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Getting Started Guide

TL;DR

# setup
cargo install cargo-crev
cargo crev trust --level high https://github.com/dpc/crev-proofs
cargo crev repo fetch all

# verify
cargo crev verify --show-all

# review
cargo crev open $crate_name
cargo crev review $crate_name

# share reviews
# Fork this: https://github.com/crev-dev/crev-proofs/fork
cargo crev id set-url https://github.com/$your_github_username/crev-proofs
cargo crev publish

# get more reviews
cargo crev id query all
cargo crev trust # insert other people's URLs or Ids here

# review just the parts that changed since
cargo crev crate diff $crate_name | less
cargo crev review --diff $previous_version -- $crate_name

Introduction

Crev is a system for verifying security and reliability of dependencies based on collaborative code reviews. Crev users review source code of packages/libraries/crates, and share their findings with others. Crev then uses Web of Trust select trusted reviews and judge reputation of projects' dependencies.

Crev is language-independent, but the primary implementation is cargo crev for Rust/Cargo crates.

This project and documentation is a work in progress. If anything is missing, incorrect or stale, let us know. You can join crev's gitter channel and ask for help or open a GitHub issue. Any help in improving this documentation is greatly appreciated.

Installing

cargo-crev is a command-line tool written in Rust. You can download pre-built binaries from Releases page, or install from source:

cargo install cargo-crev

In case of compilation issues, check build instructions for more information and troubleshooting.

Running

In a similar way that git is typically used within a context of a local git repository, cargo crev is supposed to be used inside Rust cargo project. Before using cargo crev make sure to change current directory to a Rust project.

Using Subcommands

$ cargo crev
cargo-crev 0.18.0

USAGE:
    cargo crev <SUBCOMMAND>

FLAGS:
    -h, --help       Prints help information
    -V, --version    Prints version information

SUBCOMMANDS:
    config     Local configuration
    crate      Crate related operations (review, verify...)
    id         Id (own and of other users)
    proof      Find a proof in the proof repo
    repo       Proof Repository
    trust      Add a Trust proof by an Id or a URL
    goto       Shortcut for `crate goto`
    open       Shortcut for `crate open`
    publish    Shortcut for `repo publish`
    review     Shortcut for `crate review`
    update     Shortcut for `repo update`
    verify     Shortcut for `crate verify`

A subcommand determines the action taken by cargo-crev. Some subcommand of cargo-crev offer an additional level of subcommands. Some of these cascaded subcommands are provided by shortcuts, such as verify for crate verify. For specific help regarding a subcommand use the -h flag.

Note: You can abbreviate most cargo-crev subcommands. For example: cargo crev cr v.

Verifying

As a user, your typical goal of using cargo crev is verifying that all the dependencies of the current crate are trustworthy and free of serious bugs and flaws.

The list of dependencies and their current trustworthiness status is available through cargo crev crate verify command. This is one of the most important and commonly used sub-command.

Let's take a look:

$ cargo crev verify --show-all
status reviews issues owner      downloads    loc lpidx geiger flgs crate                version      latest_t
none     0   2  0   0  0  3   197K   5129K    179    84      0 CB__ wasm-bindgen-shared  0.2.70
none     0   1  0   0  0  1   497K   1603K    268    29      0 ____ bytesize             1.0.1
none     0   1  0   0  0  1  3459K   7936K    238    94      1 ____ subtle               1.0.0
none     0   0  0   0  0  3   120K    854K    167    50      0 ____ signature            1.3.0
none     2   2  0   0  0  1     9K      9K      3    15      0 ____ default              0.1.2

Columns

On the right side crate and version indicate for which crate (in a given version) values in other columns are calculated and displayed for.

The status column displays the verification status for each crate. A pass value indicates that it has been reviewed by a sufficient number of trusted peers. none for lacking reviews, flagged or dangerous for crates with problem reports. Verification of dependencies is considered as successful only if all the values in status column contain pass value.

