About Kernel Documentation Linux Kernel Contact Linux Resources Linux Blog

Documentation / security / keys-trusted-encrypted.txt




Custom Search

Based on kernel version 4.7.2. Page generated on 2016-08-22 22:47 EST.

1				Trusted and Encrypted Keys
2	
3	Trusted and Encrypted Keys are two new key types added to the existing kernel
4	key ring service.  Both of these new types are variable length symmetric keys,
5	and in both cases all keys are created in the kernel, and user space sees,
6	stores, and loads only encrypted blobs.  Trusted Keys require the availability
7	of a Trusted Platform Module (TPM) chip for greater security, while Encrypted
8	Keys can be used on any system.  All user level blobs, are displayed and loaded
9	in hex ascii for convenience, and are integrity verified.
10	
11	Trusted Keys use a TPM both to generate and to seal the keys.  Keys are sealed
12	under 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
14	integrity 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
16	when the kernel and initramfs are updated.  The same key can have many saved
17	blobs under different PCR values, so multiple boots are easily supported.
18	
19	By default, trusted keys are sealed under the SRK, which has the default
20	authorization value (20 zeros).  This can be set at takeownership time with the
21	trouser's utility: "tpm_takeownership -u -z".
22	
23	Usage:
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	       hash=         hash algorithm name as a string. For TPM 1.x the only
42	                     allowed value is sha1. For TPM 2.x the allowed values
43	                     are sha1, sha256, sha384, sha512 and sm3-256.
44	       policydigest= digest for the authorization policy. must be calculated
45	                     with the same hash algorithm as specified by the 'hash='
46	                     option.
47	       policyhandle= handle to an authorization policy session that defines the
48	                     same policy and with the same hash algorithm as was used to
49	                     seal the key.
50	
51	"keyctl print" returns an ascii hex copy of the sealed key, which is in standard
52	TPM_STORED_DATA format.  The key length for new keys are always in bytes.
53	Trusted Keys can be 32 - 128 bytes (256 - 1024 bits), the upper limit is to fit
54	within the 2048 bit SRK (RSA) keylength, with all necessary structure/padding.
55	
56	Encrypted keys do not depend on a TPM, and are faster, as they use AES for
57	encryption/decryption.  New keys are created from kernel generated random
58	numbers, and are encrypted/decrypted using a specified 'master' key.  The
59	'master' key can either be a trusted-key or user-key type.  The main
60	disadvantage of encrypted keys is that if they are not rooted in a trusted key,
61	they are only as secure as the user key encrypting them.  The master user key
62	should therefore be loaded in as secure a way as possible, preferably early in
63	boot.
64	
65	The decrypted portion of encrypted keys can contain either a simple symmetric
66	key or a more complex structure. The format of the more complex structure is
67	application specific, which is identified by 'format'.
68	
69	Usage:
70	    keyctl add encrypted name "new [format] key-type:master-key-name keylen"
71	        ring
72	    keyctl add encrypted name "load hex_blob" ring
73	    keyctl update keyid "update key-type:master-key-name"
74	
75	format:= 'default | ecryptfs'
76	key-type:= 'trusted' | 'user'
77	
78	
79	Examples of trusted and encrypted key usage:
80	
81	Create and save a trusted key named "kmk" of length 32 bytes:
82	
83	    $ keyctl add trusted kmk "new 32" @u
84	    440502848
85	
86	    $ keyctl show
87	    Session Keyring
88	           -3 --alswrv    500   500  keyring: _ses
89	     97833714 --alswrv    500    -1   \_ keyring: _uid.500
90	    440502848 --alswrv    500   500       \_ trusted: kmk
91	
92	    $ keyctl print 440502848
93	    0101000000000000000001005d01b7e3f4a6be5709930f3b70a743cbb42e0cc95e18e915
94	    3f60da455bbf1144ad12e4f92b452f966929f6105fd29ca28e4d4d5a031d068478bacb0b
