linux-kernel - Question on ext4 directory hashes in combination with file name encryption

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Message-ID: <9a5198b3-0c00-a558-5132-9c38b4bb8795@nod.at>
Date:   Fri, 30 Sep 2016 16:09:09 +0200
From:   Richard Weinberger <richard@....at>
To:     linux-ext4@...r.kernel.org,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Cc:     Theodore Ts'o <tytso@....edu>, Eric Biggers <ebiggers@...gle.com>,
        David Gstir <david@...ma-star.at>
Subject: Question on ext4 directory hashes in combination with file name
 encryption

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