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Diffstat (limited to 'Documentation/filesystems/fscrypt.rst')
| -rw-r--r-- | Documentation/filesystems/fscrypt.rst | 45 |
1 files changed, 15 insertions, 30 deletions
diff --git a/Documentation/filesystems/fscrypt.rst b/Documentation/filesystems/fscrypt.rst index 29e84d125e02..696a5844bfa3 100644 --- a/Documentation/filesystems/fscrypt.rst +++ b/Documentation/filesystems/fscrypt.rst @@ -147,9 +147,8 @@ However, these ioctls have some limitations: were wiped. To partially solve this, you can add init_on_free=1 to your kernel command line. However, this has a performance cost. -- Secret keys might still exist in CPU registers, in crypto - accelerator hardware (if used by the crypto API to implement any of - the algorithms), or in other places not explicitly considered here. +- Secret keys might still exist in CPU registers or in other places + not explicitly considered here. Full system compromise ~~~~~~~~~~~~~~~~~~~~~~ @@ -406,9 +405,12 @@ the work is done by XChaCha12, which is much faster than AES when AES acceleration is unavailable. For more information about Adiantum, see `the Adiantum paper <https://eprint.iacr.org/2018/720.pdf>`_. -The (AES-128-CBC-ESSIV, AES-128-CBC-CTS) pair exists only to support -systems whose only form of AES acceleration is an off-CPU crypto -accelerator such as CAAM or CESA that does not support XTS. +The (AES-128-CBC-ESSIV, AES-128-CBC-CTS) pair was added to try to +provide a more efficient option for systems that lack AES instructions +in the CPU but do have a non-inline crypto engine such as CAAM or CESA +that supports AES-CBC (and not AES-XTS). This is deprecated. It has +been shown that just doing AES on the CPU is actually faster. +Moreover, Adiantum is faster still and is recommended on such systems. The remaining mode pairs are the "national pride ciphers": @@ -468,14 +470,6 @@ API, but the filenames mode still does. - Recommended: - AES-CBC acceleration -fscrypt also uses HMAC-SHA512 for key derivation, so enabling SHA-512 -acceleration is recommended: - -- SHA-512 - - Recommended: - - arm64: CONFIG_CRYPTO_SHA512_ARM64_CE - - x86: CONFIG_CRYPTO_SHA512_SSSE3 - Contents encryption ------------------- @@ -1326,22 +1320,13 @@ this by validating all top-level encryption policies prior to access. Inline encryption support ========================= -By default, fscrypt uses the kernel crypto API for all cryptographic -operations (other than HKDF, which fscrypt partially implements -itself). The kernel crypto API supports hardware crypto accelerators, -but only ones that work in the traditional way where all inputs and -outputs (e.g. plaintexts and ciphertexts) are in memory. fscrypt can -take advantage of such hardware, but the traditional acceleration -model isn't particularly efficient and fscrypt hasn't been optimized -for it. - -Instead, many newer systems (especially mobile SoCs) have *inline -encryption hardware* that can encrypt/decrypt data while it is on its -way to/from the storage device. Linux supports inline encryption -through a set of extensions to the block layer called *blk-crypto*. -blk-crypto allows filesystems to attach encryption contexts to bios -(I/O requests) to specify how the data will be encrypted or decrypted -in-line. For more information about blk-crypto, see +Many newer systems (especially mobile SoCs) have *inline encryption +hardware* that can encrypt/decrypt data while it is on its way to/from +the storage device. Linux supports inline encryption through a set of +extensions to the block layer called *blk-crypto*. blk-crypto allows +filesystems to attach encryption contexts to bios (I/O requests) to +specify how the data will be encrypted or decrypted in-line. For more +information about blk-crypto, see :ref:`Documentation/block/inline-encryption.rst <inline_encryption>`. On supported filesystems (currently ext4 and f2fs), fscrypt can use |