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designing-assertions

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Designs Phylax Credible Layer assertion invariants and trigger mapping. Use when scoping protocols, selecting invariants, or mapping functions to checks.

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Designing Assertions

Design high-signal invariants and map them to precise triggers before writing any Solidity.

When to Use

  • Starting a new assertion suite for a protocol or contract.
  • Turning protocol rules into enforceable pre/post invariants.
  • Choosing between call, storage, or balance triggers.

When NOT to Use

  • You need to discover invariants from scratch. Use mapping-invariants.
  • You only need cheatcode syntax or implementation details. Use implementing-assertions.
  • You only need test harness patterns. Use testing-assertions.
  • You are doing a general security review without writing assertions.

Quick Start

  1. Identify assets, roles, and trust boundaries.
  2. List state transitions that can violate safety properties.
  3. Express invariants as pre/post comparisons or event-accounting rules.
  4. Select data sources (state, logs, call inputs, storage slots).
  5. Choose minimal triggers that cover all violating paths.

Workflow

  • Build a protocol map: key contracts, roles, assets, mutable state.
  • Draft invariants in plain language and math form.
  • Identify legitimate exceptions in specs/audits and encode them explicitly.
  • Decide if the invariant is transaction-scoped (pre/post) or call-scoped (per call id).
  • Choose enforcement location (per-contract vs chokepoint) based on call routing.
  • Flag upgradeability/proxy entrypoints and token integration assumptions.
  • Pick observation strategy:
    • State comparisons for monotonicity and conservation.
    • Event-based accounting when internal state is opaque.
    • Call input parsing for authorization or parameter bounds.
  • Map to triggers with the smallest blast radius.
  • Enumerate edge cases (zero supply, empty vaults, proxy upgrades, nested batches).

Rationalizations to Reject

  • "Trigger on any call; it is simpler." This risks gas-limit reverts and false drops.
  • "Post-state is enough." Many invariants need pre/post deltas.
  • "Ignore batch or nested calls." Real protocols use them heavily.
  • "We can skip edge cases like zero supply." These are common sources of false positives.

Deliverable

  • Invariant spec with: definition, data sources, trigger list, and edge cases.
  • A candidate list of assertion functions with one invariant per function.

References