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>
diff --git a/fs/crypto/fscrypt_private.h b/fs/crypto/fscrypt_private.h
index 1e1f8a3..a1d5021 100644
--- a/fs/crypto/fscrypt_private.h
+++ b/fs/crypto/fscrypt_private.h
@@ -12,10 +12,13 @@
#define _FSCRYPT_PRIVATE_H
#include <linux/fscrypt_supp.h>
+#include <crypto/hash.h>
/* Encryption parameters */
-#define FS_XTS_TWEAK_SIZE 16
+#define FS_IV_SIZE 16
#define FS_AES_128_ECB_KEY_SIZE 16
+#define FS_AES_128_CBC_KEY_SIZE 16
+#define FS_AES_128_CTS_KEY_SIZE 16
#define FS_AES_256_GCM_KEY_SIZE 32
#define FS_AES_256_CBC_KEY_SIZE 32
#define FS_AES_256_CTS_KEY_SIZE 32
@@ -54,6 +57,7 @@ struct fscrypt_info {
u8 ci_filename_mode;
u8 ci_flags;
struct crypto_skcipher *ci_ctfm;
+ struct crypto_cipher *ci_essiv_tfm;
u8 ci_master_key[FS_KEY_DESCRIPTOR_SIZE];
};
@@ -87,4 +91,7 @@ extern int fscrypt_do_page_crypto(const struct inode *inode,
extern struct page *fscrypt_alloc_bounce_page(struct fscrypt_ctx *ctx,
gfp_t gfp_flags);
+/* keyinfo.c */
+extern void __exit fscrypt_essiv_cleanup(void);
+
#endif /* _FSCRYPT_PRIVATE_H */
