123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960616263646566676869707172737475767778798081828384858687888990919293949596979899100101102103104105106107108109110111112113114115116117118119120121122123124125126127128129130131132133134135136137138139140141142143144145146147148149150151152153154155156157158159160161162163164165166167168169 |
- Trusted and Encrypted Keys
- Trusted and Encrypted Keys are two new key types added to the existing kernel
- key ring service. Both of these new types are variable length symmetric keys,
- and in both cases all keys are created in the kernel, and user space sees,
- stores, and loads only encrypted blobs. Trusted Keys require the availability
- of a Trusted Platform Module (TPM) chip for greater security, while Encrypted
- Keys can be used on any system. All user level blobs, are displayed and loaded
- in hex ascii for convenience, and are integrity verified.
- Trusted Keys use a TPM both to generate and to seal the keys. Keys are sealed
- under a 2048 bit RSA key in the TPM, and optionally sealed to specified PCR
- (integrity measurement) values, and only unsealed by the TPM, if PCRs and blob
- integrity verifications match. A loaded Trusted Key can be updated with new
- (future) PCR values, so keys are easily migrated to new pcr values, such as
- when the kernel and initramfs are updated. The same key can have many saved
- blobs under different PCR values, so multiple boots are easily supported.
- By default, trusted keys are sealed under the SRK, which has the default
- authorization value (20 zeros). This can be set at takeownership time with the
- trouser's utility: "tpm_takeownership -u -z".
- Usage:
- keyctl add trusted name "new keylen [options]" ring
- keyctl add trusted name "load hex_blob [pcrlock=pcrnum]" ring
- keyctl update key "update [options]"
- keyctl print keyid
- options:
- keyhandle= ascii hex value of sealing key default 0x40000000 (SRK)
- keyauth= ascii hex auth for sealing key default 0x00...i
- (40 ascii zeros)
- blobauth= ascii hex auth for sealed data default 0x00...
- (40 ascii zeros)
- blobauth= ascii hex auth for sealed data default 0x00...
- (40 ascii zeros)
- pcrinfo= ascii hex of PCR_INFO or PCR_INFO_LONG (no default)
- pcrlock= pcr number to be extended to "lock" blob
- migratable= 0|1 indicating permission to reseal to new PCR values,
- default 1 (resealing allowed)
- hash= hash algorithm name as a string. For TPM 1.x the only
- allowed value is sha1. For TPM 2.x the allowed values
- are sha1, sha256, sha384, sha512 and sm3-256.
- policydigest= digest for the authorization policy. must be calculated
- with the same hash algorithm as specified by the 'hash='
- option.
- policyhandle= handle to an authorization policy session that defines the
- same policy and with the same hash algorithm as was used to
- seal the key.
- "keyctl print" returns an ascii hex copy of the sealed key, which is in standard
- TPM_STORED_DATA format. The key length for new keys are always in bytes.
- Trusted Keys can be 32 - 128 bytes (256 - 1024 bits), the upper limit is to fit
- within the 2048 bit SRK (RSA) keylength, with all necessary structure/padding.
- Encrypted keys do not depend on a TPM, and are faster, as they use AES for
- encryption/decryption. New keys are created from kernel generated random
- numbers, and are encrypted/decrypted using a specified 'master' key. The
- 'master' key can either be a trusted-key or user-key type. The main
- disadvantage of encrypted keys is that if they are not rooted in a trusted key,
- they are only as secure as the user key encrypting them. The master user key
- should therefore be loaded in as secure a way as possible, preferably early in
- boot.
- The decrypted portion of encrypted keys can contain either a simple symmetric
- key or a more complex structure. The format of the more complex structure is
- application specific, which is identified by 'format'.
