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| author | Eric Biggers <ebiggers@google.com> | 2019-06-20 21:15:05 +0300 |
|---|---|---|
| committer | Eric Biggers <ebiggers@google.com> | 2019-06-27 20:29:33 +0300 |
| commit | adbd9b4dee70c36eaa30ce93ffcd968533044efc (patch) | |
| tree | b8b36e39ba4b6cd44fc490efe373f17190cc9caf /Documentation/filesystems/fscrypt.rst | |
| parent | 0bb06cac060dd033153277a0d9dab9fd8aa455a2 (diff) | |
| download | linux-adbd9b4dee70c36eaa30ce93ffcd968533044efc.tar.xz | |
fscrypt: remove selection of CONFIG_CRYPTO_SHA256
fscrypt only uses SHA-256 for AES-128-CBC-ESSIV, which isn't the default
and is only recommended on platforms that have hardware accelerated
AES-CBC but not AES-XTS. There's no link-time dependency, since SHA-256
is requested via the crypto API on first use.
To reduce bloat, we should limit FS_ENCRYPTION to selecting the default
algorithms only. SHA-256 by itself isn't that much bloat, but it's
being discussed to move ESSIV into a crypto API template, which would
incidentally bring in other things like "authenc" support, which would
all end up being built-in since FS_ENCRYPTION is now a bool.
For Adiantum encryption we already just document that users who want to
use it have to enable CONFIG_CRYPTO_ADIANTUM themselves. So, let's do
the same for AES-128-CBC-ESSIV and CONFIG_CRYPTO_SHA256.
Acked-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Eric Biggers <ebiggers@google.com>
Diffstat (limited to 'Documentation/filesystems/fscrypt.rst')
| -rw-r--r-- | Documentation/filesystems/fscrypt.rst | 4 |
1 files changed, 3 insertions, 1 deletions
diff --git a/Documentation/filesystems/fscrypt.rst b/Documentation/filesystems/fscrypt.rst index 08c23b60e016..87d4e266ffc8 100644 --- a/Documentation/filesystems/fscrypt.rst +++ b/Documentation/filesystems/fscrypt.rst @@ -191,7 +191,9 @@ Currently, the following pairs of encryption modes are supported: If unsure, you should use the (AES-256-XTS, AES-256-CTS-CBC) pair. AES-128-CBC was added only for low-powered embedded devices with -crypto accelerators such as CAAM or CESA that do not support XTS. +crypto accelerators such as CAAM or CESA that do not support XTS. To +use AES-128-CBC, CONFIG_CRYPTO_SHA256 (or another SHA-256 +implementation) must be enabled so that ESSIV can be used. Adiantum is a (primarily) stream cipher-based mode that is fast even on CPUs without dedicated crypto instructions. It's also a true |