[Security] Formal Invariant Property Testing & Fuzzing Harness for Economic Solvency

[blurbeast]

Overview & Background

Smart contracts escrowing user assets must satisfy strict mathematical invariants regardless of sequence ordering, arbitrary timestamps, rate modifications, or extreme token amounts. While standard unit tests cover nominal paths, edge-case rounding errors or balance accounting bugs can lead to protocol insolvency (where the contract's actual token balance is less than the cumulative claimable debt owed to stream recipients).

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Detailed Problem Statement

1. Complex Interleaved State Machine:
   • Complex lifecycle permutations (e.g. create -> pause -> top_up -> cliff_pass -> partial_withdraw -> resume -> cancel) may introduce rounding drift or state inconsistencies.
2. Integer Truncation & Stroop Precision:
   • Integer division in rate_per_second accrual calculations can accumulate 1-stroop discrepancies over millions of seconds.

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Technical Specification & Architecture

1. Invariants to Mathematically Prove

Implement in contracts/stream_contract/src/property_tests.rs:

• Contract Solvency Invariant:
  $$\text{Contract Balance} \ge \sum_{i \in \text{ActiveStreams}} (\text{Deposited}_i - \text{Withdrawn}_i)$$
• Zero-Sum Completion Invariant:
  When a stream completes, $\text{Deposited} == \text{Withdrawn}$, with zero stranded dust remaining.
• Monotonic Claimability Invariant:
  For any stream without top-up, $\text{Claimable}(t_2) \ge \text{Claimable}(t_1)$ for all $t_2 \ge t_1$.
• Cliff Protection Invariant:
  For all ledger timestamps $t < \text{cliff_time}$, $\text{Claimable}(t) \equiv 0$.

2. Stateful Fuzzing Runner (proptest)

• Executes 20,000 generated sequences with randomized action selections, amounts up to $10^{18}$, rates, and ledger timestamp increments.
• Asserts all four invariants after every single state mutation.

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Target Files

• contracts/stream_contract/src/property_tests.rs
• contracts/stream_contract/Cargo.toml

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Acceptance Criteria

• Property test suite executes 20,000 iterations without panicking or violating invariants.
• Catches potential integer overflow or negative claimable amounts under adversarial inputs.
• Added to continuous integration pipeline (cargo test).

[pimaster900]

@pimaster900 has applied to work on this issue as part of the Stellar Wave Program's 9th wave.

i would like to work on this

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[Cyb3rflex]

@Cyb3rflex has applied to work on this issue as part of the Stellar Wave Program's 9th wave.

I’d like to work on this issue because it combines smart contract testing, property-based testing, and security-focused invariant validation. I have experience with cybersecurity, backend development, testing, and identifying edge cases in software systems. I can implement the invariant checks in property_tests.rs, build the stateful fuzzing strategy with proptest, cover randomized lifecycle sequences and extreme values, and verify the invariants after each state transition. I’ll also integrate the property tests into the existing Cargo test workflow and ensure the suite remains reliable in CI.

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[ajetunmobiabdulsamad]

@ajetunmobiabdulsamad has applied to work on this issue as part of the Stellar Wave Program's 9th wave.

Hello! I’m very keen to take on this task and would appreciate the assignment. Thanks!

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[boluxx123]

@boluxx123 has applied to work on this issue as part of the Stellar Wave Program's 9th wave.

Please assign

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[Mikardo001]

@Mikardo001 has applied to work on this issue as part of the Stellar Wave Program's 9th wave.

Hey, please assign, i can fix this very fast

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