diff options
| author | Eric Biggers <ebiggers@google.com> | 2019-01-06 08:36:21 -0500 |
|---|---|---|
| committer | Theodore Ts'o <tytso@mit.edu> | 2019-01-06 08:36:21 -0500 |
| commit | 8094c3ceb21ad93896fd4d238e8ba41911932eaf (patch) | |
| tree | 8dcc0b7473ad0996841ce20dc84febfe45b7e591 /include | |
| parent | 7beb01f74415c56f5992922b5b902b45d365e694 (diff) | |
fscrypt: add Adiantum support
Add support for the Adiantum encryption mode to fscrypt. Adiantum is a
tweakable, length-preserving encryption mode with security provably
reducible to that of XChaCha12 and AES-256, subject to a security bound.
It's also a true wide-block mode, unlike XTS. See the paper
"Adiantum: length-preserving encryption for entry-level processors"
(https://eprint.iacr.org/2018/720.pdf) for more details. Also see
commit 059c2a4d8e16 ("crypto: adiantum - add Adiantum support").
On sufficiently long messages, Adiantum's bottlenecks are XChaCha12 and
the NH hash function. These algorithms are fast even on processors
without dedicated crypto instructions. Adiantum makes it feasible to
enable storage encryption on low-end mobile devices that lack AES
instructions; currently such devices are unencrypted. On ARM Cortex-A7,
on 4096-byte messages Adiantum encryption is about 4 times faster than
AES-256-XTS encryption; decryption is about 5 times faster.
In fscrypt, Adiantum is suitable for encrypting both file contents and
names. With filenames, it fixes a known weakness: when two filenames in
a directory share a common prefix of >= 16 bytes, with CTS-CBC their
encrypted filenames share a common prefix too, leaking information.
Adiantum does not have this problem.
Since Adiantum also accepts long tweaks (IVs), it's also safe to use the
master key directly for Adiantum encryption rather than deriving
per-file keys, provided that the per-file nonce is included in the IVs
and the master key isn't used for any other encryption mode. This
configuration saves memory and improves performance. A new fscrypt
policy flag is added to allow users to opt-in to this configuration.
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Diffstat (limited to 'include')
| -rw-r--r-- | include/uapi/linux/fs.h | 4 |
1 files changed, 3 insertions, 1 deletions
diff --git a/include/uapi/linux/fs.h b/include/uapi/linux/fs.h index a441ea1bfe6d..086e7ee550df 100644 --- a/include/uapi/linux/fs.h +++ b/include/uapi/linux/fs.h @@ -269,7 +269,8 @@ struct fsxattr { #define FS_POLICY_FLAGS_PAD_16 0x02 #define FS_POLICY_FLAGS_PAD_32 0x03 #define FS_POLICY_FLAGS_PAD_MASK 0x03 -#define FS_POLICY_FLAGS_VALID 0x03 +#define FS_POLICY_FLAG_DIRECT_KEY 0x04 /* use master key directly */ +#define FS_POLICY_FLAGS_VALID 0x07 /* Encryption algorithms */ #define FS_ENCRYPTION_MODE_INVALID 0 @@ -281,6 +282,7 @@ struct fsxattr { #define FS_ENCRYPTION_MODE_AES_128_CTS 6 #define FS_ENCRYPTION_MODE_SPECK128_256_XTS 7 /* Removed, do not use. */ #define FS_ENCRYPTION_MODE_SPECK128_256_CTS 8 /* Removed, do not use. */ +#define FS_ENCRYPTION_MODE_ADIANTUM 9 struct fscrypt_policy { __u8 version; |