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Date: Tue, 20 Nov 2018 14:33:45 +0800
From: Herbert Xu <herbert@...dor.apana.org.au>
To: Eric Biggers <ebiggers@...nel.org>
Cc: linux-crypto@...r.kernel.org, linux-fscrypt@...r.kernel.org,
linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
Paul Crowley <paulcrowley@...gle.com>,
Greg Kaiser <gkaiser@...gle.com>,
"Jason A . Donenfeld" <Jason@...c4.com>,
Samuel Neves <samuel.c.p.neves@...il.com>,
Tomer Ashur <tomer.ashur@...t.kuleuven.be>
Subject: Re: [PATCH v4 00/14] crypto: Adiantum support
On Fri, Nov 16, 2018 at 05:26:17PM -0800, Eric Biggers wrote:
> Hello,
>
> We've been working to find a way to bring storage encryption to
> entry-level Android devices like the inexpensive "Android Go" devices
> sold in developing countries, and some smartwatches. Unfortunately,
> often these devices still ship with no encryption, since for cost
> reasons they have to use older CPUs like ARM Cortex-A7; and these CPUs
> lack the ARMv8 Cryptography Extensions, making AES-XTS much too slow.
>
> We're trying to change this, since we believe encryption is for
> everyone, not just those who can afford it. And while it's unknown how
> long CPUs without AES support will be around, there will likely always
> be a "low end"; and in any case it's immensely valuable to provide a
> software-optimized cipher that doesn't depend on hardware support.
> Lack of hardware support should not be an excuse for no encryption.
>
> But after an extensive search (e.g. see [1]) we were unable to find an
> existing cipher that simultaneously meets the very strict performance
> requirements on ARM processors, is secure (including having sufficient
> security parameters as well as sufficient cryptanalysis of any
> primitive(s) used), is suitable for practical use in dm-crypt and
> fscrypt, *and* avoids any particularly controversial primitive.
>
> Therefore, we (well, Paul Crowley did the real work) designed a new
> encryption mode, Adiantum. In essence, Adiantum makes it secure to use
> the ChaCha stream cipher for disk encryption. Adiantum is specified by
> our paper here: https://eprint.iacr.org/2018/720.pdf ("Adiantum:
> length-preserving encryption for entry-level processors"). Reference
> code and test vectors are here: https://github.com/google/adiantum.
> Most of the high-level concepts of Adiantum are not new; similar
> existing modes include XCB, HCTR, and HCH. Adiantum and these modes are
> true wide-block modes (tweakable super-pseudorandom permutations), so
> they actually provide a stronger notion of security than XTS.
>
> Adiantum is an improved version of our previous algorithm, HPolyC [2].
> Like HPolyC, Adiantum uses XChaCha12, two passes of an
> ε-almost-∆-universal (εA∆U) hash function, and one AES-256 encryption of
> a single 16-byte block. On ARM Cortex-A7, on 4096-byte messages
> Adiantum is about 4x faster than AES-256-XTS (about 5x for decryption),
> and about 30% faster than Speck128/256-XTS.
>
> Adiantum is a construction, not a primitive. Its security is reducible
> to that of XChaCha12 and AES-256, subject to a security bound; the proof
> is in Section 5 of our paper. Therefore, one need not "trust" Adiantum;
> they only need trust XChaCha12 and AES-256. Note that of these two
> primitives, AES-256 currently has the lower security margin.
>
> Adiantum is ~20% faster than HPolyC, with no loss of security; in fact,
> Adiantum's security bound is slightly better than HPolyC's. It does
> this by choosing a faster εA∆U hash function: it still uses Poly1305's
> εA∆U hash function, but now a hash function from the "NH" family of hash
> functions is used to "compress" the message by 32x first. NH is εAU (as
> shown in the UMAC paper[3]) but is over twice as fast as Poly1305. Key
> agility is reduced, but that's acceptable for disk encryption.
>
> NH is also very simple, and it's easy to implement in SIMD assembly,
> e.g. in ARM NEON. Now, to get good performance only a SIMD
> implementation of NH is required, not Poly1305. Therefore, Adiantum can
> be easier to port to new platforms than HPolyC, despite Adiantum's
> slightly increased complexity. For now this patchset only includes an
> ARM32 NEON implementation of NH, but as a proof of concept I've also
> written SSE2, AVX2, and ARM64 NEON implementations of NH; see
> https://github.com/google/adiantum/tree/master/benchmark/src.
>
> This patchset adds Adiantum to Linux's crypto API, focusing on generic
> and ARM32 implementations. Patches 1-9 add support for XChaCha20 and
> XChaCha12. Patches 10-13 add NHPoly1305 support, needed for Adiantum
> hashing. Patch 14 adds Adiantum support as a skcipher template.
>
> This patchset applies to cryptodev. It can also be found in git at
> branch "adiantum-v4" of:
> https://git.kernel.org/pub/scm/linux/kernel/git/ebiggers/linux.git
>
> With this patchset, Adiantum is already usable in dm-crypt via the
> "capi:" cipher syntax. I'll also be adding Adiantum support to fscrypt
> via the patch https://patchwork.kernel.org/patch/10669339/, but I
> dropped it from this series for now since it will be taken through the
> fscrypt git tree instead. Note that in fscrypt, Adiantum will also fix
> an information leak in filenames encryption when filenames share a
> common prefix, and Adiantum's long IV support make it safe to use the
> same key for many files, improving performance even more.
