Documentation/security/keys/trusted-encrypted.rst - third_party/linux - Git at Google

 ==========================
 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.

 TPM 1.2
 -------

 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".

 TPM 2.0
 -------

 The user must first create a storage key and make it persistent, so the key is
 available after reboot. This can be done using the following commands.

 With the IBM TSS 2 stack::

   #> tsscreateprimary -hi o -st
   Handle 80000000
   #> tssevictcontrol -hi o -ho 80000000 -hp 81000001

 Or with the Intel TSS 2 stack::

   #> tpm2_createprimary --hierarchy o -G rsa2048 -o key.ctxt
   [...]
   handle: 0x800000FF
   #> tpm2_evictcontrol -c key.ctxt -p 0x81000001
   persistentHandle: 0x81000001

 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
                        TPM 1.2: default 0x40000000 (SRK)
                        TPM 2.0: no default; must be passed every time
        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)
        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"

 Where::

 	format:= 'default | ecryptfs | enc32'
 	key-type:= 'trusted' | 'user'


 Examples of trusted and encrypted key usage:

 Create and save a trusted key named "kmk" of length 32 bytes.

 Note: When using a TPM 2.0 with a persistent key with handle 0x81000001,
 append 'keyhandle=0x81000001' to statements between quotes, such as
 "new 32 keyhandle=0x81000001".

 ::

     $ 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.rst``.

 Another new format 'enc32' has been defined in order to support encrypted keys
 with payload size of 32 bytes. This will initially be used for nvdimm security
 but may expand to other usages that require 32 bytes payload.
	==========================
	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.

	TPM 1.2
	-------

	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".

	TPM 2.0
	-------

	The user must first create a storage key and make it persistent, so the key is
	available after reboot. This can be done using the following commands.

	With the IBM TSS 2 stack::

	#> tsscreateprimary -hi o -st
	Handle 80000000
	#> tssevictcontrol -hi o -ho 80000000 -hp 81000001

	Or with the Intel TSS 2 stack::

	#> tpm2_createprimary --hierarchy o -G rsa2048 -o key.ctxt
	[...]
	handle: 0x800000FF
	#> tpm2_evictcontrol -c key.ctxt -p 0x81000001
	persistentHandle: 0x81000001

	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
	TPM 1.2: default 0x40000000 (SRK)
	TPM 2.0: no default; must be passed every time
	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)
	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"

	Where::

	format:= 'default \| ecryptfs \| enc32'
	key-type:= 'trusted' \| 'user'


	Examples of trusted and encrypted key usage:

	Create and save a trusted key named "kmk" of length 32 bytes.

	Note: When using a TPM 2.0 with a persistent key with handle 0x81000001,
	append 'keyhandle=0x81000001' to statements between quotes, such as
	"new 32 keyhandle=0x81000001".

	::

	$ 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.rst``.

	Another new format 'enc32' has been defined in order to support encrypted keys
	with payload size of 32 bytes. This will initially be used for nvdimm security
	but may expand to other usages that require 32 bytes payload.