If you just started using crev, your Rust project probably has more than 100 dependencies, and all of them are not passing the verification. That's the reason why crev was created - your software is implicitly trusting 100 or more libraries, created by strangers from the Internet, containing code that you've never looked at. It might seem like an impossible problem to solve, but the goal of crev is to actually make it doable.

cargo crev verify --help:

  • reviews - Number of reviews for the specific version and for all available versions (total)
  • issues - Number of issues repored (from trusted sources/all)
  • owner
    • In non-recursive mode: Owner counts from crates.io (known/all)
    • In recursive mode:
      • Total number of owners from crates.io
      • Total number of owner groups ignoring subsets
  • downloads - Download counts from crates.io for the specific version and all versions
  • loc - Lines of Rust code
  • lpidx - "left-pad" index (ratio of downloads to lines of code)
  • geiger - Geiger score: number of unsafe lines
  • flgs - Flags for specific types of packages
    • CB - Custom Build (runs arbitrary code at build time)
    • UM - Unmaintained crate
  • name - Crate name
  • version - Crate version
  • latest_t - Latest trusted version

Fetching reviews from other users

Reviews are stored in public git repositories of crev users. cargo crev update or cargo crev repo fetch trusted will automatically update known repositories. It's also possible to fetch them individually. Let's fetch all the proofs from the author of crev:

> cargo crev repo fetch url https://github.com/dpc/crev-proofs
Fetching https://github.com/dpc/crev-proofs... OK
Found proofs from:
      70 FYlr8YoYGVvDwHQxqEIs89reKKDy-oWisoO0qXXEfHE

This command does a git fetch from a publicly available proof repository of a git user, and stores it in a local cache for future use. A proof repository is just a git repository containing proofs.

Building trust proofs

It's possible that some crates have reviews, but the crates aren't trusted. This happens when you don't trust the reviewers.

For most projects it is not possible to review all dependencies by yourself. You will have to trust some people. The fact of trusting a crev user is publicly recorded as a trust proof. This allows building a public network of trusted reviewers.

You can trust a user specifically by their CrevID. This is the most secure option. To trust dpc, run:

$ cargo crev id trust FYlr8YoYGVvDwHQxqEIs89reKKDy-oWisoO0qXXEfHE

After you unlock your ID you'll be put into a text editor to create a proof:

# Trust for FYlr8YoYGVvDwHQxqEIs89reKKDy-oWisoO0qXXEfHE https://github.com/dpc/crev-proofs
trust: medium
comment: ""

You can edit it to customize the relationship. Editing the proof is modeled after editing a commit message through git commit. As you can see helpful documentation is available in the editor.

Creating a CrevID

You can also be a reviewer, and other people will be able to use your reviews. You will need a public git repository to serve as your proof repository. Customarily the repository should be called crev-proofs.

  • GitHub users can just fork a template (same for GitLab).
  • Other users can do it manually. Note: cargo-crev requires the master branch to already exist, so the repository you create has to contain at least one existing commit.

Then run cargo crev id new like this:

$ cargo crev id new --url https://github.com/YOUR-USERNAME/crev-proofs
https://github.com/YOUR-USERNAME/crev-proofs cloned to /home/YOUR-USERNAME/.config/crev/proofs/Sp87YXeDKUyh4jImm23bCp1Gr-6eNkMoQogWbftNobQ
CrevID will be protected by a passphrase.
There's no way to recover your CrevID if you forget your passphrase.
Enter new passphrase:

The command will ask you to encrypt your identity, and print out some encrypted data to back up. Please copy that data and store it somewhere reliable.

You can generate and use multiple IDs, but one is generally enough. Check your current CrevID like this:

$ cargo crev id current
2CxdPgo2cbKpAfaPmEjMXJnXa7pdQGBBeGsgXjBJHzA https://github.com/YOUR-USERNAME/crev-proofs

To push your changes (reviews, trust proofs) run:

cargo crev publish

Transitive effective trust

When you are done, have saved the proof and closed the editor, you should be able to query all the ids you trust.

