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-rw-r--r--Documentation/filesystems/fscrypt.rst6
1 files changed, 6 insertions, 0 deletions
diff --git a/Documentation/filesystems/fscrypt.rst b/Documentation/filesystems/fscrypt.rst
index c0784ec05553..ef183387da20 100644
--- a/Documentation/filesystems/fscrypt.rst
+++ b/Documentation/filesystems/fscrypt.rst
@@ -370,6 +370,12 @@ CONFIG_CRYPTO_HCTR2 must be enabled. Also, fast implementations of XCTR and
POLYVAL should be enabled, e.g. CRYPTO_POLYVAL_ARM64_CE and
CRYPTO_AES_ARM64_CE_BLK for ARM64.
+SM4 is a Chinese block cipher that is an alternative to AES. It has
+not seen as much security review as AES, and it only has a 128-bit key
+size. It may be useful in cases where its use is mandated.
+Otherwise, it should not be used. For SM4 support to be available, it
+also needs to be enabled in the kernel crypto API.
+
New encryption modes can be added relatively easily, without changes
to individual filesystems. However, authenticated encryption (AE)
modes are not currently supported because of the difficulty of dealing