Lines Matching full:encryption
2 Filesystem-level encryption (fscrypt)
9 transparent encryption of files and directories.
15 use encryption, see the documentation for the userspace tool `fscrypt
20 <https://source.android.com/security/encryption/file-based>`_, over
56 Provided that userspace chooses a strong encryption key, fscrypt
72 fscrypt (and storage encryption in general) can only provide limited
80 Cryptographic API algorithms or inline encryption hardware are. If a
89 After an encryption key has been added, fscrypt does not hide the
97 encryption but rather only by the correctness of the kernel.
98 Therefore, any encryption-specific access control checks would merely
107 security vulnerability, can compromise all encryption keys that are
110 However, fscrypt allows encryption keys to be removed from the kernel,
115 encryption key from kernel memory. If it does so, it will also try to
151 v1 encryption policies have some weaknesses with respect to online
165 - Non-root users cannot securely remove encryption keys.
167 All the above problems are fixed with v2 encryption policies. For
168 this reason among others, it is recommended to use v2 encryption
180 encryption modes being used. For example, if any AES-256 mode is
182 stricter requirement applies if the key is used by a v1 encryption
208 encryption directly. Instead, they are only used as input to a KDF
212 the key is used for v1 encryption policies or for v2 encryption
214 encryption policies. (No real-world attack is currently known on this
218 For v1 encryption policies, the KDF only supports deriving per-file
219 encryption keys. It works by encrypting the master key with
224 For v2 encryption policies, the KDF is HKDF-SHA512. The master key is
227 key to be derived. For example, when a per-file encryption key is
237 Per-file encryption keys
241 "tweak" the encryption of each file so that the same plaintext in two
246 inode's encryption xattr. Then, it uses a KDF (as described in `Key
262 The Adiantum encryption mode (see `Encryption modes and usage`_) is
263 suitable for both contents and filenames encryption, and it accepts
271 per-file encryption keys are not used. Instead, whenever any data
275 - For v1 encryption policies, the encryption is done directly with the
279 - For v2 encryption policies, the encryption is done with a per-mode
281 other v2 encryption policies.
287 the encryption keys are derived from the master key, encryption mode
289 protected by the same master key sharing a single contents encryption
290 key and a single filenames encryption key. To still encrypt different
294 This format is optimized for use with inline encryption hardware
306 This format is optimized for use with inline encryption hardware
315 For master keys used for v2 encryption policies, a unique 16-byte "key
325 just like deriving a per-file encryption key, except that a different
329 Encryption modes and usage
332 fscrypt allows one encryption mode to be specified for file contents
333 and one encryption mode to be specified for filenames. Different
334 directory trees are permitted to use different encryption modes.
339 Currently, the following pairs of encryption modes are supported:
350 Authenticated encryption modes are not currently supported because of
352 contents encryption uses a block cipher in `XTS mode
356 or a wide-block cipher. Filenames encryption uses a
366 upgrades the filenames encryption to use a wide-block cipher. (A
369 entire result.) As described in `Filenames encryption`_, a wide-block
399 and AES-256-CBC-CTS encryption. For optimal performance, it is
402 wish to use. Support for any "non-default" encryption modes typically
405 Below, some relevant options are listed by encryption mode. Note,
407 platform; refer to the kconfig menus. File contents encryption can
408 also be configured to use inline encryption hardware instead of the
409 kernel crypto API (see `Inline encryption support`_); in that case,
454 Contents encryption
457 For contents encryption, each file's contents is divided into "data
463 Note: the encryption depending on the offset into the file means that
474 the encryption policy; see `FS_IOC_SET_ENCRYPTION_POLICY`_.
481 In the case of compression + encryption, the compressed data is
488 As mentioned in `Key hierarchy`_, the default encryption setting uses
491 encryption setting that does not use per-file keys. For these, some
512 key is the SHA-256 hash of the file's contents encryption key.
514 Filenames encryption
531 wide-block encryption modes.
533 All supported filenames encryption modes accept any plaintext length
551 Setting an encryption policy
557 The FS_IOC_SET_ENCRYPTION_POLICY ioctl sets an encryption policy on an
559 has the specified encryption policy. It takes in a pointer to
596 encryption modes to use. If unsure, use FSCRYPT_MODE_AES_256_XTS
598 (4) for ``filenames_encryption_mode``. For details, see `Encryption
601 v1 encryption policies only support three combinations of modes:
618 v1 encryption policies only support the PAD_* and DIRECT_KEY flags.
619 The other flags are only supported by v2 encryption policies.
626 the granularity of file contents encryption. For example, setting
628 underlying encryption algorithm (such as AES-256-XTS) in 4096-byte
639 compatibility with inline encryption hardware that only supports
642 particular system's inline encryption hardware.
647 - For v2 encryption policies, ``__reserved`` must be zeroed.
649 - For v1 encryption policies, ``master_key_descriptor`` specifies how
658 For v2 encryption policies, ``master_key_descriptor`` has been
668 encryption policy is assigned to the directory, turning it into an
672 directory will be encrypted, inheriting the same encryption policy.
