xref: /linux/Documentation/security/keys/trusted-encrypted.rst (revision b2d0f5d5dc53532e6f07bc546a476a55ebdfe0f3) 
1==========================
2Trusted and Encrypted Keys
3==========================
4
5Trusted and Encrypted Keys are two new key types added to the existing kernel
6key ring service.  Both of these new types are variable length symmetric keys,
7and in both cases all keys are created in the kernel, and user space sees,
8stores, and loads only encrypted blobs.  Trusted Keys require the availability
9of a Trusted Platform Module (TPM) chip for greater security, while Encrypted
10Keys can be used on any system.  All user level blobs, are displayed and loaded
11in hex ascii for convenience, and are integrity verified.
12
13Trusted Keys use a TPM both to generate and to seal the keys.  Keys are sealed
14under a 2048 bit RSA key in the TPM, and optionally sealed to specified PCR
15(integrity measurement) values, and only unsealed by the TPM, if PCRs and blob
16integrity verifications match.  A loaded Trusted Key can be updated with new
17(future) PCR values, so keys are easily migrated to new pcr values, such as
18when the kernel and initramfs are updated.  The same key can have many saved
19blobs under different PCR values, so multiple boots are easily supported.
20
21By default, trusted keys are sealed under the SRK, which has the default
22authorization value (20 zeros).  This can be set at takeownership time with the
23trouser's utility: "tpm_takeownership -u -z".
24
25Usage::
26
27    keyctl add trusted name "new keylen [options]" ring
28    keyctl add trusted name "load hex_blob [pcrlock=pcrnum]" ring
29    keyctl update key "update [options]"
30    keyctl print keyid
31
32    options:
33       keyhandle=    ascii hex value of sealing key default 0x40000000 (SRK)
34       keyauth=	     ascii hex auth for sealing key default 0x00...i
35                     (40 ascii zeros)
36       blobauth=     ascii hex auth for sealed data default 0x00...
37                     (40 ascii zeros)
38       pcrinfo=	     ascii hex of PCR_INFO or PCR_INFO_LONG (no default)
39       pcrlock=	     pcr number to be extended to "lock" blob
40       migratable=   0|1 indicating permission to reseal to new PCR values,
41                     default 1 (resealing allowed)
42       hash=         hash algorithm name as a string. For TPM 1.x the only
43                     allowed value is sha1. For TPM 2.x the allowed values
44                     are sha1, sha256, sha384, sha512 and sm3-256.
45       policydigest= digest for the authorization policy. must be calculated
46                     with the same hash algorithm as specified by the 'hash='
47                     option.
48       policyhandle= handle to an authorization policy session that defines the
49                     same policy and with the same hash algorithm as was used to
50                     seal the key.
51
52"keyctl print" returns an ascii hex copy of the sealed key, which is in standard
53TPM_STORED_DATA format.  The key length for new keys are always in bytes.
54Trusted Keys can be 32 - 128 bytes (256 - 1024 bits), the upper limit is to fit
55within the 2048 bit SRK (RSA) keylength, with all necessary structure/padding.
56
57Encrypted keys do not depend on a TPM, and are faster, as they use AES for
58encryption/decryption.  New keys are created from kernel generated random
59numbers, and are encrypted/decrypted using a specified 'master' key.  The
60'master' key can either be a trusted-key or user-key type.  The main
61disadvantage of encrypted keys is that if they are not rooted in a trusted key,
62they are only as secure as the user key encrypting them.  The master user key
63should therefore be loaded in as secure a way as possible, preferably early in
64boot.
65
66The decrypted portion of encrypted keys can contain either a simple symmetric
67key or a more complex structure. The format of the more complex structure is
68application specific, which is identified by 'format'.
