[Distutils] Surviving a Compromise of PyPI - PEP 458 and 480

Vladimir Diaz vladimir.v.diaz at gmail.com
Thu Dec 11 04:16:48 CET 2014

Hello everyone,

I am a research programmer at the NYU School of Engineering.  My colleagues
(Trishank Kuppusamy and Justin Cappos) and I are requesting community
feedback on our proposal, "Surviving a Compromise of PyPI."  The two-stage
proposal can be reviewed online at:

PEP 458

PEP 480

Summary of the Proposal:

"Surviving a Compromise of PyPI" proposes how the Python Package Index
(PyPI) can be amended to better protect end users from altered or malicious
packages, and to minimize the extent of PyPI compromises against affected
users.  The proposed integration allows package managers such as pip to be
more secure against various types of security attacks on PyPI and defend
end users from attackers responding to package requests. Specifically,
these PEPs describe how PyPI processes should be adapted to generate and
incorporate repository metadata, which are signed text files that describe
the packages and metadata available on PyPI.  Package managers request
(along with the packages) the metadata on PyPI to verify the authenticity
of packages before they are installed.  The changes to PyPI and tools will
be minimal by leveraging a library, The Update Framework
<https://github.com/theupdateframework/tuf>, that generates and
transparently validates the relevant metadata.

The first stage of the proposal (PEP 458
<http://legacy.python.org/dev/peps/pep-0458/>) uses a basic security model
that supports verification of PyPI packages signed with cryptographic keys
stored on PyPI, requires no action from developers and end users, and
protects against malicious CDNs and public mirrors. To support continuous
delivery of uploaded packages, PyPI administrators sign for uploaded
packages with an online key stored on PyPI infrastructure. This level of
security prevents packages from being accidentally or deliberately tampered
with by a mirror or a CDN because the mirror or CDN will not have any of
the keys required to sign for projects.

The second stage of the proposal (PEP 480
<http://legacy.python.org/dev/peps/pep-0480/>) is an extension to the basic
security model (discussed in PEP 458) that supports end-to-end verification
of signed packages. End-to-end signing allows both PyPI and developers to
sign for the packages that are downloaded by end users.  If the PyPI
infrastructure were to be compromised, attackers would be unable to serve
malicious versions of these packages without access to the project's
developer key.  As in PEP 458, no additional action is required by end
users.  However, PyPI administrators will need to periodically (perhaps
every few months) sign metadata with an offline key.  PEP 480 also proposes
an easy-to-use key management solution for developers, how to interface
with a potential build farm on PyPI infrastructure, and discusses the
security benefits of end-to-end signing.  The second stage of the proposal
simultaneously supports real-time project registration and developer
signatures, and when configured to maximize security on PyPI, less than 1%
of end users will be at risk even if an attacker controls PyPI and goes
undetected for a month.

We thank Nick Coghlan and Donald Stufft for their valuable contributions,
and Giovanni Bajo and Anatoly Techtonik for their feedback.

PEP 458 & 480 authors.
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