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Define a new kernel key-type called 'trusted'. Trusted keys are random
number symmetric keys, generated and RSA-sealed by the TPM. The TPM
only unseals the keys, if the boot PCRs and other criteria match.
Userspace can only ever see encrypted blobs.
Based on suggestions by Jason Gunthorpe, several new options have been
added to support additional usages.
The new options are:
migratable= designates that the key may/may not ever be updated
(resealed under a new key, new pcrinfo or new auth.)
pcrlock=n extends the designated PCR 'n' with a random value,
so that a key sealed to that PCR may not be unsealed
again until after a reboot.
keyhandle= specifies the sealing/unsealing key handle.
keyauth= specifies the sealing/unsealing key auth.
blobauth= specifies the sealed data auth.
Implementation of a kernel reserved locality for trusted keys will be
investigated for a possible future extension.
Changelog:
- Updated and added examples to Documentation/keys-trusted-encrypted.txt
- Moved generic TPM constants to include/linux/tpm_command.h
(David Howell's suggestion.)
- trusted_defined.c: replaced kzalloc with kmalloc, added pcrlock failure
error handling, added const qualifiers where appropriate.
- moved to late_initcall
- updated from hash to shash (suggestion by David Howells)
- reduced worst stack usage (tpm_seal) from 530 to 312 bytes
- moved documentation to Documentation directory (suggestion by David Howells)
- all the other code cleanups suggested by David Howells
- Add pcrlock CAP_SYS_ADMIN dependency (based on comment by Jason Gunthorpe)
- New options: migratable, pcrlock, keyhandle, keyauth, blobauth (based on
discussions with Jason Gunthorpe)
- Free payload on failure to create key(reported/fixed by Roberto Sassu)
- Updated Kconfig and other descriptions (based on Serge Hallyn's suggestion)
- Replaced kzalloc() with kmalloc() (reported by Serge Hallyn)
Signed-off-by: David Safford <safford@watson.ibm.com>
Signed-off-by: Mimi Zohar <zohar@us.ibm.com>
Signed-off-by: James Morris <jmorris@namei.org>
146 lines
6.7 KiB
Plaintext
146 lines
6.7 KiB
Plaintext
Trusted and Encrypted Keys
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Trusted and Encrypted Keys are two new key types added to the existing kernel
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key ring service. Both of these new types are variable length symmetic keys,
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and in both cases all keys are created in the kernel, and user space sees,
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stores, and loads only encrypted blobs. Trusted Keys require the availability
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of a Trusted Platform Module (TPM) chip for greater security, while Encrypted
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Keys can be used on any system. All user level blobs, are displayed and loaded
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in hex ascii for convenience, and are integrity verified.
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Trusted Keys use a TPM both to generate and to seal the keys. Keys are sealed
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under a 2048 bit RSA key in the TPM, and optionally sealed to specified PCR
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(integrity measurement) values, and only unsealed by the TPM, if PCRs and blob
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integrity verifications match. A loaded Trusted Key can be updated with new
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(future) PCR values, so keys are easily migrated to new pcr values, such as
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when the kernel and initramfs are updated. The same key can have many saved
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blobs under different PCR values, so multiple boots are easily supported.
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By default, trusted keys are sealed under the SRK, which has the default
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authorization value (20 zeros). This can be set at takeownership time with the
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trouser's utility: "tpm_takeownership -u -z".
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Usage:
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keyctl add trusted name "new keylen [options]" ring
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keyctl add trusted name "load hex_blob [pcrlock=pcrnum]" ring
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keyctl update key "update [options]"
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keyctl print keyid
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options:
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keyhandle= ascii hex value of sealing key default 0x40000000 (SRK)
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keyauth= ascii hex auth for sealing key default 0x00...i
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(40 ascii zeros)
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blobauth= ascii hex auth for sealed data default 0x00...
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(40 ascii zeros)
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blobauth= ascii hex auth for sealed data default 0x00...
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(40 ascii zeros)
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pcrinfo= ascii hex of PCR_INFO or PCR_INFO_LONG (no default)
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pcrlock= pcr number to be extended to "lock" blob
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migratable= 0|1 indicating permission to reseal to new PCR values,
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default 1 (resealing allowed)
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"keyctl print" returns an ascii hex copy of the sealed key, which is in standard
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TPM_STORED_DATA format. The key length for new keys are always in bytes.
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Trusted Keys can be 32 - 128 bytes (256 - 1024 bits), the upper limit is to fit
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within the 2048 bit SRK (RSA) keylength, with all necessary structure/padding.
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Encrypted keys do not depend on a TPM, and are faster, as they use AES for
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encryption/decryption. New keys are created from kernel generated random
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numbers, and are encrypted/decrypted using a specified 'master' key. The
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'master' key can either be a trusted-key or user-key type. The main
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disadvantage of encrypted keys is that if they are not rooted in a trusted key,
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they are only as secure as the user key encrypting them. The master user key
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should therefore be loaded in as secure a way as possible, preferably early in
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boot.
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Usage:
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keyctl add encrypted name "new key-type:master-key-name keylen" ring
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keyctl add encrypted name "load hex_blob" ring
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keyctl update keyid "update key-type:master-key-name"
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where 'key-type' is either 'trusted' or 'user'.
