From b7e7cf7a66a27e62c5f873a0068cee34094bf5d7 Mon Sep 17 00:00:00 2001 From: Daniel Walter Date: Mon, 19 Jun 2017 09:27:58 +0200 Subject: 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 [david@sigma-star.at: addressed review comments] Signed-off-by: David Gstir Reviewed-by: Eric Biggers Signed-off-by: Theodore Ts'o --- include/uapi/linux/fs.h | 2 ++ 1 file changed, 2 insertions(+) (limited to 'include/uapi/linux/fs.h') diff --git a/include/uapi/linux/fs.h b/include/uapi/linux/fs.h index 24e61a54feaa..a2a3ffb06038 100644 --- a/include/uapi/linux/fs.h +++ b/include/uapi/linux/fs.h @@ -272,6 +272,8 @@ struct fsxattr { #define FS_ENCRYPTION_MODE_AES_256_GCM 2 #define FS_ENCRYPTION_MODE_AES_256_CBC 3 #define FS_ENCRYPTION_MODE_AES_256_CTS 4 +#define FS_ENCRYPTION_MODE_AES_128_CBC 5 +#define FS_ENCRYPTION_MODE_AES_128_CTS 6 struct fscrypt_policy { __u8 version; -- cgit v1.2.3-55-g7522