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Date:   Sun, 1 May 2022 11:37:40 -0700
From:   Eric Biggers <ebiggers@kernel.org>
To:     Nathan Huckleberry <nhuck@google.com>
Cc:     linux-crypto@vger.kernel.org, linux-fscrypt@vger.kernel.org,
        Herbert Xu <herbert@gondor.apana.org.au>,
        "David S. Miller" <davem@davemloft.net>,
        linux-arm-kernel@lists.infradead.org,
        Paul Crowley <paulcrowley@google.com>,
        Sami Tolvanen <samitolvanen@google.com>,
        Ard Biesheuvel <ardb@kernel.org>
Subject: Re: [PATCH v5 8/8] fscrypt: Add HCTR2 support for filename encryption
Message-ID: <Ym7TdNCe/3gXdVNr@sol.localdomain>
References: <20220427003759.1115361-1-nhuck@google.com>
 <20220427003759.1115361-9-nhuck@google.com>
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On Wed, Apr 27, 2022 at 12:37:59AM +0000, Nathan Huckleberry wrote:
> HCTR2 is a tweakable, length-preserving encryption mode that is intended
> for use on CPUs with dedicated crypto instructions.  HCTR2 has the
> property that a bitflip in the plaintext changes the entire ciphertext.
> This property fixes a known weakness with filename encryption: when two
> filenames in the same directory share a prefix of >= 16 bytes, with
> AES-CTS-CBC their encrypted filenames share a common substring, leaking
> information.  HCTR2 does not have this problem.
> 
> More information on HCTR2 can be found here: "Length-preserving
> encryption with HCTR2": https://eprint.iacr.org/2021/1441.pdf
> 
> Signed-off-by: Nathan Huckleberry <nhuck@google.com>
> Reviewed-by: Ard Biesheuvel <ardb@kernel.org>

Acked-by: Eric Biggers <ebiggers@google.com>

- Eric