95	    27351119f822911b0a11ba3d3498ba6a32e50dac7f32894dd890eb9ad578e4e292c83722
96	    a52e56a097e6a68b3f56f7a52ece0cdccba1eb62cad7d817f6dc58898b3ac15f36026fec
97	    d568bd4a706cb60bb37be6d8f1240661199d640b66fb0fe3b079f97f450b9ef9c22c6d5d
98	    dd379f0facd1cd020281dfa3c70ba21a3fa6fc2471dc6d13ecf8298b946f65345faa5ef0
99	    f1f8fff03ad0acb083725535636addb08d73dedb9832da198081e5deae84bfaf0409c22b
100	    e4a8aea2b607ec96931e6f4d4fe563ba
101	
102	    $ keyctl pipe 440502848 > kmk.blob
103	
104	Load a trusted key from the saved blob:
105	
106	    $ keyctl add trusted kmk "load `cat kmk.blob`" @u
107	    268728824
108	
109	    $ keyctl print 268728824
110	    0101000000000000000001005d01b7e3f4a6be5709930f3b70a743cbb42e0cc95e18e915
111	    3f60da455bbf1144ad12e4f92b452f966929f6105fd29ca28e4d4d5a031d068478bacb0b
112	    27351119f822911b0a11ba3d3498ba6a32e50dac7f32894dd890eb9ad578e4e292c83722
113	    a52e56a097e6a68b3f56f7a52ece0cdccba1eb62cad7d817f6dc58898b3ac15f36026fec
114	    d568bd4a706cb60bb37be6d8f1240661199d640b66fb0fe3b079f97f450b9ef9c22c6d5d
115	    dd379f0facd1cd020281dfa3c70ba21a3fa6fc2471dc6d13ecf8298b946f65345faa5ef0
116	    f1f8fff03ad0acb083725535636addb08d73dedb9832da198081e5deae84bfaf0409c22b
117	    e4a8aea2b607ec96931e6f4d4fe563ba
118	
119	Reseal a trusted key under new pcr values:
120	
121	    $ keyctl update 268728824 "update pcrinfo=`cat pcr.blob`"
122	    $ keyctl print 268728824
123	    010100000000002c0002800093c35a09b70fff26e7a98ae786c641e678ec6ffb6b46d805
124	    77c8a6377aed9d3219c6dfec4b23ffe3000001005d37d472ac8a44023fbb3d18583a4f73
125	    d3a076c0858f6f1dcaa39ea0f119911ff03f5406df4f7f27f41da8d7194f45c9f4e00f2e
126	    df449f266253aa3f52e55c53de147773e00f0f9aca86c64d94c95382265968c354c5eab4
127	    9638c5ae99c89de1e0997242edfb0b501744e11ff9762dfd951cffd93227cc513384e7e6
128	    e782c29435c7ec2edafaa2f4c1fe6e7a781b59549ff5296371b42133777dcc5b8b971610
129	    94bc67ede19e43ddb9dc2baacad374a36feaf0314d700af0a65c164b7082401740e489c9
130	    7ef6a24defe4846104209bf0c3eced7fa1a672ed5b125fc9d8cd88b476a658a4434644ef
131	    df8ae9a178e9f83ba9f08d10fa47e4226b98b0702f06b3b8
132	
133	The initial consumer of trusted keys is EVM, which at boot time needs a high
134	quality symmetric key for HMAC protection of file metadata.  The use of a
135	trusted key provides strong guarantees that the EVM key has not been
136	compromised by a user level problem, and when sealed to specific boot PCR
137	values, protects against boot and offline attacks.  Create and save an
138	encrypted key "evm" using the above trusted key "kmk":
139	
140	option 1: omitting 'format'
141	    $ keyctl add encrypted evm "new trusted:kmk 32" @u
142	    159771175
143	
144	option 2: explicitly defining 'format' as 'default'
145	    $ keyctl add encrypted evm "new default trusted:kmk 32" @u
146	    159771175
147	
148	    $ keyctl print 159771175
149	    default trusted:kmk 32 2375725ad57798846a9bbd240de8906f006e66c03af53b1b3
150	    82dbbc55be2a44616e4959430436dc4f2a7a9659aa60bb4652aeb2120f149ed197c564e0
151	    24717c64 5972dcb82ab2dde83376d82b2e3c09ffc
152	
153	    $ keyctl pipe 159771175 > evm.blob
154	
155	Load an encrypted key "evm" from saved blob:
156	
157	    $ keyctl add encrypted evm "load `cat evm.blob`" @u
158	    831684262
159	
160	    $ keyctl print 831684262
161	    default trusted:kmk 32 2375725ad57798846a9bbd240de8906f006e66c03af53b1b3
162	    82dbbc55be2a44616e4959430436dc4f2a7a9659aa60bb4652aeb2120f149ed197c564e0
163	    24717c64 5972dcb82ab2dde83376d82b2e3c09ffc
164	
165	Other uses for trusted and encrypted keys, such as for disk and file encryption
166	are anticipated.  In particular the new format 'ecryptfs' has been defined in
167	in order to use encrypted keys to mount an eCryptfs filesystem.  More details
168	about the usage can be found in the file
169	'Documentation/security/keys-ecryptfs.txt'.
Hide Line Numbers
About Kernel Documentation Linux Kernel Contact Linux Resources Linux Blog

Information is copyright its respective author. All material is available from the Linux Kernel Source distributed under a GPL License. This page is provided as a free service by mjmwired.net.