Hi,
String hash is randomized, but not the integer hash:
$ python3.5 -c 'print(hash("abc"))'
-8844814677999896014
$ python3.5 -c 'print(hash("abc"))'
-7757160699952389646
$ python3.5 -c 'print(hash(1))'
1
$ python3.5 -c 'print(hash(1))'
1
frozenset hash is combined from values of the set. So it's only
randomized if values hashes are randomized.
The denial of service is more likely to occur with strings as keys,
than with integers.
See the following link for more information:
http://python-security.readthedocs.io/vuln/cve-2012-1150_hash_dos.html
Victor
2018年05月16日 17:48 GMT-04:00 Anthony Flury via Python-Dev <[email protected]>:
This may be known but I wanted to ask this esteemed body first.
I understand that from Python3.3 there was a security fix to ensure that
different python processes would generate different hash value for the same
input - to prevent denial of service based on crafted hash conflicts.
I opened two python REPLs on my Linux 64bit PC and did the following
Terminal 1:
>>> hash('Hello World')
-1010252950208276719
>>> hash( frozenset({1,9}) )
-7625378979602737914
>>> hash(frozenset({300,301}))
-8571255922896611313
>>> hash((1,9))
3713081631926832981
>>> hash((875,932))
3712694086932196356
Terminal 2:
>>> hash('Hello World')
-8267767374510285039
>>> hash( frozenset({1,9}) )
-7625378979602737914
>>> hash(frozenset({300,301}))
-8571255922896611313
>>> hash((1,9))
3713081631926832981
>>> hash((875,932))
3712694086932196356
As can be seen - taking a hash of a string does indeed create a different
value between the two processes (as expected).
However the frozen set hash, the same in both cases, as is the hash of the
tuples - suggesting that the vulnerability resolved in Python 3.3 wasn't
resolved across all potentially hashable values. lI even used different
large numbers to ensure that the integers weren't being interned.
I can imagine that frozensets aren't used frequently as hash keys - but I
would think that tuples are regularly used. Since that their hashes are not
salted does the vulnerability still exist in some form ?.
--
--
Anthony Flury
email : *[email protected]*
Twitter : *@TonyFlury <https://twitter.com/TonyFlury/>*
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