xref: /linux/Documentation/security/keys/trusted-encrypted.rst (revision ec8a42e7343234802b9054874fe01810880289ce) 
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
21TPM 1.2
22-------
23
24By default, trusted keys are sealed under the SRK, which has the default
25authorization value (20 zeros).  This can be set at takeownership time with the
26trouser's utility: "tpm_takeownership -u -z".
27
28TPM 2.0
29-------
30
31The user must first create a storage key and make it persistent, so the key is
32available after reboot. This can be done using the following commands.
33
34With the IBM TSS 2 stack::
35
36  #> tsscreateprimary -hi o -st
37  Handle 80000000
38  #> tssevictcontrol -hi o -ho 80000000 -hp 81000001
39
40Or with the Intel TSS 2 stack::
41
42  #> tpm2_createprimary --hierarchy o -G rsa2048 -c key.ctxt
43  [...]
44  #> tpm2_evictcontrol -c key.ctxt 0x81000001
45  persistentHandle: 0x81000001
46
47Usage::
48
49    keyctl add trusted name "new keylen [options]" ring
50    keyctl add trusted name "load hex_blob [pcrlock=pcrnum]" ring
51    keyctl update key "update [options]"
52    keyctl print keyid
53
54    options:
55       keyhandle=    ascii hex value of sealing key
56                       TPM 1.2: default 0x40000000 (SRK)
57                       TPM 2.0: no default; must be passed every time
58       keyauth=	     ascii hex auth for sealing key default 0x00...i
59                     (40 ascii zeros)
60       blobauth=     ascii hex auth for sealed data default 0x00...
61                     (40 ascii zeros)
62       pcrinfo=	     ascii hex of PCR_INFO or PCR_INFO_LONG (no default)
63       pcrlock=	     pcr number to be extended to "lock" blob
64       migratable=   0|1 indicating permission to reseal to new PCR values,
65                     default 1 (resealing allowed)
66       hash=         hash algorithm name as a string. For TPM 1.x the only
67                     allowed value is sha1. For TPM 2.x the allowed values
68                     are sha1, sha256, sha384, sha512 and sm3-256.
69       policydigest= digest for the authorization policy. must be calculated
70                     with the same hash algorithm as specified by the 'hash='
71                     option.
72       policyhandle= handle to an authorization policy session that defines the
73                     same policy and with the same hash algorithm as was used to
74                     seal the key.
75
76"keyctl print" returns an ascii hex copy of the sealed key, which is in standard
77TPM_STORED_DATA format.  The key length for new keys are always in bytes.
78Trusted Keys can be 32 - 128 bytes (256 - 1024 bits), the upper limit is to fit
79within the 2048 bit SRK (RSA) keylength, with all necessary structure/padding.
80
81Encrypted keys do not depend on a TPM, and are faster, as they use AES for
82encryption/decryption.  New keys are created from kernel generated random
83numbers, and are encrypted/decrypted using a specified 'master' key.  The
84'master' key can either be a trusted-key or user-key type.  The main
85disadvantage of encrypted keys is that if they are not rooted in a trusted key,
86they are only as secure as the user key encrypting them.  The master user key
87should therefore be loaded in as secure a way as possible, preferably early in
88boot.
89
90The decrypted portion of encrypted keys can contain either a simple symmetric
91key or a more complex structure. The format of the more complex structure is
92application specific, which is identified by 'format'.
93
94Usage::
95
96    keyctl add encrypted name "new [format] key-type:master-key-name keylen"
97        ring
98    keyctl add encrypted name "load hex_blob" ring
99    keyctl update keyid "update key-type:master-key-name"
100
101Where::
102
103	format:= 'default | ecryptfs | enc32'
104	key-type:= 'trusted' | 'user'
105
106
107Examples of trusted and encrypted key usage:
108
109Create and save a trusted key named "kmk" of length 32 bytes.
110
111Note: When using a TPM 2.0 with a persistent key with handle 0x81000001,
112append 'keyhandle=0x81000001' to statements between quotes, such as
113"new 32 keyhandle=0x81000001".
