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Groups > linux.kernel > #1494123 > unrolled thread
| Started by | Richard Weinberger <richard@nod.at> |
|---|---|
| First post | 2016-09-30 16:10 +0200 |
| Last post | 2016-10-01 02:50 +0200 |
| Articles | 3 — 3 participants |
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Question on ext4 directory hashes in combination with file name encryption Richard Weinberger <richard@nod.at> - 2016-09-30 16:10 +0200
Re: Question on ext4 directory hashes in combination with file name encryption Andreas Dilger <adilger@dilger.ca> - 2016-09-30 22:30 +0200
Re: Question on ext4 directory hashes in combination with file name encryption Theodore Ts'o <tytso@mit.edu> - 2016-10-01 02:50 +0200
| From | Richard Weinberger <richard@nod.at> |
|---|---|
| Date | 2016-09-30 16:10 +0200 |
| Subject | Question on ext4 directory hashes in combination with file name encryption |
| Message-ID | <sn6FI-2MJ-5@gated-at.bofh.it> |
Hi, if I read the ext4 code correctly, you pass encrypted filenames to ext4fs_dirhash(). These filenames are not encoded and therefore binary gibberish. Isn't this a problem for the ext4 hash functions? My fear is that these hashes are optimized for ASCII strings and produce more collisions when binary data is used as input. Thanks, //richard
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| From | Andreas Dilger <adilger@dilger.ca> |
|---|---|
| Date | 2016-09-30 22:30 +0200 |
| Subject | Re: Question on ext4 directory hashes in combination with file name encryption |
| Message-ID | <sncBr-6LW-3@gated-at.bofh.it> |
| In reply to | #1494123 |
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On Sep 30, 2016, at 8:09 AM, Richard Weinberger <richard@nod.at> wrote: > > Hi, > > if I read the ext4 code correctly, you pass encrypted filenames to ext4fs_dirhash(). > These filenames are not encoded and therefore binary gibberish. > Isn't this a problem for the ext4 hash functions? My fear is that these hashes are optimized > for ASCII strings and produce more collisions when binary data is used as input. The default hash function (half-md4) is an (old) crypto hash and works fine with binary data. Some of the other hash functions are less strong, but I don't think anyone changes the hash function for ext4. Cheers, Andreas
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| From | Theodore Ts'o <tytso@mit.edu> |
|---|---|
| Date | 2016-10-01 02:50 +0200 |
| Message-ID | <sngF3-Vh-3@gated-at.bofh.it> |
| In reply to | #1494123 |
On Fri, Sep 30, 2016 at 04:09:09PM +0200, Richard Weinberger wrote: > > if I read the ext4 code correctly, you pass encrypted filenames to ext4fs_dirhash(). > These filenames are not encoded and therefore binary gibberish. That's correct. > Isn't this a problem for the ext4 hash functions? My fear is that these hashes are optimized > for ASCII strings and produce more collisions when binary data is used as input. I'm not particularly worried. In general, while the converse is true; that hashes that assume that they are used for binary data might not work as well for ASCII strings, the ext4 hash functions should work fine for binary data. - Ted
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