mirror of https://gitee.com/openkylin/linux.git
69 lines
3.1 KiB
Plaintext
69 lines
3.1 KiB
Plaintext
Encrypted keys for the eCryptfs filesystem
|
|
|
|
ECryptfs is a stacked filesystem which transparently encrypts and decrypts each
|
|
file using a randomly generated File Encryption Key (FEK).
|
|
|
|
Each FEK is in turn encrypted with a File Encryption Key Encryption Key (FEFEK)
|
|
either in kernel space or in user space with a daemon called 'ecryptfsd'. In
|
|
the former case the operation is performed directly by the kernel CryptoAPI
|
|
using a key, the FEFEK, derived from a user prompted passphrase; in the latter
|
|
the FEK is encrypted by 'ecryptfsd' with the help of external libraries in order
|
|
to support other mechanisms like public key cryptography, PKCS#11 and TPM based
|
|
operations.
|
|
|
|
The data structure defined by eCryptfs to contain information required for the
|
|
FEK decryption is called authentication token and, currently, can be stored in a
|
|
kernel key of the 'user' type, inserted in the user's session specific keyring
|
|
by the userspace utility 'mount.ecryptfs' shipped with the package
|
|
'ecryptfs-utils'.
|
|
|
|
The 'encrypted' key type has been extended with the introduction of the new
|
|
format 'ecryptfs' in order to be used in conjunction with the eCryptfs
|
|
filesystem. Encrypted keys of the newly introduced format store an
|
|
authentication token in its payload with a FEFEK randomly generated by the
|
|
kernel and protected by the parent master key.
|
|
|
|
In order to avoid known-plaintext attacks, the datablob obtained through
|
|
commands 'keyctl print' or 'keyctl pipe' does not contain the overall
|
|
authentication token, which content is well known, but only the FEFEK in
|
|
encrypted form.
|
|
|
|
The eCryptfs filesystem may really benefit from using encrypted keys in that the
|
|
required key can be securely generated by an Administrator and provided at boot
|
|
time after the unsealing of a 'trusted' key in order to perform the mount in a
|
|
controlled environment. Another advantage is that the key is not exposed to
|
|
threats of malicious software, because it is available in clear form only at
|
|
kernel level.
|
|
|
|
Usage:
|
|
keyctl add encrypted name "new ecryptfs key-type:master-key-name keylen" ring
|
|
keyctl add encrypted name "load hex_blob" ring
|
|
keyctl update keyid "update key-type:master-key-name"
|
|
|
|
name:= '<16 hexadecimal characters>'
|
|
key-type:= 'trusted' | 'user'
|
|
keylen:= 64
|
|
|
|
|
|
Example of encrypted key usage with the eCryptfs filesystem:
|
|
|
|
Create an encrypted key "1000100010001000" of length 64 bytes with format
|
|
'ecryptfs' and save it using a previously loaded user key "test":
|
|
|
|
$ keyctl add encrypted 1000100010001000 "new ecryptfs user:test 64" @u
|
|
19184530
|
|
|
|
$ keyctl print 19184530
|
|
ecryptfs user:test 64 490045d4bfe48c99f0d465fbbbb79e7500da954178e2de0697
|
|
dd85091f5450a0511219e9f7cd70dcd498038181466f78ac8d4c19504fcc72402bfc41c2
|
|
f253a41b7507ccaa4b2b03fff19a69d1cc0b16e71746473f023a95488b6edfd86f7fdd40
|
|
9d292e4bacded1258880122dd553a661
|
|
|
|
$ keyctl pipe 19184530 > ecryptfs.blob
|
|
|
|
Mount an eCryptfs filesystem using the created encrypted key "1000100010001000"
|
|
into the '/secret' directory:
|
|
|
|
$ mount -i -t ecryptfs -oecryptfs_sig=1000100010001000,\
|
|
ecryptfs_cipher=aes,ecryptfs_key_bytes=32 /secret /secret
|