mirror of
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git
synced 2024-08-23 09:19:51 +00:00
![Masanari Iida](/assets/img/avatar_default.png)
Signed-off-by: Masanari Iida <standby24x7@gmail.com> Acked-by: Randy Dunlap <rdunlap@xenotime.net> Signed-off-by: Jiri Kosina <jkosina@suse.cz>
160 lines
7.4 KiB
Text
160 lines
7.4 KiB
Text
Trusted and Encrypted Keys
|
|
|
|
Trusted and Encrypted Keys are two new key types added to the existing kernel
|
|
key ring service. Both of these new types are variable length symmetric keys,
|
|
and in both cases all keys are created in the kernel, and user space sees,
|
|
stores, and loads only encrypted blobs. Trusted Keys require the availability
|
|
of a Trusted Platform Module (TPM) chip for greater security, while Encrypted
|
|
Keys can be used on any system. All user level blobs, are displayed and loaded
|
|
in hex ascii for convenience, and are integrity verified.
|
|
|
|
Trusted Keys use a TPM both to generate and to seal the keys. Keys are sealed
|
|
under a 2048 bit RSA key in the TPM, and optionally sealed to specified PCR
|
|
(integrity measurement) values, and only unsealed by the TPM, if PCRs and blob
|
|
integrity verifications match. A loaded Trusted Key can be updated with new
|
|
(future) PCR values, so keys are easily migrated to new pcr values, such as
|
|
when the kernel and initramfs are updated. The same key can have many saved
|
|
blobs under different PCR values, so multiple boots are easily supported.
|
|
|
|
By default, trusted keys are sealed under the SRK, which has the default
|
|
authorization value (20 zeros). This can be set at takeownership time with the
|
|
trouser's utility: "tpm_takeownership -u -z".
|
|
|
|
Usage:
|
|
keyctl add trusted name "new keylen [options]" ring
|
|
keyctl add trusted name "load hex_blob [pcrlock=pcrnum]" ring
|
|
keyctl update key "update [options]"
|
|
keyctl print keyid
|
|
|
|
options:
|
|
keyhandle= ascii hex value of sealing key default 0x40000000 (SRK)
|
|
keyauth= ascii hex auth for sealing key default 0x00...i
|
|
(40 ascii zeros)
|
|
blobauth= ascii hex auth for sealed data default 0x00...
|
|
(40 ascii zeros)
|
|
blobauth= ascii hex auth for sealed data default 0x00...
|
|
(40 ascii zeros)
|
|
pcrinfo= ascii hex of PCR_INFO or PCR_INFO_LONG (no default)
|
|
pcrlock= pcr number to be extended to "lock" blob
|
|
migratable= 0|1 indicating permission to reseal to new PCR values,
|
|
default 1 (resealing allowed)
|
|
|
|
"keyctl print" returns an ascii hex copy of the sealed key, which is in standard
|
|
TPM_STORED_DATA format. The key length for new keys are always in bytes.
|
|
Trusted Keys can be 32 - 128 bytes (256 - 1024 bits), the upper limit is to fit
|
|
within the 2048 bit SRK (RSA) keylength, with all necessary structure/padding.
|
|
|
|
Encrypted keys do not depend on a TPM, and are faster, as they use AES for
|
|
encryption/decryption. New keys are created from kernel generated random
|
|
numbers, and are encrypted/decrypted using a specified 'master' key. The
|
|
'master' key can either be a trusted-key or user-key type. The main
|
|
disadvantage of encrypted keys is that if they are not rooted in a trusted key,
|
|
they are only as secure as the user key encrypting them. The master user key
|
|
should therefore be loaded in as secure a way as possible, preferably early in
|
|
boot.
|
|
|
|
The decrypted portion of encrypted keys can contain either a simple symmetric
|
|
key or a more complex structure. The format of the more complex structure is
|
|
application specific, which is identified by 'format'.
