Summary of the Proposal:
a Compromise of PyPI" proposes how the Python Package Index (PyPI) can
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
, that generates and transparently validates the relevant metadata.
The first stage of the proposal (PEP 458
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
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.
thank Nick Coghlan and Donald Stufft for their valuable contributions,
and Giovanni Bajo and Anatoly Techtonik for their feedback.
PEP 458 & 480 authors.