linux-ext4 - Re: [f2fs-dev] [PATCH] fscrypt: use 32 bytes of encrypted filename

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Message-ID: <CAMHSBOWCf4gy9ApNvuyYMWUr-UAZscTArS=x3aAD4ohSgMq3_g@mail.gmail.com>
Date:   Fri, 21 Apr 2017 10:21:16 -0700
From:   Gwendal Grignou <gwendal@...omium.org>
To:     Eric Biggers <ebiggers3@...il.com>
Cc:     Jaegeuk Kim <jaegeuk@...nel.org>,
        Ryo Hashimoto <hashimoto@...omium.org>,
        Eric Biggers <ebiggers@...gle.com>,
        linux-f2fs-devel@...ts.sourceforge.net,
        linux-fscrypt@...r.kernel.org, linux-mtd@...ts.infradead.org,
        "Theodore Ts'o" <tytso@....edu>, linux-ext4@...r.kernel.org,
        Kazuhiro Inaba <kinaba@...omium.org>
Subject: Re: [f2fs-dev] [PATCH] fscrypt: use 32 bytes of encrypted filename

>
> In any case, I guess that unless there are other ideas we can do these patches:
>
> 1.) f2fs patch to start checking the name, as above
> 2.) patch to start encoding last 32 bytes of the name (or second-to-last CTS
>     block, I haven't decided yet) rather than last 16 bytes, changing
>     fs/crypto/, fs/ext4/, and fs/f2fs/

Using second-to-last CTS block is CTS-CBC specific. If we use another
method to encode filename (I am thinking of HEH,
http://www.mail-archive.com/linux-crypto@vger.kernel.org/msg21826.html)
that may not work anymore.
We don't have to use the last 32 bytes: using for instance the last 24
should be good enough, the escape rate will be 1/2^64 instead 1/2^128.

Gwendal.

> 3.) cleanup patches to introduce helper function and switch ext4 and f2fs to it
>
> (1) and (2) will be backported.
>
> UBIFS can be changed to use the helper function later if needed.  It's not as
> important for it to be backported there since UBIFS does the "double hashing",
> and UBIFS encryption was just added in 4.10 anyway.
>
> I can try to put together the full series when I have time.  It probably would
> make sense for it to go through the fscrypt tree, given the dependencies.
>
> Eric