invariant-analysis

Search for require and assert statements plus NatSpec @invariant annotations to find explicit invariants, then analyze state variable modification and read patterns to infer implicit ones. The framework maps variables like totalSupply to their setter and getter functions to derive relationships.

A first depositor attack occurs when an attacker deposits a minimal amount, donates assets directly to inflate totalAssets, and causes subsequent depositors to receive zero shares due to rounding. It violates the invariant that totalAssets and totalShares maintain a fair exchange ratio.

Common invariants include balance invariants (totalSupply equals sum of balances), accounting invariants (totalBorrowed within utilization caps), AMM invariants (reserveX times reserveY at least k), and bridge invariants (minted on L2 equals locked on L1).

Analyze code flow patterns such as share calculations, balance subtractions, and reward distributions to infer conditions the code assumes. For example, a subtraction like balance[from] minus amount implicitly requires the balance to be sufficient.

Run invariant analysis after code reconnaissance and documentation review, during the deep logic auditing phase. It works best once you understand the protocol's state variables, fund flows, and documented design assumptions.