diff options
| author | Daniel Walter <dwalter@sigma-star.at> | 2017-06-19 09:27:58 +0200 |
|---|---|---|
| committer | Theodore Ts'o <tytso@mit.edu> | 2017-06-23 20:05:07 -0400 |
| commit | b7e7cf7a66a27e62c5f873a0068cee34094bf5d7 (patch) | |
| tree | e86d2bbc849e8a854e7f3a22846a08bef49423b9 /include/linux/fscrypt_common.h | |
| parent | 27e47a6342e21b005a15a1f0afea0b6f179e0a71 (diff) | |
fscrypt: add support for AES-128-CBC
fscrypt provides facilities to use different encryption algorithms which
are selectable by userspace when setting the encryption policy. Currently,
only AES-256-XTS for file contents and AES-256-CBC-CTS for file names are
implemented. This is a clear case of kernel offers the mechanism and
userspace selects a policy. Similar to what dm-crypt and ecryptfs have.
This patch adds support for using AES-128-CBC for file contents and
AES-128-CBC-CTS for file name encryption. To mitigate watermarking
attacks, IVs are generated using the ESSIV algorithm. While AES-CBC is
actually slightly less secure than AES-XTS from a security point of view,
there is more widespread hardware support. Using AES-CBC gives us the
acceptable performance while still providing a moderate level of security
for persistent storage.
Especially low-powered embedded devices with crypto accelerators such as
CAAM or CESA often only support AES-CBC. Since using AES-CBC over AES-XTS
is basically thought of a last resort, we use AES-128-CBC over AES-256-CBC
since it has less encryption rounds and yields noticeable better
performance starting from a file size of just a few kB.
Signed-off-by: Daniel Walter <dwalter@sigma-star.at>
[david@sigma-star.at: addressed review comments]
Signed-off-by: David Gstir <david@sigma-star.at>
Reviewed-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Diffstat (limited to 'include/linux/fscrypt_common.h')
| -rw-r--r-- | include/linux/fscrypt_common.h | 16 |
1 files changed, 10 insertions, 6 deletions
diff --git a/include/linux/fscrypt_common.h b/include/linux/fscrypt_common.h index 0a30c106c1e5..4022c61f7e9b 100644 --- a/include/linux/fscrypt_common.h +++ b/include/linux/fscrypt_common.h @@ -91,14 +91,18 @@ static inline bool fscrypt_dummy_context_enabled(struct inode *inode) return false; } -static inline bool fscrypt_valid_contents_enc_mode(u32 mode) +static inline bool fscrypt_valid_enc_modes(u32 contents_mode, + u32 filenames_mode) { - return (mode == FS_ENCRYPTION_MODE_AES_256_XTS); -} + if (contents_mode == FS_ENCRYPTION_MODE_AES_128_CBC && + filenames_mode == FS_ENCRYPTION_MODE_AES_128_CTS) + return true; -static inline bool fscrypt_valid_filenames_enc_mode(u32 mode) -{ - return (mode == FS_ENCRYPTION_MODE_AES_256_CTS); + if (contents_mode == FS_ENCRYPTION_MODE_AES_256_XTS && + filenames_mode == FS_ENCRYPTION_MODE_AES_256_CTS) + return true; + + return false; } static inline bool fscrypt_is_dot_dotdot(const struct qstr *str) |