Based on kernel version 4.10.8. Page generated on 2017-04-01 14:44 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 pcrinfo= ascii hex of PCR_INFO or PCR_INFO_LONG (no default) 36 pcrlock= pcr number to be extended to "lock" blob 37 migratable= 0|1 indicating permission to reseal to new PCR values, 38 default 1 (resealing allowed) 39 hash= hash algorithm name as a string. For TPM 1.x the only 40 allowed value is sha1. For TPM 2.x the allowed values 41 are sha1, sha256, sha384, sha512 and sm3-256. 42 policydigest= digest for the authorization policy. must be calculated 43 with the same hash algorithm as specified by the 'hash=' 44 option. 45 policyhandle= handle to an authorization policy session that defines the 46 same policy and with the same hash algorithm as was used to 47 seal the key. 48 49 "keyctl print" returns an ascii hex copy of the sealed key, which is in standard 50 TPM_STORED_DATA format. The key length for new keys are always in bytes. 51 Trusted Keys can be 32 - 128 bytes (256 - 1024 bits), the upper limit is to fit 52 within the 2048 bit SRK (RSA) keylength, with all necessary structure/padding. 53 54 Encrypted keys do not depend on a TPM, and are faster, as they use AES for 55 encryption/decryption. New keys are created from kernel generated random 56 numbers, and are encrypted/decrypted using a specified 'master' key. The 57 'master' key can either be a trusted-key or user-key type. The main 58 disadvantage of encrypted keys is that if they are not rooted in a trusted key, 59 they are only as secure as the user key encrypting them. The master user key 60 should therefore be loaded in as secure a way as possible, preferably early in 61 boot. 62 63 The decrypted portion of encrypted keys can contain either a simple symmetric 64 key or a more complex structure. The format of the more complex structure is 65 application specific, which is identified by 'format'. 66 67 Usage: 68 keyctl add encrypted name "new [format] key-type:master-key-name keylen" 69 ring 70 keyctl add encrypted name "load hex_blob" ring 71 keyctl update keyid "update key-type:master-key-name" 72 73 format:= 'default | ecryptfs' 74 key-type:= 'trusted' | 'user' 75 76 77 Examples of trusted and encrypted key usage: 78 79 Create and save a trusted key named "kmk" of length 32 bytes: 80 81 $ keyctl add trusted kmk "new 32" @u 82 440502848 83 84 $ keyctl show 85 Session Keyring 86 -3 --alswrv 500 500 keyring: _ses 87 97833714 --alswrv 500 -1 \_ keyring: _uid.500 88 440502848 --alswrv 500 500 \_ trusted: kmk 89 90 $ keyctl print 440502848 91 0101000000000000000001005d01b7e3f4a6be5709930f3b70a743cbb42e0cc95e18e915 92 3f60da455bbf1144ad12e4f92b452f966929f6105fd29ca28e4d4d5a031d068478bacb0b 93 27351119f822911b0a11ba3d3498ba6a32e50dac7f32894dd890eb9ad578e4e292c83722 94 a52e56a097e6a68b3f56f7a52ece0cdccba1eb62cad7d817f6dc58898b3ac15f36026fec 95 d568bd4a706cb60bb37be6d8f1240661199d640b66fb0fe3b079f97f450b9ef9c22c6d5d 96 dd379f0facd1cd020281dfa3c70ba21a3fa6fc2471dc6d13ecf8298b946f65345faa5ef0 97 f1f8fff03ad0acb083725535636addb08d73dedb9832da198081e5deae84bfaf0409c22b 98 e4a8aea2b607ec96931e6f4d4fe563ba 99 100 $ keyctl pipe 440502848 > kmk.blob 101 102 Load a