>
> Again, for more details please read our paper:
>
> Adiantum: length-preserving encryption for entry-level processors
> (https://eprint.iacr.org/2018/720.pdf)
>
> References:
> [1] https://www.spinics.net/lists/linux-crypto/msg33000.html
> [2] https://patchwork.kernel.org/cover/10558059/
> [3] https://fastcrypto.org/umac/umac_proc.pdf
>
> Changed since v3:
> - Rebase onto cryptodev because of recent ChaCha20 changes.
> - Drop fscrypt patch; I'm sending it as a standalone patch.
>
> Changed since v2:
> - Simplify the generic NH implementation.
> - Add patches to reduce atomic walks and disabling preemption.
> - Split Poly1305 changes into two patches.
> - Add tcrypt test mode for Adiantum.
> - Make NEON 'chacha_permute' a function rather than a macro.
> - Use .base.* style when declaring algorithms.
> - Replace BUG_ON() in chacha_permute() with WARN_ON_ONCE().
> - Set Adiantum instance {min,max}_keysize correctly in all cases.
> - Make the Adiantum template take the nhpoly1305 driver name as
> optional third argument (useful for testing).
>
> Thanks to Ard Biesheuvel for reviewing the patches.
>
> Changed since v1:
> - Replace HPolyC with Adiantum (uses a faster hash function).
> - Drop ARM accelerated Poly1305.
> - Add fscrypt patch.
>
> Eric Biggers (14):
> crypto: chacha20-generic - add HChaCha20 library function
> crypto: chacha20-generic - don't unnecessarily use atomic walk
> crypto: chacha20-generic - add XChaCha20 support
> crypto: chacha20-generic - refactor to allow varying number of rounds
> crypto: chacha - add XChaCha12 support
> crypto: arm/chacha20 - limit the preemption-disabled section
> crypto: arm/chacha20 - add XChaCha20 support
> crypto: arm/chacha20 - refactor to allow varying number of rounds
> crypto: arm/chacha - add XChaCha12 support
> crypto: poly1305 - use structures for key and accumulator
> crypto: poly1305 - add Poly1305 core API
> crypto: nhpoly1305 - add NHPoly1305 support
> crypto: arm/nhpoly1305 - add NEON-accelerated NHPoly1305
> crypto: adiantum - add Adiantum support
>
> arch/arm/crypto/Kconfig | 7 +-
> arch/arm/crypto/Makefile | 6 +-
> ...hacha20-neon-core.S => chacha-neon-core.S} | 98 +-
> arch/arm/crypto/chacha-neon-glue.c | 201 ++
> arch/arm/crypto/chacha20-neon-glue.c | 127 -
> arch/arm/crypto/nh-neon-core.S | 116 +
> arch/arm/crypto/nhpoly1305-neon-glue.c | 77 +
> arch/arm64/crypto/chacha20-neon-glue.c | 40 +-
> arch/x86/crypto/chacha20_glue.c | 48 +-
> arch/x86/crypto/poly1305_glue.c | 20 +-
> crypto/Kconfig | 46 +-
> crypto/Makefile | 4 +-
> crypto/adiantum.c | 658 ++++
> crypto/chacha20_generic.c | 137 -
> crypto/chacha20poly1305.c | 10 +-
> crypto/chacha_generic.c | 217 ++
> crypto/nhpoly1305.c | 254 ++
> crypto/poly1305_generic.c | 174 +-
> crypto/tcrypt.c | 12 +
> crypto/testmgr.c | 30 +
> crypto/testmgr.h | 2856 ++++++++++++++++-
> drivers/char/random.c | 51 +-
> drivers/crypto/caam/caamalg.c | 2 +-
> drivers/crypto/caam/caamalg_qi2.c | 8 +-
> drivers/crypto/caam/compat.h | 2 +-
> include/crypto/chacha.h | 54 +
> include/crypto/chacha20.h | 28 -
> include/crypto/nhpoly1305.h | 74 +
> include/crypto/poly1305.h | 28 +-
> lib/Makefile | 2 +-
> lib/{chacha20.c => chacha.c} | 59 +-
> 31 files changed, 4931 insertions(+), 515 deletions(-)
> rename arch/arm/crypto/{chacha20-neon-core.S => chacha-neon-core.S} (90%)
> create mode 100644 arch/arm/crypto/chacha-neon-glue.c
> delete mode 100644 arch/arm/crypto/chacha20-neon-glue.c
> create mode 100644 arch/arm/crypto/nh-neon-core.S
> create mode 100644 arch/arm/crypto/nhpoly1305-neon-glue.c
> create mode 100644 crypto/adiantum.c
> delete mode 100644 crypto/chacha20_generic.c
> create mode 100644 crypto/chacha_generic.c
> create mode 100644 crypto/nhpoly1305.c
> create mode 100644 include/crypto/chacha.h
> delete mode 100644 include/crypto/chacha20.h
> create mode 100644 include/crypto/nhpoly1305.h
> rename lib/{chacha20.c => chacha.c} (58%)
All applied. Thanks.
--
Email: Herbert Xu <herbert@...dor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt
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