Root/Documentation/keys-trusted-encrypted.txt

1            Trusted and Encrypted Keys
2
3Trusted and Encrypted Keys are two new key types added to the existing kernel
4key ring service. Both of these new types are variable length symmetic keys,
5and in both cases all keys are created in the kernel, and user space sees,
6stores, and loads only encrypted blobs. Trusted Keys require the availability
7of a Trusted Platform Module (TPM) chip for greater security, while Encrypted
8Keys can be used on any system. All user level blobs, are displayed and loaded
9in hex ascii for convenience, and are integrity verified.
10
11Trusted Keys use a TPM both to generate and to seal the keys. Keys are sealed
12under a 2048 bit RSA key in the TPM, and optionally sealed to specified PCR
13(integrity measurement) values, and only unsealed by the TPM, if PCRs and blob
14integrity verifications match. A loaded Trusted Key can be updated with new
15(future) PCR values, so keys are easily migrated to new pcr values, such as
16when the kernel and initramfs are updated. The same key can have many saved
17blobs under different PCR values, so multiple boots are easily supported.
18
19By default, trusted keys are sealed under the SRK, which has the default
20authorization value (20 zeros). This can be set at takeownership time with the
21trouser's utility: "tpm_takeownership -u -z".
22
23Usage:
24    keyctl add trusted name "new keylen [options]" ring
25    keyctl add trusted name "load hex_blob [pcrlock=pcrnum]" ring
26    keyctl update key "update [options]"
27    keyctl print keyid
28
29    options:
30       keyhandle= ascii hex value of sealing key default 0x40000000 (SRK)
31       keyauth= ascii hex auth for sealing key default 0x00...i
32          (40 ascii zeros)
33       blobauth= ascii hex auth for sealed data default 0x00...
34          (40 ascii zeros)
35       blobauth= ascii hex auth for sealed data default 0x00...
36          (40 ascii zeros)
37       pcrinfo= ascii hex of PCR_INFO or PCR_INFO_LONG (no default)
38       pcrlock= pcr number to be extended to "lock" blob
39       migratable= 0|1 indicating permission to reseal to new PCR values,
40                   default 1 (resealing allowed)
41
42"keyctl print" returns an ascii hex copy of the sealed key, which is in standard
43TPM_STORED_DATA format. The key length for new keys are always in bytes.
44Trusted Keys can be 32 - 128 bytes (256 - 1024 bits), the upper limit is to fit
45within the 2048 bit SRK (RSA) keylength, with all necessary structure/padding.
46
47Encrypted keys do not depend on a TPM, and are faster, as they use AES for
48encryption/decryption. New keys are created from kernel generated random
49numbers, and are encrypted/decrypted using a specified 'master' key. The
50'master' key can either be a trusted-key or user-key type. The main
51disadvantage of encrypted keys is that if they are not rooted in a trusted key,
52they are only as secure as the user key encrypting them. The master user key
53should therefore be loaded in as secure a way as possible, preferably early in
54boot.
55
56Usage:
57  keyctl add encrypted name "new key-type:master-key-name keylen" ring
58  keyctl add encrypted name "load hex_blob" ring
59  keyctl update keyid "update key-type:master-key-name"
60
61where 'key-type' is either 'trusted' or 'user'.