$ cargo crev id query trusted
FYlr8YoYGVvDwHQxqEIs89reKKDy-oWisoO0qXXEfHE medium https://github.com/dpc/crev-proofs
YWfa4SGgcW87fIT88uCkkrsRgIbWiGOOYmBbA1AtnKA low    https://github.com/oherrala/crev-proofs
2CxdPgo2cbKpAfaPmEjMXJnXa7pdQGBBeGsgXjBJHzA high   https://github.com/YOUR-USERNAME/crev-proofs

That might be a little surprising. Not only are you trusting FYlr8YoYGVvDwHQxqEIs89reKKDy-oWisoO0qXXEfHE which you have just signed the trust proof for, but also some other user.

That's because user dpc already trusted user oherrala. Trust in crev is transitive. If you trust user b, and user b trusts user c, you're implicitly trusting user c. That is what your personal Web of Trust really means in crev.

For distrustful people, it seems scary at first, but it should not.

We are trying to achieve the "impossible" here. We're not going to get much done if we are not reusing work of other people. And we should use any help we can get.

If it still makes you worry, just be aware that cargo crev provides a lot of ways to configure the effective trust calculation, including control over depth of the Web of Trust and redundancy level required. Also, the effective transitive trust level of c is always lower or equal to the direct trust level of b.

Reviewing code

Try cargo crev crate verify again.

If you are moderately lucky, at least some of the dependencies are now passing the verification.

But ultimately someone has to do the review, and at least sometimes you will have to do it yourself.

Scan the output of cargo crev crate verify and pick a crate with low lines of code (loc) count. For your first review you want to start small and easy.

At the moment of writing this cargo crev provides two methods of reviewing crate source code:

  • for people preferring the command line and text editors like Vim, there's a cargo crev crate goto command
  • for IDE users cargo crev crate open

Reviewing code using cargo crev crate goto

If you want to review a crate called default, you run:

$ cargo crev crate goto default
Opening shell in: /home/YOUR-USERNAME/.cargo/registry/src/git.luolix.top-1ecc6299db9ec823/default-0.1.2
Use `exit` or Ctrl-D to return to the original project.
Use `review` and `flag` without any arguments to review this crate.

As the output explains: cargo crev crate goto works by opening a new shell with current working directory set to a copy of the crate source code stored by cargo itself.

You're now free to use Vim or any other commands and text editors to investigate the content of the crate. tree -alh or ls are a typical starting commands, followed by vi <path_to_rs_file>.

Also consider using cargo tree which is part of cargo as of cargo 1.44.0, cargo-audit and cargo-outdated.

Now go ahead and review! It might be a novel experience, but it is the core of crev - we can not build trust if no one ever actually reviews any code. Try to be thorough, but at the same time: do not push yourself too much or let the fear make you not review at all.

When you are done with the actual review, it is time to actually create and sign the review proof.

You either call cargo crev crate review (or cargo crev flag if results of your review were negative), or exit the temporary review-shell and use cargo crev review <cratename>.

Reviewing code using cargo crev open

If you are an IDE user you can make crev open the crate source code in the IDE of your choice.

Example. VSCode users can run:

$ cargo crev open <crate> --cmd "code --wait -n" --cmd-save

--cmd-save will make crev remember the --cmd parameter in the future, so it does not have to be repeated every time. The exact --cmd to use for each IDE can vary, and you can ask for help in figuring it out on the crev's gitter channel. You can change the command later with cargo crev config edit.

Creating a review

After reviewing the code, create the review proof:

cargo crev crate review <cratename>

Similarly to editing trust proof, you have to edit the review proof document when you create a review.

