[][src]Module cargo_crev::doc::user::getting_started

Getting Started Guide


The goal of this guide is to introduce you to the crev review system, the cargo crev command, ideas behind them and describe the basic workflows that will allow you to start using them.

Please remember that crev project is still largely a work in progress, and this documentation might be incorrect or stale. In case of any problems please don't hesitate to join crev's gitter channel and ask for help or open a GitHub issue.

Any help in improving this documentation is greatly appreciated.

crev vs cargo-crev

crev is a general system of preparing cryptographically signed documents (proofs) describing results of code reviews and circulating them between developers to coordinate a distributed ecosystem of code review.

While crev itself is generic and abstract, to be a practical tool it requires integration with the given ecosystem of each programming language. cargo-crev is an implementation of crev for Rust programming language, tightly integrated with its package manager: cargo. The goal of cargo-crev is helping Rust community verify and review all the dependencies published on http://crates.io and used by Rust developers.

cargo-crev is a command line tool, similar in nature to tools like git. Integration with IDEs and text editors are possible, but not implemented at the moment.


cargo-crev is written in Rust, and until binaries for various operating systems are available, the recommended way to install it is installing from source.

Using static binaries

Static binaries build by CI pipeline are available on crev's releases GitHub page.

Building from source


Regrettably cargo-crev requires a non-Rust dependency to compile, as OpenSSL is required for TLS support.

Though OpenSSL is popular and readily available, it's virtually impossible to cover installing it on all the available operating systems. In case of problems, don't hesitate to ask for help.


The following should work on Ubuntu:

sudo apt-get install openssl libssl-dev

and should have matching command in the Unix-like OS of your choice.


To compile and install latest cargo-crev release use cargo:

cargo install cargo-crev

In case you'd like to try latest features from the master branch, try:

cargo install --git https://github.com/crev-dev/cargo-crev/ cargo-crev

If you need help installing Rust compiler & cargo, consider using rustup.rs page


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 build-in help

When installed cargo-crev can be run like this:

$ cargo crev
cargo-crev 0.9.0
Dawid Ciężarkiewicz <dpc@dpc.pw>
Scalable, social, Code REView system that we desperately need - Rust/cargo frontend

    cargo-crev crev <SUBCOMMAND>

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

    config    Config
    crate     Crate related operations (review, verify...)
    help      Prints this message or the help of the given subcommand(s)
    id        Id (own and of other users)
    repo      Proof Repository - store of proofs

As you can see, by default cargo crev displays the built in help. Try it and scan briefly over SUBCOMMANDS section. It should give you a good overview of the available functionality.


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 crate verify
status reviews     downloads    own. issues lines  geiger flgs crate                version         latest_t
none    0  0   354897   1504220 0/5    0/0   2249     504      core-foundation      0.5.1
none    0  0   530853   1026015 0/1    0/0    429       2      scoped_threadpool    0.1.9
none    0  0  1045209   2648161 1/1    0/0    403       3      same-file            1.0.4
none    0  0   395480  11267511 1/3    0/0   9563       0 CB   serde                1.0.90

Note: You can abbreviate most of cargo-crev subcommands. So you can save some keypresses with: cargo crev c v.

The actual output is using color to make the data more accessible.

The meaning of each column, and all the available options are described in the output of cargo crev crate verify --help command.

Right now we will discuss just the most important 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 it has been reviewed by enough trusted people to consider it trustworthy.

Verification of dependencies is considered as successful only if all the values in trust 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.

Fetching reviews from other users

The easiest way to verify packages is to see if other people did that before.

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.

Go ahead and re-run cargo crev crate verify. Chances are you're using crates that dpc have already reviewed. The reviews column will contain values bigger than zero.

Building trust proofs

Right now none of your crates is considered trusted yet, despite the fact that dpc might have reviewed them already. The reason is: you don't trust this user.

For most projects it is not possible to review all dependencies by yourself. You will have to trust some people. Let's crate a trust proof for dpc. You can always revoke this trust later if you wish.