62
63Examples of trusted and encrypted key usage:
64
65Create and save a trusted key named "kmk" of length 32 bytes:
66
67    $ keyctl add trusted kmk "new 32" @u
68    440502848
69
70    $ keyctl show
71    Session Keyring
72           -3 --alswrv 500 500 keyring: _ses
73     97833714 --alswrv 500 -1 \_ keyring: _uid.500
74    440502848 --alswrv 500 500 \_ trusted: kmk
75
76    $ keyctl print 440502848
77    0101000000000000000001005d01b7e3f4a6be5709930f3b70a743cbb42e0cc95e18e915
78    3f60da455bbf1144ad12e4f92b452f966929f6105fd29ca28e4d4d5a031d068478bacb0b
79    27351119f822911b0a11ba3d3498ba6a32e50dac7f32894dd890eb9ad578e4e292c83722
80    a52e56a097e6a68b3f56f7a52ece0cdccba1eb62cad7d817f6dc58898b3ac15f36026fec
81    d568bd4a706cb60bb37be6d8f1240661199d640b66fb0fe3b079f97f450b9ef9c22c6d5d
82    dd379f0facd1cd020281dfa3c70ba21a3fa6fc2471dc6d13ecf8298b946f65345faa5ef0
83    f1f8fff03ad0acb083725535636addb08d73dedb9832da198081e5deae84bfaf0409c22b
84    e4a8aea2b607ec96931e6f4d4fe563ba
85
86    $ keyctl pipe 440502848 > kmk.blob
87
88Load a trusted key from the saved blob:
89
90    $ keyctl add trusted kmk "load `cat kmk.blob`" @u
91    268728824
92
93    $ keyctl print 268728824
94    0101000000000000000001005d01b7e3f4a6be5709930f3b70a743cbb42e0cc95e18e915
95    3f60da455bbf1144ad12e4f92b452f966929f6105fd29ca28e4d4d5a031d068478bacb0b
96    27351119f822911b0a11ba3d3498ba6a32e50dac7f32894dd890eb9ad578e4e292c83722
97    a52e56a097e6a68b3f56f7a52ece0cdccba1eb62cad7d817f6dc58898b3ac15f36026fec
98    d568bd4a706cb60bb37be6d8f1240661199d640b66fb0fe3b079f97f450b9ef9c22c6d5d
99    dd379f0facd1cd020281dfa3c70ba21a3fa6fc2471dc6d13ecf8298b946f65345faa5ef0
100    f1f8fff03ad0acb083725535636addb08d73dedb9832da198081e5deae84bfaf0409c22b
101    e4a8aea2b607ec96931e6f4d4fe563ba
102
103Reseal a trusted key under new pcr values:
104
105    $ keyctl update 268728824 "update pcrinfo=`cat pcr.blob`"
106    $ keyctl print 268728824
107    010100000000002c0002800093c35a09b70fff26e7a98ae786c641e678ec6ffb6b46d805
108    77c8a6377aed9d3219c6dfec4b23ffe3000001005d37d472ac8a44023fbb3d18583a4f73
109    d3a076c0858f6f1dcaa39ea0f119911ff03f5406df4f7f27f41da8d7194f45c9f4e00f2e
110    df449f266253aa3f52e55c53de147773e00f0f9aca86c64d94c95382265968c354c5eab4
111    9638c5ae99c89de1e0997242edfb0b501744e11ff9762dfd951cffd93227cc513384e7e6
112    e782c29435c7ec2edafaa2f4c1fe6e7a781b59549ff5296371b42133777dcc5b8b971610
113    94bc67ede19e43ddb9dc2baacad374a36feaf0314d700af0a65c164b7082401740e489c9
114    7ef6a24defe4846104209bf0c3eced7fa1a672ed5b125fc9d8cd88b476a658a4434644ef
115    df8ae9a178e9f83ba9f08d10fa47e4226b98b0702f06b3b8
116
117Create and save an encrypted key "evm" using the above trusted key "kmk":
118
119    $ keyctl add encrypted evm "new trusted:kmk 32" @u
120    159771175
121
122    $ keyctl print 159771175
123    trusted:kmk 32 2375725ad57798846a9bbd240de8906f006e66c03af53b1b382dbbc55
124    be2a44616e4959430436dc4f2a7a9659aa60bb4652aeb2120f149ed197c564e024717c64
125    5972dcb82ab2dde83376d82b2e3c09ffc
126
127    $ keyctl pipe 159771175 > evm.blob
128
129Load an encrypted key "evm" from saved blob:
130
131    $ keyctl add encrypted evm "load `cat evm.blob`" @u
132    831684262
133
134    $ keyctl print 831684262
135    trusted:kmk 32 2375725ad57798846a9bbd240de8906f006e66c03af53b1b382dbbc55
136    be2a44616e4959430436dc4f2a7a9659aa60bb4652aeb2120f149ed197c564e024717c64
137    5972dcb82ab2dde83376d82b2e3c09ffc
138
139
140The initial consumer of trusted keys is EVM, which at boot time needs a high
141quality symmetric key for HMAC protection of file metadata. The use of a
142trusted key provides strong guarantees that the EVM key has not been
143compromised by a user level problem, and when sealed to specific boot PCR
144values, protects against boot and offline attacks. Other uses for trusted and
145encrypted keys, such as for disk and file encryption are anticipated.
146

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