trusted key from the saved blob: 103 104 $ keyctl add trusted kmk "load `cat kmk.blob`" @u 105 268728824 106 107 $ keyctl print 268728824 108 0101000000000000000001005d01b7e3f4a6be5709930f3b70a743cbb42e0cc95e18e915 109 3f60da455bbf1144ad12e4f92b452f966929f6105fd29ca28e4d4d5a031d068478bacb0b 110 27351119f822911b0a11ba3d3498ba6a32e50dac7f32894dd890eb9ad578e4e292c83722 111 a52e56a097e6a68b3f56f7a52ece0cdccba1eb62cad7d817f6dc58898b3ac15f36026fec 112 d568bd4a706cb60bb37be6d8f1240661199d640b66fb0fe3b079f97f450b9ef9c22c6d5d 113 dd379f0facd1cd020281dfa3c70ba21a3fa6fc2471dc6d13ecf8298b946f65345faa5ef0 114 f1f8fff03ad0acb083725535636addb08d73dedb9832da198081e5deae84bfaf0409c22b 115 e4a8aea2b607ec96931e6f4d4fe563ba 116 117 Reseal a trusted key under new pcr values: 118 119 $ keyctl update 268728824 "update pcrinfo=`cat pcr.blob`" 120 $ keyctl print 268728824 121 010100000000002c0002800093c35a09b70fff26e7a98ae786c641e678ec6ffb6b46d805 122 77c8a6377aed9d3219c6dfec4b23ffe3000001005d37d472ac8a44023fbb3d18583a4f73 123 d3a076c0858f6f1dcaa39ea0f119911ff03f5406df4f7f27f41da8d7194f45c9f4e00f2e 124 df449f266253aa3f52e55c53de147773e00f0f9aca86c64d94c95382265968c354c5eab4 125 9638c5ae99c89de1e0997242edfb0b501744e11ff9762dfd951cffd93227cc513384e7e6 126 e782c29435c7ec2edafaa2f4c1fe6e7a781b59549ff5296371b42133777dcc5b8b971610 127 94bc67ede19e43ddb9dc2baacad374a36feaf0314d700af0a65c164b7082401740e489c9 128 7ef6a24defe4846104209bf0c3eced7fa1a672ed5b125fc9d8cd88b476a658a4434644ef 129 df8ae9a178e9f83ba9f08d10fa47e4226b98b0702f06b3b8 130 131 The initial consumer of trusted keys is EVM, which at boot time needs a high 132 quality symmetric key for HMAC protection of file metadata. The use of a 133 trusted key provides strong guarantees that the EVM key has not been 134 compromised by a user level problem, and when sealed to specific boot PCR 135 values, protects against boot and offline attacks. Create and save an 136 encrypted key "evm" using the above trusted key "kmk": 137 138 option 1: omitting 'format' 139 $ keyctl add encrypted evm "new trusted:kmk 32" @u 140 159771175 141 142 option 2: explicitly defining 'format' as 'default' 143 $ keyctl add encrypted evm "new default trusted:kmk 32" @u 144 159771175 145 146 $ keyctl print 159771175 147 default trusted:kmk 32 2375725ad57798846a9bbd240de8906f006e66c03af53b1b3 148 82dbbc55be2a44616e4959430436dc4f2a7a9659aa60bb4652aeb2120f149ed197c564e0 149 24717c64 5972dcb82ab2dde83376d82b2e3c09ffc 150 151 $ keyctl pipe 159771175 > evm.blob 152 153 Load an encrypted key "evm" from saved blob: 154 155 $ keyctl add encrypted evm "load `cat evm.blob`" @u 156 831684262 157 158 $ keyctl print 831684262 159 default trusted:kmk 32 2375725ad57798846a9bbd240de8906f006e66c03af53b1b3 160 82dbbc55be2a44616e4959430436dc4f2a7a9659aa60bb4652aeb2120f149ed197c564e0 161 24717c64 5972dcb82ab2dde83376d82b2e3c09ffc 162 163 Other uses for trusted and encrypted keys, such as for disk and file encryption 164 are anticipated. In particular the new format 'ecryptfs' has been defined in 165 in order to use encrypted keys to mount an eCryptfs filesystem. More details 166 about the usage can be found in the file 167 'Documentation/security/keys-ecryptfs.txt'.