Running the certora verification tool

These instructions detail the process for running Certora Verification Tool on OpenZeppelin Contracts.

Documentation for CVT and the specification language are available here.

Prerequisites

Follow the Certora installation guide in order to get the Certora Prover Package and the solc executable folder in your path.

Note An API Key is required for local testing. Although the prover will run on a Github Actions' CI environment on selected Pull Requests.

Running the verification

The Certora Verification Tool proves specs for contracts, which are defined by the ./specs.json file along with their pre-configured options.

The verification script ./run.js is used to submit verification jobs to the Certora Verification service.

You can run it from the root of the repository with the following command:

node certora/run.js [[CONTRACT_NAME:]SPEC_NAME] [OPTIONS...]

Where:

• CONTRACT_NAME matches the contract key in the ./spec.json file and may be empty. It will run all matching contracts if not provided.
• SPEC_NAME refers to a spec key from the ./specs.json file. It will run every spec if not provided.
• OPTIONS extend the Certora Prover CLI options and will respect the preconfigured options in the specs.json file.

Note A single spec may be configured to run for multiple contracts, whereas a single contract may run multiple specs.

Example usage:

node certora/run.js AccessControl # Run the AccessControl spec against every contract implementing it

Adapting to changes in the contracts

Some of our rules require the code to be simplified in various ways. Our primary tool for performing these simplifications is to run verification on a contract that extends the original contracts and overrides some of the methods. These "harness" contracts can be found in the certora/harness directory.

This pattern does require some modifications to the original code: some methods need to be made virtual or public, for example. These changes are handled by applying a patch to the code before verification by running:

make -C certora apply

Before running the certora/run.js script, it's required to apply the corresponding patches to the contracts directory, placing the output in the certora/patched directory. Then, the contracts are verified by running the verification for the certora/patched directory.

If the original contracts change, it is possible to create a conflict with the patch. In this case, the verify scripts will report an error message and output rejected changes in the patched directory. After merging the changes, run make record in the certora directory; this will regenerate the patch file, which can then be checked into git.

For more information about the make scripts available, run:

make -C certora help