- Usage:
- keyctl add encrypted name "new [format] key-type:master-key-name keylen"
- ring
- keyctl add encrypted name "load hex_blob" ring
- keyctl update keyid "update key-type:master-key-name"
- format:= 'default | ecryptfs'
- key-type:= 'trusted' | 'user'
- Examples of trusted and encrypted key usage:
- Create and save a trusted key named "kmk" of length 32 bytes:
- $ keyctl add trusted kmk "new 32" @u
- 440502848
- $ keyctl show
- Session Keyring
- -3 --alswrv 500 500 keyring: _ses
- 97833714 --alswrv 500 -1 \_ keyring: _uid.500
- 440502848 --alswrv 500 500 \_ trusted: kmk
- $ keyctl print 440502848
- 0101000000000000000001005d01b7e3f4a6be5709930f3b70a743cbb42e0cc95e18e915
- 3f60da455bbf1144ad12e4f92b452f966929f6105fd29ca28e4d4d5a031d068478bacb0b
- 27351119f822911b0a11ba3d3498ba6a32e50dac7f32894dd890eb9ad578e4e292c83722
- a52e56a097e6a68b3f56f7a52ece0cdccba1eb62cad7d817f6dc58898b3ac15f36026fec
- d568bd4a706cb60bb37be6d8f1240661199d640b66fb0fe3b079f97f450b9ef9c22c6d5d
- dd379f0facd1cd020281dfa3c70ba21a3fa6fc2471dc6d13ecf8298b946f65345faa5ef0
- f1f8fff03ad0acb083725535636addb08d73dedb9832da198081e5deae84bfaf0409c22b
- e4a8aea2b607ec96931e6f4d4fe563ba
- $ keyctl pipe 440502848 > kmk.blob
- Load a trusted key from the saved blob:
- $ keyctl add trusted kmk "load `cat kmk.blob`" @u
- 268728824
- $ keyctl print 268728824
- 0101000000000000000001005d01b7e3f4a6be5709930f3b70a743cbb42e0cc95e18e915
- 3f60da455bbf1144ad12e4f92b452f966929f6105fd29ca28e4d4d5a031d068478bacb0b
- 27351119f822911b0a11ba3d3498ba6a32e50dac7f32894dd890eb9ad578e4e292c83722
- a52e56a097e6a68b3f56f7a52ece0cdccba1eb62cad7d817f6dc58898b3ac15f36026fec
- d568bd4a706cb60bb37be6d8f1240661199d640b66fb0fe3b079f97f450b9ef9c22c6d5d
- dd379f0facd1cd020281dfa3c70ba21a3fa6fc2471dc6d13ecf8298b946f65345faa5ef0
- f1f8fff03ad0acb083725535636addb08d73dedb9832da198081e5deae84bfaf0409c22b
- e4a8aea2b607ec96931e6f4d4fe563ba
- Reseal a trusted key under new pcr values:
- $ keyctl update 268728824 "update pcrinfo=`cat pcr.blob`"
- $ keyctl print 268728824
- 010100000000002c0002800093c35a09b70fff26e7a98ae786c641e678ec6ffb6b46d805
- 77c8a6377aed9d3219c6dfec4b23ffe3000001005d37d472ac8a44023fbb3d18583a4f73
- d3a076c0858f6f1dcaa39ea0f119911ff03f5406df4f7f27f41da8d7194f45c9f4e00f2e
- df449f266253aa3f52e55c53de147773e00f0f9aca86c64d94c95382265968c354c5eab4
- 9638c5ae99c89de1e0997242edfb0b501744e11ff9762dfd951cffd93227cc513384e7e6
- e782c29435c7ec2edafaa2f4c1fe6e7a781b59549ff5296371b42133777dcc5b8b971610
- 94bc67ede19e43ddb9dc2baacad374a36feaf0314d700af0a65c164b7082401740e489c9
- 7ef6a24defe4846104209bf0c3eced7fa1a672ed5b125fc9d8cd88b476a658a4434644ef
- df8ae9a178e9f83ba9f08d10fa47e4226b98b0702f06b3b8
- The initial consumer of trusted keys is EVM, which at boot time needs a high
- quality symmetric key for HMAC protection of file metadata. The use of a
- trusted key provides strong guarantees that the EVM key has not been
- compromised by a user level problem, and when sealed to specific boot PCR
- values, protects against boot and offline attacks. Create and save an
- encrypted key "evm" using the above trusted key "kmk":
- option 1: omitting 'format'
- $ keyctl add encrypted evm "new trusted:kmk 32" @u
- 159771175
- option 2: explicitly defining 'format' as 'default'
- $ keyctl add encrypted evm "new default trusted:kmk 32" @u
- 159771175
- $ keyctl print 159771175
- default trusted:kmk 32 2375725ad57798846a9bbd240de8906f006e66c03af53b1b3
- 82dbbc55be2a44616e4959430436dc4f2a7a9659aa60bb4652aeb2120f149ed197c564e0
- 24717c64 5972dcb82ab2dde83376d82b2e3c09ffc
- $ keyctl pipe 159771175 > evm.blob
- Load an encrypted key "evm" from saved blob:
- $ keyctl add encrypted evm "load `cat evm.blob`" @u
- 831684262
- $ keyctl print 831684262
- default trusted:kmk 32 2375725ad57798846a9bbd240de8906f006e66c03af53b1b3
- 82dbbc55be2a44616e4959430436dc4f2a7a9659aa60bb4652aeb2120f149ed197c564e0
- 24717c64 5972dcb82ab2dde83376d82b2e3c09ffc
- Other uses for trusted and encrypted keys, such as for disk and file encryption
- are anticipated. In particular the new format 'ecryptfs' has been defined in
- in order to use encrypted keys to mount an eCryptfs filesystem. More details
- about the usage can be found in the file
- 'Documentation/security/keys-ecryptfs.txt'.
|