A "pip install" that is cryptographically guaranteed repeatable

## Peep

Deploying Python projects has long been a source of frustration for the security-conscious: a compromise of PyPI or its third-party CDN could get you a package different from the one you signed up for. To guarantee known-good dependencies for your deployments, you had to run a local package index, manually uploading packages as you vetted them, maintaining a set of ACLs for that server, and trying to somehow keep an audit trail of who did what. Alternatively, you could check everything into a vendor library, but that meant a lot of fooling around with your VCS (or maintaining custom tooling) to do upgrades.

Peep fixes all that.

Vet your packages, and put hashes of the PyPI-sourced tarballs into requirements.txt, like this:

# sha256: L9XU_-gfdi3So-WEctaQoNu6N2Z3ZQYAOu4-16qor-8

# sha256: qF4YU3XbdcEJ-Z7N49VUFfA15waKgiUs9PFsZnrDj0k
Jinja2==2.6

Then, use peep install instead of pip install, and let the crypto do the rest. If a downloaded package doesn’t match the expected hash, Peep will freak out, and installation will go no further.

There are no servers to maintain, no enormous vendor libs to wrestle, and no need to trust a package author’s key management practices. With the addition of a few hashes to your requirements file, you can know that your chain of trust is safely rooted in your own source tree.

### Switching to Peep

1. Install Peep:

pip install peep

(Or, better, embed peep.py into your codebase as described in the Embedding section below. That eliminates having to trust an unauthenticated PyPI download, assuming you manually vet peep.py itself the first time.)

2. Use Peep to install your project once:

cd yourproject
peep install -r requirements.txt

You’ll get output like this:

<a bunch of pip output>

The following packages had no hashes specified in the requirements file,
which leaves them open to tampering. Vet these packages to your
satisfaction, then add these "sha256" lines like so:

# sha256: L9XU_-gfdi3So-WEctaQoNu6N2Z3ZQYAOu4-16qor-8

# sha256: qF4YU3XbdcEJ-Z7N49VUFfA15waKgiUs9PFsZnrDj0k
Jinja2==2.6

# sha256: u_8C3DCeUoRt2WPSlIOnKV_MAhYkc40zNZxDlxCA-as
Pygments==1.4

# sha256: A1gwhyCNozcxug18_9RjJTmJQa1rctOt-AnP7_yR0PM

-------------------------------
Not proceeding to installation.
3. Vet the packages coming off PyPI in whatever way you typically do. For instance, read them, or compare them with known-good local copies.

4. Add the recommended hash lines to your requirements.txt, each one directly above the requirement it applies to. (The hashes are of the original, compressed tarballs from PyPI.)

5. In the future, always use peep install to install your requirements. You are now cryptographically safe!

### The Fearsome Warning

If, during installation, a hash doesn’t match, Peep will say something like this:

THE FOLLOWING PACKAGES DIDN'T MATCH THE HASHES SPECIFIED IN THE
REQUIREMENTS FILE. If you have updated the package versions, update the
hashes. If not, freak out, because someone has tampered with the packages.

requests: expected FWvz7Ce6nsfgz4--AoCHGAmdIY3kA-tkpxTXO6GimrE
got YhddA1kUpMLVODNbhIgHfQn88vioPHLwayTyqwOJEgY

It will then exit with a status of 1. Freak out appropriately.

### Other Features

• Peep implicitly turns on pip’s --no-deps option so unverified dependencies of your requirements can’t sneak through.

• All non-install commands just fall through to pip, so you can use Peep all the time if you want. This comes in handy for existing scripts that have a big \$PIP=/path/to/pip at the top.

• Peep-compatible requirements files remain entirely usable with pip, because the hashes are just comments, after all.

• Have a manually downloaded package you’ve vetted? Run peep hash on its tarball (the original, from PyPI–be sure to keep it around) to get its hash line:

% peep hash nose-1.3.0.tar.gz
# sha256: TmPMMyXedc-Y_61AvnL6aXU96CRpUXMXj3TANP5PUmA
• If a package is already present–which might be the case if you’re installing into a non-empty virtualenv–Peep doesn’t bother downloading or building it again. It assumes you installed it with Peep in a previous invocation and thus trusts it. The only exception to this is for URL-specified requirements where the URL contains a SHA-like filename (eg https://github.com/foo/bar/archive/<SHA>.zip), since the package version number is typically not incremented for every commit, so Peep cannot be sure the contents have not changed. Note: Re-using a virtualenv during deployment can really speed things up, but you will need to manually remove dependencies that are no longer in the requirements file.

