From: Eric Biggers <ebiggers@kernel.org>
To: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: "open list:HARDWARE RANDOM NUMBER GENERATOR CORE"
<linux-crypto@vger.kernel.org>,
Herbert Xu <herbert@gondor.apana.org.au>,
Paul Crowley <paulcrowley@google.com>
Subject: Re: [PATCH v3 2/2] crypto: arm/aes - add some hardening against cache-timing attacks
Date: Fri, 19 Oct 2018 13:30:58 -0700 [thread overview]
Message-ID: <20181019203056.GC246441@gmail.com> (raw)
In-Reply-To: <CAKv+Gu9XJ0k82ZNPRirs3Qhda3375CUA8uhJmsK85=1a9VmaNQ@mail.gmail.com>
On Fri, Oct 19, 2018 at 01:41:35PM +0800, Ard Biesheuvel wrote:
> On 18 October 2018 at 12:37, Eric Biggers <ebiggers@kernel.org> wrote:
> > From: Eric Biggers <ebiggers@google.com>
> >
> > Make the ARM scalar AES implementation closer to constant-time by
> > disabling interrupts and prefetching the tables into L1 cache. This is
> > feasible because due to ARM's "free" rotations, the main tables are only
> > 1024 bytes instead of the usual 4096 used by most AES implementations.
> >
> > On ARM Cortex-A7, the speed loss is only about 5%. The resulting code
> > is still over twice as fast as aes_ti.c. Responsiveness is potentially
> > a concern, but interrupts are only disabled for a single AES block.
> >
>
> So that would be in the order of 700 cycles, based on the numbers you
> shared in v1 of the aes_ti.c patch. Does that sound about right? So
> that would be around 1 microsecond, which is really not a number to
> obsess about imo.
>
Correct, on ARM Cortex-A7 I'm seeing slightly over 700 cycles per block
encrypted or decrypted, including the prefetching.
- Eric
next prev parent reply other threads:[~2018-10-20 4:38 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-10-18 4:37 [PATCH v3 0/2] crypto: some hardening against AES cache-timing attacks Eric Biggers
2018-10-18 4:37 ` [PATCH v3 1/2] crypto: aes_ti - disable interrupts while accessing S-box Eric Biggers
2018-10-18 4:37 ` [PATCH v3 2/2] crypto: arm/aes - add some hardening against cache-timing attacks Eric Biggers
2018-10-19 5:41 ` Ard Biesheuvel
2018-10-19 9:54 ` Ard Biesheuvel
2018-10-19 20:39 ` Eric Biggers
2018-10-20 2:34 ` Ard Biesheuvel
2018-10-19 20:30 ` Eric Biggers [this message]
2018-11-09 9:49 ` [PATCH v3 0/2] crypto: some hardening against AES " Herbert Xu
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