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>
This commit is contained in:
Eric Biggers 2019-06-20 11:15:05 -07:00
Родитель 0bb06cac06
Коммит adbd9b4dee
2 изменённых файлов: 3 добавлений и 2 удалений

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@ -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

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@ -7,7 +7,6 @@ config FS_ENCRYPTION
select CRYPTO_ECB
select CRYPTO_XTS
select CRYPTO_CTS
select CRYPTO_SHA256
select KEYS
help
Enable encryption of files and directories. This