$ cargo crev id trust FYlr8YoYGVvDwHQxqEIs89reKKDy-oWisoO0qXXEfHE
Error: User config not-initialized. Use `crev id new` to generate CrevID.

Oops. That's right. You can't sign a proof until you have your own identity.

Creating a CrevID

To create a CrevID you'll first need a github repository to serve as your public proof repository. Customarily the repository should be called crev-proofs.

  • GitHub users can just fork a template.
  • Other users can do it manually. Note: cargo-crev requires the master branch to already exist, so the repository you have created 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

Now, back to creating a trust proof for dpc.

$  cargo crev id trust FYlr8YoYGVvDwHQxqEIs89reKKDy-oWisoO0qXXEfHE
Enter passphrase to unlock:

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: ""

# # Creating Trust Proof
# A Trust Proof records your trust in abilities and standards of another
# entity using `crev` system.
# ## Responsibility
# While `crev` does not directly expose you to any harm from
# entities you trust, adding untrustworthy entities into your
# Web of Trust, might lower your overal security and/or reputation.
# On the other hand, the more trustworthy entites in your Web of Trust,
# the broader the reach of it and more data it can find.
# Your Proofs are cryptographically signed and will circulate in the ecosystem.
# While there is no explicit or implicity legal responsibiltity attached to
# using `crev` system, other people will most probably use it to judge you,
# your other work, etc.
# ## Data fields
# * `date` - proof timestamp
# * `from` - proof author
# * `ids` - objects of the trust relationship
# * `trust` - trust level; possible values:
#   * `high` - "for most practically purposes, I trust this ID as much or more
#              than myself" eg. "my dayjob ID", "known and reputatable expert",
#              "employee within my team"
#   * `medium` - typical, normal level of trust
#   * `low` - "I have some reservations about trusting this entity"
#   * `none` - "I don't actually trust this entity"; use to overwrite trust from
#              a previously issued Trust Proof
#   * `distrust` - "I distrust this person and so should you"
# * `comment` - human-readable information about this trust relationship,
#              (eg. who are these entities, why do you trust them)
# ## Further reading
# See https://github.com/crev-dev/cargo-crev/wiki/Howto:-Create-Review-Proofs wiki
# page for more information and Frequently Asked Questions, or join
# https://gitter.im/dpc/crev discussion channel.

Editing the proof is modeled after editing a commit message through git commit. As you can see helpful documentation is available in the editor. Don't forget to read it at some point.

When creating a trust proof you have to decide on the trust level, and optionally add a comment about the nature of this trust relationship.

Transitive effective trust

When you are done, have saved the proof and closed the editor, you should be able 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.

Fetching updates

Now that your Web of Trust (WoT) is built, you can fetch proofs from all the new and existing trusted users with:

$ cargo crev repo fetch trusted
Fetching https://github.com/oherrala/crev-proofs... OK
Fetching https://github.com/dpc/crev-proofs... OK

You can also consider fetching proofs from all the users crev is aware of - even ones that are not par of your WoT. Use cargo crev repo fetch all for that.

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 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/github.com-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>.

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 paramter 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.

After reviewing the code use the standard cargo crev crate review <cratename> to create the review proof.

Editing review proof

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

# Package Review of default 0.1.2
  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 implicity 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.

The most important part is: just be truthful.

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

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

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 and easy to parse. 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"
  id-type: crev
  id: 2CxdPgo2cbKpAfaPmEjMXJnXa7pdQGBBeGsgXjBJHzA
  url: "https://github.com/YOUR-USERNAME/crev-proofs"
  source: "https://crates.io"
  name: default
  version: 0.1.2
  revision: 583039a6a4233b6aa64dcba7a23f5ae4419a9a72
  digest: YuxzyXhCHZYMi4__Hj_hCzkQyxRLrZjDqL8usLqA4QY
  thoroughness: low
  understanding: medium
  rating: positive


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 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 them 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.


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 advise and are visible in the advisr output of verify.