69
70Usage::
71
72    keyctl add encrypted name "new [format] key-type:master-key-name keylen"
73        ring
74    keyctl add encrypted name "load hex_blob" ring
75    keyctl update keyid "update key-type:master-key-name"
76
77Where::
78
79	format:= 'default | ecryptfs'
80	key-type:= 'trusted' | 'user'
81
82
83Examples of trusted and encrypted key usage:
84
85Create and save a trusted key named "kmk" of length 32 bytes::
86
87    $ keyctl add trusted kmk "new 32" @u
88    440502848
89
90    $ keyctl show
91    Session Keyring
92           -3 --alswrv    500   500  keyring: _ses
93     97833714 --alswrv    500    -1   \_ keyring: _uid.500
94    440502848 --alswrv    500   500       \_ trusted: kmk
95
96    $ keyctl print 440502848
97    0101000000000000000001005d01b7e3f4a6be5709930f3b70a743cbb42e0cc95e18e915
98    3f60da455bbf1144ad12e4f92b452f966929f6105fd29ca28e4d4d5a031d068478bacb0b
99    27351119f822911b0a11ba3d3498ba6a32e50dac7f32894dd890eb9ad578e4e292c83722
100    a52e56a097e6a68b3f56f7a52ece0cdccba1eb62cad7d817f6dc58898b3ac15f36026fec
101    d568bd4a706cb60bb37be6d8f1240661199d640b66fb0fe3b079f97f450b9ef9c22c6d5d
102    dd379f0facd1cd020281dfa3c70ba21a3fa6fc2471dc6d13ecf8298b946f65345faa5ef0
103    f1f8fff03ad0acb083725535636addb08d73dedb9832da198081e5deae84bfaf0409c22b
104    e4a8aea2b607ec96931e6f4d4fe563ba
105
106    $ keyctl pipe 440502848 > kmk.blob
107
108Load a trusted key from the saved blob::
109
110    $ keyctl add trusted kmk "load `cat kmk.blob`" @u
111    268728824
112
113    $ keyctl print 268728824
114    0101000000000000000001005d01b7e3f4a6be5709930f3b70a743cbb42e0cc95e18e915
115    3f60da455bbf1144ad12e4f92b452f966929f6105fd29ca28e4d4d5a031d068478bacb0b
116    27351119f822911b0a11ba3d3498ba6a32e50dac7f32894dd890eb9ad578e4e292c83722
117    a52e56a097e6a68b3f56f7a52ece0cdccba1eb62cad7d817f6dc58898b3ac15f36026fec
118    d568bd4a706cb60bb37be6d8f1240661199d640b66fb0fe3b079f97f450b9ef9c22c6d5d
119    dd379f0facd1cd020281dfa3c70ba21a3fa6fc2471dc6d13ecf8298b946f65345faa5ef0
120    f1f8fff03ad0acb083725535636addb08d73dedb9832da198081e5deae84bfaf0409c22b
121    e4a8aea2b607ec96931e6f4d4fe563ba
122
123Reseal a trusted key under new pcr values::
124
125    $ keyctl update 268728824 "update pcrinfo=`cat pcr.blob`"
126    $ keyctl print 268728824
127    010100000000002c0002800093c35a09b70fff26e7a98ae786c641e678ec6ffb6b46d805
128    77c8a6377aed9d3219c6dfec4b23ffe3000001005d37d472ac8a44023fbb3d18583a4f73
129    d3a076c0858f6f1dcaa39ea0f119911ff03f5406df4f7f27f41da8d7194f45c9f4e00f2e
130    df449f266253aa3f52e55c53de147773e00f0f9aca86c64d94c95382265968c354c5eab4
131    9638c5ae99c89de1e0997242edfb0b501744e11ff9762dfd951cffd93227cc513384e7e6
132    e782c29435c7ec2edafaa2f4c1fe6e7a781b59549ff5296371b42133777dcc5b8b971610
133    94bc67ede19e43ddb9dc2baacad374a36feaf0314d700af0a65c164b7082401740e489c9
134    7ef6a24defe4846104209bf0c3eced7fa1a672ed5b125fc9d8cd88b476a658a4434644ef
135    df8ae9a178e9f83ba9f08d10fa47e4226b98b0702f06b3b8
136
137The initial consumer of trusted keys is EVM, which at boot time needs a high
138quality symmetric key for HMAC protection of file metadata.  The use of a
139trusted key provides strong guarantees that the EVM key has not been
140compromised by a user level problem, and when sealed to specific boot PCR
141values, protects against boot and offline attacks.  Create and save an
142encrypted key "evm" using the above trusted key "kmk":
143
144option 1: omitting 'format'::
145
146    $ keyctl add encrypted evm "new trusted:kmk 32" @u
147    159771175
148
149option 2: explicitly defining 'format' as 'default'::
150
151    $ keyctl add encrypted evm "new default trusted:kmk 32" @u
152    159771175
153
154    $ keyctl print 159771175
155    default trusted:kmk 32 2375725ad57798846a9bbd240de8906f006e66c03af53b1b3
156    82dbbc55be2a44616e4959430436dc4f2a7a9659aa60bb4652aeb2120f149ed197c564e0
157    24717c64 5972dcb82ab2dde83376d82b2e3c09ffc
158
159    $ keyctl pipe 159771175 > evm.blob
160
161Load an encrypted key "evm" from saved blob::
162
163    $ keyctl add encrypted evm "load `cat evm.blob`" @u
164    831684262
165
166    $ keyctl print 831684262
167    default trusted:kmk 32 2375725ad57798846a9bbd240de8906f006e66c03af53b1b3
168    82dbbc55be2a44616e4959430436dc4f2a7a9659aa60bb4652aeb2120f149ed197c564e0
169    24717c64 5972dcb82ab2dde83376d82b2e3c09ffc
170
171Other uses for trusted and encrypted keys, such as for disk and file encryption
172are anticipated.  In particular the new format 'ecryptfs' has been defined in
173in order to use encrypted keys to mount an eCryptfs filesystem.  More details
174about the usage can be found in the file
175``Documentation/security/keys/ecryptfs.rst``.
176