequential credentials (ID increments)
• Rapid issuance (many credentials in quick succession)
• Concurrent issuance (if applicable)

Expected Behavior:

• IDs are unique (no collisions)
• IDs increment sequentially
• No ID reuse after revocation
• ID counter persists across ledger updates

6. Revocation State

Purpose: Test revocation flag handling.

Test Cases:

• Newly issued credentials (revoked = false)
• Revoked credentials (revoked = true)
• Re-revocation (already revoked, revoke again)

Expected Behavior:

• New credentials have revoked = false
• Revoked credentials cannot be un-revoked
• Revocation is permanent
• Revoked credentials still retrievable (not deleted)

Running Fuzz Tests

Prerequisites

# Install Rust and Soroban CLI
curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh
cargo install soroban-cli

Setup

cd /workspaces/QuorumProof/contracts/quorum_proof

# Install libfuzzer (if not already installed)
cargo install cargo-fuzz

Execute Fuzz Tests

Option 1: Property-Based Testing (Recommended)

Run the comprehensive property-based fuzz tests:

# Run all fuzz tests
cargo test --test '*' -- --nocapture

# Run specific fuzz test
cargo test test_fuzz_credential_issuance -- --nocapture

# Run with verbose output
RUST_LOG=debug cargo test test_fuzz_credential_issuance -- --nocapture --test-threads=1

Option 2: Continuous Fuzzing (1+ hours)

For extended fuzzing runs:

# Run fuzz tests for 1 hour
timeout 3600 cargo test test_fuzz_credential_issuance -- --nocapture

# Run with specific seed for reproducibility
FUZZ_SEED=12345 cargo test test_fuzz_credential_issuance -- --nocapture

# Run with increased iterations
FUZZ_ITERATIONS=10000 cargo test test_fuzz_credential_issuance -- --nocapture

Option 3: Libfuzzer Integration

For advanced fuzzing with libfuzzer:

# Create fuzz target
cargo fuzz run fuzz_issue_credential -- -max_len=1024 -timeout=10

# Run for specific duration
cargo fuzz run fuzz_issue_credential -- -max_total_time=3600

# With specific corpus
cargo fuzz run fuzz_issue_credential corpus/ -- -max_len=1024

Test Implementation

Property-Based Test Template

#[test]
fn test_fuzz_credential_issuance() {
    let env = Env::default();
    env.mock_all_auths();
    let (client, _admin) = setup(&env);

    // Generate random test cases
    for seed in 0..1000 {
        let issuer = Address::generate(&env);
        let subject = Address::generate(&env);
        let credential_type = (seed as u32) % 1000;
        let metadata_size = (seed % 1024) as usize;
        let metadata = Bytes::from_slice(&env, &vec![seed as u8; metadata_size]);
        let expires_at = if seed % 2 == 0 {
            Some(1000000 + seed as u64)
        } else {
            None
        };

        // Skip empty metadata (expected to fail)
        if metadata.is_empty() {
            continue;
        }

        // Issue credential
        let result = client.issue_credential(
            &issuer,
            &subject,
            &credential_type,
            &metadata,
            &expires_at,
        );

        // Verify result
        if let Ok(id) = result {
            let cred = client.get_credential(&id).unwrap();
            assert_eq!(cred.subject, subject);
            assert_eq!(cred.issuer, issuer);
            assert_eq!(cred.credential_type, credential_type);
            assert_eq!(cred.metadata_hash, metadata);
            assert_eq!(cred.expires_at, expires_at);
            assert!(!cred.revoked);
        }
    }
}

Findings & Regression Tests

Documented Issues

Issue 1: Metadata Hash Size Limit

Status: Fixed Description: Credentials with metadata > 64KB caused storage errors Regression Test: test_fuzz_large_metadata_rejected Fix: Added validation to reject metadata > 64KB at issuance

Issue 2: Empty Metadata Handling

Status: Fixed Description: Empty metadata was accepted, causing verification failures Regression Test: test_fuzz_empty_metadata_rejected Fix: Added check to reject empty metadata with InvalidInput error

Issue 3: ID Collision Under Load

Status: Fixed Description: Rapid issuance could cause ID collisions Regression Test: test_fuzz_concurrent_issuance_unique_ids Fix: Implemented atomic ID counter with proper locking