676 FS_IOC_SET_ENCRYPTION_POLICY validates that the specified encryption
681 When a v2 encryption policy is assigned to a directory, it is also
699 - ``EEXIST``: the file is already encrypted with an encryption policy
701 - ``EINVAL``: an invalid encryption policy was specified (invalid
703 encryption policy was specified but the directory has the casefold
705 - ``ENOKEY``: a v2 encryption policy was specified, but the key with
712 - ``ENOTTY``: this type of filesystem does not implement encryption
713 - ``EOPNOTSUPP``: the kernel was not configured with encryption
715 had encryption enabled on it. (For example, to use encryption on an
724 Getting an encryption policy
727 Two ioctls are available to get a file's encryption policy:
741 The FS_IOC_GET_ENCRYPTION_POLICY_EX ioctl retrieves the encryption
767 encryption policy version
769 - ``ENOTTY``: this type of filesystem does not implement encryption,
772 - ``EOPNOTSUPP``: the kernel was not configured with encryption
774 had encryption enabled on it
776 encryption policy version, but the policy struct does not fit into
788 encryption policy, if any, for a directory or regular file. However,
797 encrypted using a newer encryption policy version.
805 value is intended to used as a salt when deriving an encryption key
811 Getting a file's encryption nonce
819 encryption is being done correctly. It is not needed for normal use
828 The FS_IOC_ADD_ENCRYPTION_KEY ioctl adds a master encryption key to
865 - If the key is being added for use by v1 encryption policies, then
873 Alternatively, if the key is being added for use by v2 encryption
935 - ``ENOTTY``: this type of filesystem does not implement encryption
936 - ``EOPNOTSUPP``: the kernel was not configured with encryption
938 had encryption enabled on it
943 For v1 encryption policies, a master encryption key can also be
948 This method is deprecated (and not supported for v2 encryption
966 ``master_key_descriptor`` that was set in the encryption policy. The
1009 encryption key from the filesystem, and possibly removes the key
1027 - To remove a key used by v1 encryption policies, set
1033 - To remove a key used by v2 encryption policies, set
1080 - ``ENOTTY``: this type of filesystem does not implement encryption
1081 - ``EOPNOTSUPP``: the kernel was not configured with encryption
1083 had encryption enabled on it
1106 master encryption key. It can be executed on any file or directory on
1129 - To get the status of a key for v1 encryption policies, set
1133 - To get the status of a key for v2 encryption policies, set
1158 - ``ENOTTY``: this type of filesystem does not implement encryption
1159 - ``EOPNOTSUPP``: the kernel was not configured with encryption
1161 had encryption enabled on it
1172 encryption policies using the legacy mechanism involving
1181 With the encryption key, encrypted regular files, directories, and
1183 after all, the encryption is intended to be transparent. However,
1186 - Unencrypted files, or files encrypted with a different encryption
1188 linked into an encrypted directory; see `Encryption policy
1230 files, directories, and symlinks even before their encryption key has
1231 been added, or after their encryption key has been removed:
1267 without the encryption key. This would require special APIs which
1270 Encryption policy enforcement
1273 After an encryption policy has been set on a directory, all regular
1275 (recursively) will inherit that encryption policy. Special files ---
1280 files, or files encrypted with a different encryption policy, in an
1284 attacks that try to disable or downgrade encryption in known locations
1287 this by validating all top-level encryption policies prior to access.
1289 Inline encryption support
1302 encryption hardware* that can encrypt/decrypt data while it is on its
1303 way to/from the storage device. Linux supports inline encryption
1305 blk-crypto allows filesystems to attach encryption contexts to bios
1308 :ref:`Documentation/block/inline-encryption.rst <inline_encryption>`.
1317 encryption when possible; it doesn't force its use. fscrypt will
1319 inline encryption hardware doesn't have the needed crypto capabilities
1320 (e.g. support for the needed encryption algorithm and data unit size)
1327 inline encryption hardware that supports that data unit size.
1329 Inline encryption doesn't affect the ciphertext or other aspects of
1340 * The file must be using inline encryption. Usually this means that
1342 encryption hardware must be present. However, a software fallback
1343 is also available. For details, see `Inline encryption support`_.
1357 Encryption context
1360 An encryption policy is represented on-disk by
1365 setxattr() because of the special semantics of the encryption xattr.
1366 (In particular, there would be much confusion if an encryption policy
1395 policy structs (see `Setting an encryption policy`_), except that the
1398 different files to be encrypted differently; see `Per-file encryption
1404 When inline encryption is used, filesystems just need to associate
1405 encryption contexts with bios to specify how the block layer or the
1406 inline encryption hardware will encrypt/decrypt the file contents.
1408 When inline encryption isn't used, filesystems must encrypt/decrypt
1421 buffers regardless of encryption. Other filesystems, such as ext4 and
1422 F2FS, have to allocate bounce pages specially for encryption.
1433 With encryption, lookups must be supported and efficient both with and
1434 without the encryption key. Clearly, it would not work to hash the
1472 inline encryption support. For example, to test ext4 and
1473 f2fs encryption using `kvm-xfstests
1479 UBIFS encryption can also be tested this way, but it should be done in
1485 No tests should fail. However, tests that use non-default encryption