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authorEric Biggers <ebiggers@google.com>2019-06-20 21:15:05 +0300
committerEric Biggers <ebiggers@google.com>2019-06-27 20:29:33 +0300
commitadbd9b4dee70c36eaa30ce93ffcd968533044efc (patch)
treeb8b36e39ba4b6cd44fc490efe373f17190cc9caf /Documentation/filesystems/fscrypt.rst
parent0bb06cac060dd033153277a0d9dab9fd8aa455a2 (diff)
downloadlinux-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.rst4
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