|
|
|
|
Usage:
|
|
keyctl add encrypted name "new [format] key-type:master-key-name keylen"
|
|
ring
|
|
keyctl add encrypted name "load hex_blob" ring
|
|
keyctl update keyid "update key-type:master-key-name"
|
|
|
|
format:= 'default | ecryptfs'
|
|
key-type:= 'trusted' | 'user'
|
|
|
|
|
|
Examples of trusted and encrypted key usage:
|
|
|
|
Create and save a trusted key named "kmk" of length 32 bytes:
|
|
|
|
$ keyctl add trusted kmk "new 32" @u
|
|
440502848
|
|
|
|
$ keyctl show
|
|
Session Keyring
|
|
-3 --alswrv 500 500 keyring: _ses
|
|
97833714 --alswrv 500 -1 \_ keyring: _uid.500
|
|
440502848 --alswrv 500 500 \_ trusted: kmk
|
|
|
|
$ keyctl print 440502848
|
|
0101000000000000000001005d01b7e3f4a6be5709930f3b70a743cbb42e0cc95e18e915
|
|
3f60da455bbf1144ad12e4f92b452f966929f6105fd29ca28e4d4d5a031d068478bacb0b
|
|
27351119f822911b0a11ba3d3498ba6a32e50dac7f32894dd890eb9ad578e4e292c83722
|
|
a52e56a097e6a68b3f56f7a52ece0cdccba1eb62cad7d817f6dc58898b3ac15f36026fec
|
|
d568bd4a706cb60bb37be6d8f1240661199d640b66fb0fe3b079f97f450b9ef9c22c6d5d
|
|
dd379f0facd1cd020281dfa3c70ba21a3fa6fc2471dc6d13ecf8298b946f65345faa5ef0
|
|
f1f8fff03ad0acb083725535636addb08d73dedb9832da198081e5deae84bfaf0409c22b
|
|
e4a8aea2b607ec96931e6f4d4fe563ba
|
|
|
|
$ keyctl pipe 440502848 > kmk.blob
|
|
|
|
Load a trusted key from the saved blob:
|
|
|
|
$ keyctl add trusted kmk "load `cat kmk.blob`" @u
|
|
268728824
|
|
|
|
$ keyctl print 268728824
|
|
0101000000000000000001005d01b7e3f4a6be5709930f3b70a743cbb42e0cc95e18e915
|
|
3f60da455bbf1144ad12e4f92b452f966929f6105fd29ca28e4d4d5a031d068478bacb0b
|
|
27351119f822911b0a11ba3d3498ba6a32e50dac7f32894dd890eb9ad578e4e292c83722
|
|
a52e56a097e6a68b3f56f7a52ece0cdccba1eb62cad7d817f6dc58898b3ac15f36026fec
|
|
d568bd4a706cb60bb37be6d8f1240661199d640b66fb0fe3b079f97f450b9ef9c22c6d5d
|
|
dd379f0facd1cd020281dfa3c70ba21a3fa6fc2471dc6d13ecf8298b946f65345faa5ef0
|
|
f1f8fff03ad0acb083725535636addb08d73dedb9832da198081e5deae84bfaf0409c22b
|
|
e4a8aea2b607ec96931e6f4d4fe563ba
|
|
|
|
Reseal a trusted key under new pcr values:
|
|
|
|
$ keyctl update 268728824 "update pcrinfo=`cat pcr.blob`"
|
|
$ keyctl print 268728824
|
|
010100000000002c0002800093c35a09b70fff26e7a98ae786c641e678ec6ffb6b46d805
|
|
77c8a6377aed9d3219c6dfec4b23ffe3000001005d37d472ac8a44023fbb3d18583a4f73
|
|
d3a076c0858f6f1dcaa39ea0f119911ff03f5406df4f7f27f41da8d7194f45c9f4e00f2e
|
|
df449f266253aa3f52e55c53de147773e00f0f9aca86c64d94c95382265968c354c5eab4
|
|
9638c5ae99c89de1e0997242edfb0b501744e11ff9762dfd951cffd93227cc513384e7e6
|
|
e782c29435c7ec2edafaa2f4c1fe6e7a781b59549ff5296371b42133777dcc5b8b971610
|
|
94bc67ede19e43ddb9dc2baacad374a36feaf0314d700af0a65c164b7082401740e489c9
|
|
7ef6a24defe4846104209bf0c3eced7fa1a672ed5b125fc9d8cd88b476a658a4434644ef
|
|
df8ae9a178e9f83ba9f08d10fa47e4226b98b0702f06b3b8
|
|
|
|
The initial consumer of trusted keys is EVM, which at boot time needs a high
|
|
quality symmetric key for HMAC protection of file metadata. The use of a
|
|
trusted key provides strong guarantees that the EVM key has not been
|
|
compromised by a user level problem, and when sealed to specific boot PCR
|
|
values, protects against boot and offline attacks. Create and save an
|
|
encrypted key "evm" using the above trusted key "kmk":
|
|
|
|
option 1: omitting 'format'
|
|
$ keyctl add encrypted evm "new trusted:kmk 32" @u
|
|
159771175
|
|
|
|
option 2: explicitly defining 'format' as 'default'
|
|
$ keyctl add encrypted evm "new default trusted:kmk 32" @u
|
|
159771175
|
|
|
|
$ keyctl print 159771175
|
|
default trusted:kmk 32 2375725ad57798846a9bbd240de8906f006e66c03af53b1b3
|
|
82dbbc55be2a44616e4959430436dc4f2a7a9659aa60bb4652aeb2120f149ed197c564e0
|
|
24717c64 5972dcb82ab2dde83376d82b2e3c09ffc
|
|
|
|
$ keyctl pipe 159771175 > evm.blob
|
|
|
|
Load an encrypted key "evm" from saved blob:
|
|
|
|
$ keyctl add encrypted evm "load `cat evm.blob`" @u
|
|
831684262
|
|
|
|
$ keyctl print 831684262
|
|
default trusted:kmk 32 2375725ad57798846a9bbd240de8906f006e66c03af53b1b3
|
|
82dbbc55be2a44616e4959430436dc4f2a7a9659aa60bb4652aeb2120f149ed197c564e0
|
|
24717c64 5972dcb82ab2dde83376d82b2e3c09ffc
|
|
|
|
Other uses for trusted and encrypted keys, such as for disk and file encryption
|
|
are anticipated. In particular the new format 'ecryptfs' has been defined in
|
|
in order to use encrypted keys to mount an eCryptfs filesystem. More details
|
|
about the usage can be found in the file
|
|
'Documentation/security/keys-ecryptfs.txt'.
|