# Package Review of default 0.1.2
review:
  thoroughness: low
  understanding: medium
  rating: positive
comment: ""


# # Creating Package Review Proof
#
# A Package Review Proof records results of your review of a version/release
# of a software package.
#
# ## Responsibility
#
# It is important that your review is truthful. At very least, make sure
# to adjust the `thoroughness` and `understanding` correctly.
#
# Other users might use information you provide, to judge software quality
# and trustworthiness.
#
# Your Proofs are cryptographically signed and will circulate in the ecosystem.
# While there is no explicit or implicitly legal responsibiltity attached to
# using `crev` system, other people will most probably use it to judge you,
# your other work, etc.
#
#
# ## Data fields
#
(...)

Again, a helpful comment section documents the basic guidelines of review proof, read it here.

The most important part is: just be truthful.

Before you finish and save the proof, let us look at an existing, signed review proof

-----BEGIN CREV PACKAGE REVIEW-----
version: -1
date: "2018-12-19T22:00:24.644210896-08:00"
from:
  id-type: crev
  id: FYlr8YoYGVvDwHQxqEIs89reKKDy-oWisoO0qXXEfHE
  url: "https://github.com/dpc/crev-proofs"
package:
  source: "https://crates.io"
  name: either
  version: 1.5.0
  digest: uBbgCVotv_8z4SEOjremFmvMG4JPhUROC19OLjPPLNE
review:
  thoroughness: medium
  understanding: high
  rating: strong
comment: "Simple `Either` type."
-----BEGIN CREV PACKAGE REVIEW SIGNATURE-----
IBPz20fpI6x3nWJJ1pRsHqGVq3b6yQxyYppIlVPUEZIL3h9AYrV-u7UJMPu5sqCWski91mX8qOE5D3_2bgksDQ
-----END CREV PACKAGE REVIEW-----

As you might have already noticed, the document you are editing is not a complete review proof. A lot of details will be filled automatically by cargo crev.

crev proofs are Yaml documents, wrapped in GPG-like separators, and signed using the private key generated during cargo crev id new.

Yaml is a popular serialization format. It is easy to read. It also makes the document format easily extendable in the future.

Time to save the document and exit the editor.

You should now be able to see your proof in the output of cargo crev repo query review <cratename>:

$ cargo crev repo query review default
version: -1
date: "2019-06-19T23:32:13.683894969-07:00"
from:
  id-type: crev
  id: 2CxdPgo2cbKpAfaPmEjMXJnXa7pdQGBBeGsgXjBJHzA
  url: "https://github.com/YOUR-USERNAME/crev-proofs"
package:
  source: "https://crates.io"
  name: default
  version: 0.1.2
  revision: 583039a6a4233b6aa64dcba7a23f5ae4419a9a72
  digest: YuxzyXhCHZYMi4__Hj_hCzkQyxRLrZjDqL8usLqA4QY
review:
  thoroughness: low
  understanding: medium
  rating: positive

Congratulations!

Publishing your proofs

Every time you create a proof crev records it in a local copy of your proof repository associated with your current CrevID.

You can access this repository using cargo crev repo git command.

$ cargo crev repo git log
commit a308421882822bd2256574b6e966a114dd4bfc6e (HEAD -> master)
Author: You <your_email@example.org>
Date:   Wed Jun 19 23:44:20 2019 -0700

    Add review for default v0.1.2
(...)

When you are ready, you can push your recent proofs to your public repository with cargo crev repo publish.

Now that your work is public, the only thing left is to help other people find it. Until someone creates a trust proof for your CrevId (even with trust: none settings), your proof repository is not easily discoverable.

You can ask other people to include your CrevID in their WoT by publishing a blog-post, sending a tweet, sending message on crev's gitter channel or adding it to the official bootstrapping wiki-page list of crev proof repositories

You can also use these places to find more proof repositories of other people.

Follow-up

This short guide is just meant to get you started.

There's already more functionality implemented in cargo crev, and even more will be continuously added in the future. Notably:

  • If you plan to share a CrevId between many computers, make sure to try export and import commands.
  • Differential reviews are available, where instead of reviewing a whole crate, you can review a diff between already trusted and current version (diff and review --diff commands).
  • Security and serious flaws can be reported with review --advisory and are visible in the issues output of verify.