diff options
| author | Miss Islington (bot) <31488909+miss-islington@users.noreply.github.com> | 2020-11-21 09:12:21 (GMT) |
|---|---|---|
| committer | GitHub <noreply@github.com> | 2020-11-21 09:12:21 (GMT) |
| commit | 97136d71a78a4b6b816f7e14acc52be426efcb6f (patch) | |
| tree | 15f723a869c7c40d2f01e97e755b59f7ccc3acc6 /Misc/NEWS.d | |
| parent | 0762e09eb14269b38f60e1b58d2c7f36056a4694 (diff) | |
| download | cpython-97136d71a78a4b6b816f7e14acc52be426efcb6f.zip cpython-97136d71a78a4b6b816f7e14acc52be426efcb6f.tar.gz cpython-97136d71a78a4b6b816f7e14acc52be426efcb6f.tar.bz2 | |
bpo-40791: Make compare_digest more constant-time. (GH-20444)
* bpo-40791: Make compare_digest more constant-time.
The existing volatile `left`/`right` pointers guarantee that the reads will all occur, but does not guarantee that they will be _used_. So a compiler can still short-circuit the loop, saving e.g. the overhead of doing the xors and especially the overhead of the data dependency between `result` and the reads. That would change performance depending on where the first unequal byte occurs. This change removes that optimization.
(This is change GH-1 from https://bugs.python.org/issue40791 .)
(cherry picked from commit 31729366e2bc09632e78f3896dbce0ae64914f28)
Co-authored-by: Devin Jeanpierre <jeanpierreda@google.com>
Diffstat (limited to 'Misc/NEWS.d')
| -rw-r--r-- | Misc/NEWS.d/next/Security/2020-05-28-06-06-47.bpo-40791.QGZClX.rst | 1 |
1 files changed, 1 insertions, 0 deletions
diff --git a/Misc/NEWS.d/next/Security/2020-05-28-06-06-47.bpo-40791.QGZClX.rst b/Misc/NEWS.d/next/Security/2020-05-28-06-06-47.bpo-40791.QGZClX.rst new file mode 100644 index 0000000..69b9de1 --- /dev/null +++ b/Misc/NEWS.d/next/Security/2020-05-28-06-06-47.bpo-40791.QGZClX.rst @@ -0,0 +1 @@ +Add ``volatile`` to the accumulator variable in ``hmac.compare_digest``, making constant-time-defeating optimizations less likely.
\ No newline at end of file |