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Revert "switch to md5; adjust format a bit" 

This reverts commit d027ce144b.
This commit is contained in:
Benjamin Peterson 2017-09-07 12:26:21 -07:00
parent d027ce144b
commit 70b6d5aac9
1 changed files with 8 additions and 6 deletions
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pep-0552.txt
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@ -59,12 +59,13 @@ Python will begin to recognize two magic number variants for every pyc
version. One magic number will correspond to the current pyc format and the version. One magic number will correspond to the current pyc format and the
other to "hash-based" pycs introduced by this PEP. other to "hash-based" pycs introduced by this PEP.
In hash-based pycs, the second 32-bit field in the pyc header (currently the In hash-based pycs, the second field in the pyc header (currently the
"timestamp" field) will become a bitset of flags. We define the lowest flag in "timestamp" field) will contain the SipHash_ (with a hardcoded key) of the
this bitset called ``check_source``. This bitset field is followed by a 128-bit contents of the source file. Another a fast hash like MD5 or BLAKE2_ would also
MD5 hash field. We choose MD5 because it is fast and sufficiently collision work. We choose SipHash because Python already has a builtin implementation of
resistant for this application. No strong security properties are required it from :pep:`456`. The third field in the pyc header (currently the "source
here. (A truncated BLAKE2_ hash would also work.) size" field) will become a bitset of flags. We define the lowest flag in this
bitset called ``check_source``
When Python encounters a hash-based pyc, its behavior depends on the setting of When Python encounters a hash-based pyc, its behavior depends on the setting of
the ``check_source`` flag. If the ``check_source`` flag is set, Python will the ``check_source`` flag. If the ``check_source`` flag is set, Python will
@ -93,6 +94,7 @@ References
.. _reproducible build: https://reproducible-builds.org/ .. _reproducible build: https://reproducible-builds.org/
.. _Bazel: https://bazel.build/ .. _Bazel: https://bazel.build/
.. _BLAKE2: https://blake2.net/ .. _BLAKE2: https://blake2.net/
.. _SipHash: https://131002.net/siphash/
.. [#frozensets] http://benno.id.au/blog/2013/01/15/python-determinism .. [#frozensets] http://benno.id.au/blog/2013/01/15/python-determinism
.. [#interning] http://bugzilla.opensuse.org/show_bug.cgi?id=1049186 .. [#interning] http://bugzilla.opensuse.org/show_bug.cgi?id=1049186
.. _magic number: https://docs.python.org/3/library/importlib.html#importlib.util.MAGIC_NUMBER .. _magic number: https://docs.python.org/3/library/importlib.html#importlib.util.MAGIC_NUMBER