lkml.org 
[lkml]   [2018]   [Nov]   [6]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    From
    Subject[RFC PATCH v3 00/15] crypto: Adiantum support
    Date
    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.

    Patch 15 adds Adiantum support to fscrypt ("file-based encryption").
    In fscrypt, Adiantum is used for filenames encryption as well as
    contents encryption; since Adiantum is a SPRP, it fixes the information
    leak when filenames share a common prefix. We also take advantage of
    Adiantum's support for long tweaks to include the per-inode nonce
    directly in the tweak, which allows providing an option to skip the
    per-file key derivation, providing even greater performance benefits.

    This patchset applies to v4.20-rc1. It can also be found in git at
    branch "adiantum-v3" of:
    https://git.kernel.org/pub/scm/linux/kernel/git/ebiggers/linux.git

    As before, the XChaCha and Poly1305 changes conflict with the new "Zinc"
    crypto library. But I don't know when Zinc will be merged, so for now
    I've continued to base this patchset on upstream. An experimental
    version of this patchset based on Zinc can be found at branch
    "adiantum-zinc" of the git repository above.

    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 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 (15):
    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
    fscrypt: add Adiantum support

    Documentation/filesystems/fscrypt.rst | 187 +-
    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 | 52 +-
    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 +-
    fs/crypto/crypto.c | 35 +-
    fs/crypto/fname.c | 22 +-
    fs/crypto/fscrypt_private.h | 66 +-
    fs/crypto/keyinfo.c | 322 +-
    fs/crypto/policy.c | 5 +-
    include/crypto/chacha.h | 53 +
    include/crypto/chacha20.h | 27 -
    include/crypto/nhpoly1305.h | 74 +
    include/crypto/poly1305.h | 28 +-
    include/uapi/linux/fs.h | 4 +-
    lib/Makefile | 2 +-
    lib/{chacha20.c => chacha.c} | 59 +-
    35 files changed, 5380 insertions(+), 697 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%)

    --
    2.19.1.930.g4563a0d9d0-goog

    \
     
     \ /
      Last update: 2018-11-06 00:29    [W:4.056 / U:0.020 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site