114
115::
116
117    $ keyctl add trusted kmk "new 32" @u
118    440502848
119
120    $ keyctl show
121    Session Keyring
122           -3 --alswrv    500   500  keyring: _ses
123     97833714 --alswrv    500    -1   \_ keyring: _uid.500
124    440502848 --alswrv    500   500       \_ trusted: kmk
125
126    $ keyctl print 440502848
127    0101000000000000000001005d01b7e3f4a6be5709930f3b70a743cbb42e0cc95e18e915
128    3f60da455bbf1144ad12e4f92b452f966929f6105fd29ca28e4d4d5a031d068478bacb0b
129    27351119f822911b0a11ba3d3498ba6a32e50dac7f32894dd890eb9ad578e4e292c83722
130    a52e56a097e6a68b3f56f7a52ece0cdccba1eb62cad7d817f6dc58898b3ac15f36026fec
131    d568bd4a706cb60bb37be6d8f1240661199d640b66fb0fe3b079f97f450b9ef9c22c6d5d
132    dd379f0facd1cd020281dfa3c70ba21a3fa6fc2471dc6d13ecf8298b946f65345faa5ef0
133    f1f8fff03ad0acb083725535636addb08d73dedb9832da198081e5deae84bfaf0409c22b
134    e4a8aea2b607ec96931e6f4d4fe563ba
135
136    $ keyctl pipe 440502848 > kmk.blob
137
138Load a trusted key from the saved blob::
139
140    $ keyctl add trusted kmk "load `cat kmk.blob`" @u
141    268728824
142
143    $ keyctl print 268728824
144    0101000000000000000001005d01b7e3f4a6be5709930f3b70a743cbb42e0cc95e18e915
145    3f60da455bbf1144ad12e4f92b452f966929f6105fd29ca28e4d4d5a031d068478bacb0b
146    27351119f822911b0a11ba3d3498ba6a32e50dac7f32894dd890eb9ad578e4e292c83722
147    a52e56a097e6a68b3f56f7a52ece0cdccba1eb62cad7d817f6dc58898b3ac15f36026fec
148    d568bd4a706cb60bb37be6d8f1240661199d640b66fb0fe3b079f97f450b9ef9c22c6d5d
149    dd379f0facd1cd020281dfa3c70ba21a3fa6fc2471dc6d13ecf8298b946f65345faa5ef0
150    f1f8fff03ad0acb083725535636addb08d73dedb9832da198081e5deae84bfaf0409c22b
151    e4a8aea2b607ec96931e6f4d4fe563ba
152
153Reseal a trusted key under new pcr values::
154
155    $ keyctl update 268728824 "update pcrinfo=`cat pcr.blob`"
156    $ keyctl print 268728824
157    010100000000002c0002800093c35a09b70fff26e7a98ae786c641e678ec6ffb6b46d805
158    77c8a6377aed9d3219c6dfec4b23ffe3000001005d37d472ac8a44023fbb3d18583a4f73
159    d3a076c0858f6f1dcaa39ea0f119911ff03f5406df4f7f27f41da8d7194f45c9f4e00f2e
160    df449f266253aa3f52e55c53de147773e00f0f9aca86c64d94c95382265968c354c5eab4
161    9638c5ae99c89de1e0997242edfb0b501744e11ff9762dfd951cffd93227cc513384e7e6
162    e782c29435c7ec2edafaa2f4c1fe6e7a781b59549ff5296371b42133777dcc5b8b971610
163    94bc67ede19e43ddb9dc2baacad374a36feaf0314d700af0a65c164b7082401740e489c9
164    7ef6a24defe4846104209bf0c3eced7fa1a672ed5b125fc9d8cd88b476a658a4434644ef
165    df8ae9a178e9f83ba9f08d10fa47e4226b98b0702f06b3b8
166
167The initial consumer of trusted keys is EVM, which at boot time needs a high
168quality symmetric key for HMAC protection of file metadata.  The use of a
169trusted key provides strong guarantees that the EVM key has not been
170compromised by a user level problem, and when sealed to specific boot PCR
171values, protects against boot and offline attacks.  Create and save an
172encrypted key "evm" using the above trusted key "kmk":
173
174option 1: omitting 'format'::
175
176    $ keyctl add encrypted evm "new trusted:kmk 32" @u
177    159771175
178
179option 2: explicitly defining 'format' as 'default'::
180
181    $ keyctl add encrypted evm "new default trusted:kmk 32" @u
182    159771175
183
184    $ keyctl print 159771175
185    default trusted:kmk 32 2375725ad57798846a9bbd240de8906f006e66c03af53b1b3
186    82dbbc55be2a44616e4959430436dc4f2a7a9659aa60bb4652aeb2120f149ed197c564e0
187    24717c64 5972dcb82ab2dde83376d82b2e3c09ffc
188
189    $ keyctl pipe 159771175 > evm.blob
190
191Load an encrypted key "evm" from saved blob::
192
193    $ keyctl add encrypted evm "load `cat evm.blob`" @u
194    831684262
195
196    $ keyctl print 831684262
197    default trusted:kmk 32 2375725ad57798846a9bbd240de8906f006e66c03af53b1b3
198    82dbbc55be2a44616e4959430436dc4f2a7a9659aa60bb4652aeb2120f149ed197c564e0
199    24717c64 5972dcb82ab2dde83376d82b2e3c09ffc
200
201Other uses for trusted and encrypted keys, such as for disk and file encryption
202are anticipated.  In particular the new format 'ecryptfs' has been defined
203in order to use encrypted keys to mount an eCryptfs filesystem.  More details
204about the usage can be found in the file
205``Documentation/security/keys/ecryptfs.rst``.
206
207Another new format 'enc32' has been defined in order to support encrypted keys
208with payload size of 32 bytes. This will initially be used for nvdimm security
209but may expand to other usages that require 32 bytes payload.
210