• peep port converts a peep-savvy requirements file to one compatible with pip 8’s new hashing functionality:

% peep port requirements.txt
certifi==2015.04.28 \
--hash=sha256:268fa00c27de756d71663dd61f73a4a8d8727569bb1b474b2ce6020553826872 \
--hash=sha256:99785e6cf715cdcde59dee05a676e99f04835a71e7ced201ca317401c322ba96
click==4.0 --hash=sha256:9ab1d313f99b209f8f71a629f36833030c8d7c72282cf7756834baf567dca662

Note that comments and URLs don’t make it through, but the hard part—hash format conversion—is taken care of for you.

### Security and Insecurity

You get repeatability. If you peep install package Foo==1.2.3, every subsequent install of Foo==1.2.3 will be the same as the original (or Peep will complain).

Peep does not magically vet your packages. Peep is not a substitute for combing through your packages for malicious code or comparing them with known-good versions. If you don’t vet them, they are not vetted.

Peep does not make authors or indices trustworthy. All Peep does is guarantee that subsequent downloads of Foo==1.2.3 are the same as the first one. It doesn’t guarantee the author of that package is trustworthy. It doesn’t guarantee that the author of that package is the one who released that package. It doesn’t guarantee that the package index is trustworthy.

### Troubleshooting

#### Multiple Hashes: Architecture-Specific Packages and Old Versions of PyPI

Are you suddenly getting the Fearsome Warning? Maybe you’re really in trouble, but maybe something more innocuous is happening.

If your packages install from wheels or other potentially architecture-specific sources, their hashes will obviously differ across platforms. If you deploy on more than one, you’ll need more than one hash.

Also, some packages offer downloads in multiple formats: for example, zips and tarballs, or zips and wheels. Which version gets downloaded can vary based on your version of pip, meaning some packages may effectively have more than one valid hash.

To support these scenarios, you can stack up multiple known-good hashes above a requirement, as long as they are within a contiguous block of commented lines:

# Tarball:
# sha256: lvpN706AIAvoJ8P1EUfdez-ohzuSB-MyXUe6Rb8ppcE
#
# And the zip file:
# sha256: 6QTt-5DahBKcBiUs06BfkLTuvBu1uF7pblb_bPaUONU
mock==0.8.0

If you don’t want to wait until you’re bitten by this surprise, use the peep hash command to find hashes of each equivalent archive for a package. I like to vet one of them (say, the tarball), then download the others and use a file comparison tool to verify that they have identical contents. Then I run peep hash over both original archives, like so, and add the result to my requirements.txt:

% peep hash mock-0.8.0.tar.gz mock-0.8.0.zip
# sha256: lvpN706AIAvoJ8P1EUfdez-ohzuSB-MyXUe6Rb8ppcE
# sha256: 6QTt-5DahBKcBiUs06BfkLTuvBu1uF7pblb_bPaUONU

#### Upgrading Wheels with Old Versions of pip

If you’re reusing a virtualenv and using Peep with pip <6.0, then you should avoid using wheels. Otherwise, the old version of a package will not be entirely removed before the new one is installed, due to https://github.com/pypa/pip/issues/1825.

If you’re using pip 1.4, don’t pass the --use-wheel argument.

If you’re using pip 1.5, pass the --no-use-wheel argument.

### Version History

3.1.2
• Fix compatibility with pip 8.1.2. (abbeyj)

3.1.1
• The “peep had a problem” traceback is no longer output for several cases of pip installation errors that were not peep’s fault: for instance, the specified package version or requirements file not existing.

• peep port now emits URLs for URL-based requirements, if you’re using pip 6.1.0 or greater. (jotes)

3.1
• Print the name each new requirements file we encounter during peep port. This helps untangle the mess if your files use includes. (pmac)

• Always put hashes on their own lines, even if there’s only one. (pmac)

3.0
• Add support for pip 8.x.

• Drop support for the --allow-external, --allow-unverified and --allow-all-external arguments (for compatibility with pip 8).

• Drop support for Python 3.1/3.2.

2.5
• Support pip 7.x, through the currently latest 7.1.2, working around its buggy line counting. (kouk)

• Add peep port command to facilitate the transition to pip 8’s hashing.

• Fix bug in which the right way to call parse_requirements() would not be autodetected.