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Examples of trusted and encrypted key usage:
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Create and save a trusted key named "kmk" of length 32 bytes:
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$ keyctl add trusted kmk "new 32" @u
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440502848
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$ keyctl show
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Session Keyring
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-3 --alswrv 500 500 keyring: _ses
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97833714 --alswrv 500 -1 \_ keyring: _uid.500
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440502848 --alswrv 500 500 \_ trusted: kmk
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$ keyctl print 440502848
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0101000000000000000001005d01b7e3f4a6be5709930f3b70a743cbb42e0cc95e18e915
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3f60da455bbf1144ad12e4f92b452f966929f6105fd29ca28e4d4d5a031d068478bacb0b
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27351119f822911b0a11ba3d3498ba6a32e50dac7f32894dd890eb9ad578e4e292c83722
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a52e56a097e6a68b3f56f7a52ece0cdccba1eb62cad7d817f6dc58898b3ac15f36026fec
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d568bd4a706cb60bb37be6d8f1240661199d640b66fb0fe3b079f97f450b9ef9c22c6d5d
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dd379f0facd1cd020281dfa3c70ba21a3fa6fc2471dc6d13ecf8298b946f65345faa5ef0
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f1f8fff03ad0acb083725535636addb08d73dedb9832da198081e5deae84bfaf0409c22b
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e4a8aea2b607ec96931e6f4d4fe563ba
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$ keyctl pipe 440502848 > kmk.blob
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Load a trusted key from the saved blob:
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$ keyctl add trusted kmk "load `cat kmk.blob`" @u
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268728824
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$ keyctl print 268728824
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0101000000000000000001005d01b7e3f4a6be5709930f3b70a743cbb42e0cc95e18e915
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3f60da455bbf1144ad12e4f92b452f966929f6105fd29ca28e4d4d5a031d068478bacb0b
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27351119f822911b0a11ba3d3498ba6a32e50dac7f32894dd890eb9ad578e4e292c83722
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a52e56a097e6a68b3f56f7a52ece0cdccba1eb62cad7d817f6dc58898b3ac15f36026fec
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d568bd4a706cb60bb37be6d8f1240661199d640b66fb0fe3b079f97f450b9ef9c22c6d5d
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dd379f0facd1cd020281dfa3c70ba21a3fa6fc2471dc6d13ecf8298b946f65345faa5ef0
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f1f8fff03ad0acb083725535636addb08d73dedb9832da198081e5deae84bfaf0409c22b
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e4a8aea2b607ec96931e6f4d4fe563ba
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Reseal a trusted key under new pcr values:
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$ keyctl update 268728824 "update pcrinfo=`cat pcr.blob`"
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$ keyctl print 268728824
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010100000000002c0002800093c35a09b70fff26e7a98ae786c641e678ec6ffb6b46d805
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77c8a6377aed9d3219c6dfec4b23ffe3000001005d37d472ac8a44023fbb3d18583a4f73
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d3a076c0858f6f1dcaa39ea0f119911ff03f5406df4f7f27f41da8d7194f45c9f4e00f2e
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df449f266253aa3f52e55c53de147773e00f0f9aca86c64d94c95382265968c354c5eab4
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9638c5ae99c89de1e0997242edfb0b501744e11ff9762dfd951cffd93227cc513384e7e6
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e782c29435c7ec2edafaa2f4c1fe6e7a781b59549ff5296371b42133777dcc5b8b971610
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94bc67ede19e43ddb9dc2baacad374a36feaf0314d700af0a65c164b7082401740e489c9
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7ef6a24defe4846104209bf0c3eced7fa1a672ed5b125fc9d8cd88b476a658a4434644ef
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df8ae9a178e9f83ba9f08d10fa47e4226b98b0702f06b3b8
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Create and save an encrypted key "evm" using the above trusted key "kmk":
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$ keyctl add encrypted evm "new trusted:kmk 32" @u
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159771175
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$ keyctl print 159771175
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trusted:kmk 32 2375725ad57798846a9bbd240de8906f006e66c03af53b1b382dbbc55
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be2a44616e4959430436dc4f2a7a9659aa60bb4652aeb2120f149ed197c564e024717c64
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5972dcb82ab2dde83376d82b2e3c09ffc
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$ keyctl pipe 159771175 > evm.blob
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Load an encrypted key "evm" from saved blob:
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$ keyctl add encrypted evm "load `cat evm.blob`" @u
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831684262
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$ keyctl print 831684262
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trusted:kmk 32 2375725ad57798846a9bbd240de8906f006e66c03af53b1b382dbbc55
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be2a44616e4959430436dc4f2a7a9659aa60bb4652aeb2120f149ed197c564e024717c64
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5972dcb82ab2dde83376d82b2e3c09ffc
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The initial consumer of trusted keys is EVM, which at boot time needs a high
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quality symmetric key for HMAC protection of file metadata. The use of a
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trusted key provides strong guarantees that the EVM key has not been
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compromised by a user level problem, and when sealed to specific boot PCR
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values, protects against boot and offline attacks. Other uses for trusted and
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encrypted keys, such as for disk and file encryption are anticipated.
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