linux/Documentation/keys-trusted-encrypted.txt
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   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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