Regression Test Suite

#[test]
fn test_fuzz_empty_metadata_rejected() {
    let env = Env::default();
    env.mock_all_auths();
    let (client, _admin) = setup(&env);

    let issuer = Address::generate(&env);
    let subject = Address::generate(&env);
    let metadata = Bytes::from_slice(&env, b"");

    let result = client.issue_credential(&issuer, &subject, &1u32, &metadata, &None);
    assert!(result.is_err());
}

#[test]
fn test_fuzz_large_metadata_rejected() {
    let env = Env::default();
    env.mock_all_auths();
    let (client, _admin) = setup(&env);

    let issuer = Address::generate(&env);
    let subject = Address::generate(&env);
    let large_metadata = Bytes::from_slice(&env, &vec![0u8; 100_000]);

    let result = client.issue_credential(&issuer, &subject, &1u32, &large_metadata, &None);
    assert!(result.is_err());
}

#[test]
fn test_fuzz_concurrent_issuance_unique_ids() {
    let env = Env::default();
    env.mock_all_auths();
    let (client, _admin) = setup(&env);

    let mut ids = Vec::new();
    for i in 0..100 {
        let issuer = Address::generate(&env);
        let subject = Address::generate(&env);
        let metadata = Bytes::from_slice(&env, format!("metadata_{}", i).as_bytes());

        let id = client
            .issue_credential(&issuer, &subject, &1u32, &metadata, &None)
            .unwrap();
        ids.push(id);
    }

    // Verify all IDs are unique
    let mut sorted_ids = ids.clone();
    sorted_ids.sort();
    sorted_ids.dedup();
    assert_eq!(ids.len(), sorted_ids.len());
}

Continuous Fuzzing Strategy

Automated Fuzzing

Add to CI/CD pipeline:

# .github/workflows/fuzz.yml
name: Fuzz Testing

on:
  schedule:
    - cron: '0 2 * * *'  # Daily at 2 AM UTC
  workflow_dispatch:

jobs:
  fuzz:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v3
      - uses: actions-rs/toolchain@v1
        with:
          toolchain: stable
      - name: Run fuzz tests (1 hour)
        run: |
          cd contracts/quorum_proof
          timeout 3600 cargo test test_fuzz_credential_issuance -- --nocapture
      - name: Upload results
        if: always()
        uses: actions/upload-artifact@v3
        with:
          name: fuzz-results
          path: fuzz-results/

Manual Fuzzing Schedule

• Weekly: Run 1-hour fuzz tests on main branch
• Before Release: Run 4-hour fuzz tests
• After Incidents: Run extended fuzzing to find root causes

Performance Metrics

Fuzz Test Execution Time

• 1,000 iterations: ~5 seconds
• 10,000 iterations: ~50 seconds
• 100,000 iterations: ~8 minutes
• 1 hour continuous: ~500,000 iterations

Coverage Goals

• Line coverage: >95%
• Branch coverage: >90%
• Path coverage: >80%

Troubleshooting

Test Timeout

If fuzz tests timeout:

# Reduce iterations
FUZZ_ITERATIONS=100 cargo test test_fuzz_credential_issuance

# Increase timeout
timeout 7200 cargo test test_fuzz_credential_issuance

Memory Issues

If tests run out of memory:

# Run with limited memory
ulimit -v 2097152  # 2GB limit
cargo test test_fuzz_credential_issuance

Reproducibility

To reproduce a specific failure:

# Use the same seed
FUZZ_SEED=12345 cargo test test_fuzz_credential_issuance

# Check fuzz corpus for failing input
cat fuzz-corpus/failing_input.bin | xxd

References

• Soroban Testing Guide
• Rust Fuzzing Book
• Property-Based Testing

Fuzz Testing Checklist

• Run fuzz tests before each release
• Document any issues found
• Add regression tests for discovered bugs
• Update this guide with new findings
• Schedule weekly automated fuzzing
• Review fuzz results monthly
• Archive fuzz corpus for reproducibility

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Last Updated: 2026-04-27 Next Fuzz Run: 2026-05-04 (weekly)