2.4.1
• Tolerate pip.__version__ being missing, which can apparently happen in arcane situations during error handling, obscuring informative tracebacks.

• Fix flake8 warnings again, and add flake8 to Travis runs.

2.4
• Add support for flags in the requirements file, pip-style, such as specifying alternative indices with -i.

• Remove a duplicate #egg= segment from an error message.

2.3
• Copy the operative portion of the MIT license into peep.py so embedding it doesn’t break the license.

• Fix flake8 linter warnings.

• Make peep compatible with pip v6.1.0+.

• Add tests against pip 6.0.8, 6.1.0, and 6.1.1 to the tox config.

• Run full set of tox tests on Travis.

2.2

• Remove extra skipped lines from the output.

• Add tests against pip 6.0.7 to the tox config.

2.1.2
• Get rid of repetition of explanatory messages at the end of a run when one applies to multiple packages.

2.1.1
• Fix bug in which peep would not upgrade a package expressed in terms of a GitHub-dwelling zip file if its version had not changed.

• Add tests against pip 6.0.4, 6.0.5, and 6.0.6 to the tox config.

2.1
• Support pip 6.x.

• Make error reporting friendly, emitting a bug reporting URL and environment info along with the traceback.

2.0

• Refactor significantly for comprehensibility.

• Drastically improve test coverage.

• Note that HTTPS certs are no longer checked. This shouldn’t matter, given our hash checks.

1.4

• Add the beginnings of a test suite.

• Treat package names in requirements files as case-insensitive, like pip.

1.3
• Pass through most args to the invocation of pip install that actually installs the downloaded archive. This means you can use things like --install-options fruitfully.

• Add Python 3.4 support by correcting an import.

• Install a second peep script named after the active Python version, e.g. peep-2.7. This is a convenience for those using multiple versions of Python and not using virtualenvs.

1.2
• Support GitHub-style tarballs (that is, ones whose filenames don’t contain the distro name or version and whose version numbers aren’t reliable) in requirements files. (Will Kahn-Greene)

• Warn when a URL-based requirement lacks #egg=. (Chris Adams)

1.1
• Support Python 3. (Keryn Knight)

1.0.2
• Add support for .tar.bz2 archives. (Paul McLanahan)

1.0.1
• Fix error (which failed safe) installing packages whose distro names contain underscores. (Chris Ladd)

1.0
• Add wheel support. Peep will now work fine when pip decides to download a wheel file. (Paul McLanahan)

0.9.1
• Don’t crash when trying to report a missing hash on a package that’s already installed.

0.9
• Put the operative parts of peep into a single module rather than a package, and make it directly executable. (Brian Warner)

0.8
• Support installing into non-empty virtualenvs, for speed. We do this by trusting any already-installed package which satisfies a requirement. This means you no longer have to rebuild lxml, for instance, each time you deploy.

• Wrap text output to 80 columns for nicer word wrap.

0.7

Make some practical tweaks for projects which bootstrap their trust chains by checking a tarball of peep into their source trees.

• Start supporting versions of pip back to 0.6.2 (released in January 2010). This way, you can deploy trustworthily on old versions of RHEL just by checking a tarball of peep into your source tree and pip-installing it; you don’t have to check in pip itself or go to the bother of unpacking the peep tarball and running python setup.py install from your deploy script.

• Remove the explicit dependency on pip. This is so a blithe call to pip install peep.tar.gz without --no-deps doesn’t go out and pull an untrusted package from PyPI. Instead, we scream at runtime if pip is absent or too old. Fail safe.

0.6

• Require pip>=1.2, as lower versions have a bug that causes a crash on peep install.

0.5
0.4
• Rework how peep downloads files and determines versions so we can tolerate PEP-386-noncompliant package version numbers. This amounted to a minor rewrite.

• Remove indentation from hash output so you don’t have to dedent it after pasting it into requirements.txt.

0.3
• Support Windows and other non-Unix OSes.

• The hash output now includes the actual version numbers of packages, so you can just paste it straight into your requirements.txt.

0.2.1
• Add a shebang line so you can actually run peep after doing pip install peep. Sorry, folks, I was doing setup.py develop on my own box.

0.2
• Fix repeated-logging bug.

• Fix spurious error message about not having any requirements files.

• Pass pip’s exit code through to the outside for calls to non-install subcommands.

• Improve spacing in the final output.

0.1
• Proof of concept. Does all the crypto stuff. Should be secure. Some rough edges in the UI.

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