In Publishing, we discussed how you can publish your contract to the world. This looks at the flip-side, how can you use someone else's contract (which is the same question as how they will use your contract). Let's go through the various stages.
Before using remote code, you most certainly want to verify it is honest.
The simplest audit of the repo is to simply check that the artifacts in the repo are correct. This involves recompiling the claimed source with the claimed builder and validating that the locally compiled code (hash) matches the code hash that was uploaded. This will verify that the source code is the correct preimage. Which allows one to audit the original (Rust) source code, rather than looking at wasm bytecode.
We have a script to do this automatic verification steps that can
easily be run by many individuals. Please check out
cosmwasm-verify
to see a simple shell script that does all these steps and easily allows you to verify
any uploaded contract.
Once you have done the quick programatic checks, it is good to give at least a quick
look through the code. A glance at examples/schema.rs to make sure it is outputing
all relevant structs from contract.rs, and also ensure src/lib.rs is just the
default wrapper (nothing funny going on there). After this point, we can dive into
the contract code itself. Check the flows for the handle methods, any invariants and
permission checks that should be there, and a reasonable data storage format.
You can dig into the contract as far as you want, but it is important to make sure there are no obvious backdoors at least.
It's not very practical to do a deep code review on every dependency you want to use, which is a big reason for the popularity of code audits in the blockchain world. We trust some experts review in lieu of doing the work ourselves. But wouldn't it be nice to do this in a decentralized manner and peer-review each other's contracts? Bringing in deeper domain knowledge and saving fees.
Luckily, there is an amazing project called crev
that provides A cryptographically verifiable code review system for the cargo (Rust) package manager.
I highly recommend that CosmWasm contract developers get set up with this. At minimum, we can all add a review on a package that programmatically checked out that the json schemas and wasm bytecode do match the code, and publish our claim, so we don't all rely on some central server to say it validated this. As we go on, we can add deeper reviews on standard packages.
If you want to use cargo-crev, please follow their
getting started guide
and once you have made your own proof repository with at least one trust proof,
please make a PR to the cawesome-wasm repo with a link to your repo and
some public name or pseudonym that people know you by. This allows people who trust you
to also reuse your proofs.
There is a standard list of proof repos
with some strong rust developers in there. This may cover dependencies like serde and snafu
but will not hit any CosmWasm-related modules, so we look to bootstrap a very focused
review community.