Documentation/security/keys/trusted-encrypted.rst - 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 Trust Source 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.


 Trust Source
 ============

 A trust source provides the source of security for Trusted Keys.  This
 section lists currently supported trust sources, along with their security
 considerations.  Whether or not a trust source is sufficiently safe depends
 on the strength and correctness of its implementation, as well as the threat
 environment for a specific use case.  Since the kernel doesn't know what the
 environment is, and there is no metric of trust, it is dependent on the
 consumer of the Trusted Keys to determine if the trust source is sufficiently
 safe.

   *  Root of trust for storage

      (1) TPM (Trusted Platform Module: hardware device)

          Rooted to Storage Root Key (SRK) which never leaves the TPM that
          provides crypto operation to establish root of trust for storage.

      (2) TEE (Trusted Execution Environment: OP-TEE based on Arm TrustZone)

          Rooted to Hardware Unique Key (HUK) which is generally burnt in on-chip
          fuses and is accessible to TEE only.

      (3) CAAM (Cryptographic Acceleration and Assurance Module: IP on NXP SoCs)

          When High Assurance Boot (HAB) is enabled and the CAAM is in secure
          mode, trust is rooted to the OTPMK, a never-disclosed 256-bit key
          randomly generated and fused into each SoC at manufacturing time.
          Otherwise, a common fixed test key is used instead.

      (4) DCP (Data Co-Processor: crypto accelerator of various i.MX SoCs)

          Rooted to a one-time programmable key (OTP) that is generally burnt
          in the on-chip fuses and is accessible to the DCP encryption engine only.
          DCP provides two keys that can be used as root of trust: the OTP key
          and the UNIQUE key. Default is to use the UNIQUE key, but selecting
          the OTP key can be done via a module parameter (dcp_use_otp_key).

   *  Execution isolation

      (1) TPM

          Fixed set of operations running in isolated execution environment.

      (2) TEE

          Customizable set of operations running in isolated execution
          environment verified via Secure/Trusted boot process.

      (3) CAAM

          Fixed set of operations running in isolated execution environment.

      (4) DCP

          Fixed set of cryptographic operations running in isolated execution
          environment. Only basic blob key encryption is executed there.
          The actual key sealing/unsealing is done on main processor/kernel space.

   * Optional binding to platform integrity state

      (1) TPM

          Keys can be 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.

      (2) TEE

          Relies on Secure/Trusted boot process for platform integrity. It can
          be extended with TEE based measured boot process.

      (3) CAAM

          Relies on the High Assurance Boot (HAB) mechanism of NXP SoCs
          for platform integrity.

      (4) DCP

          Relies on Secure/Trusted boot process (called HAB by vendor) for
          platform integrity.

   *  Interfaces and APIs

      (1) TPM

          TPMs have well-documented, standardized interfaces and APIs.

      (2) TEE

          TEEs have well-documented, standardized client interface and APIs. For
          more details refer to ``Documentation/driver-api/tee.rst``.

      (3) CAAM

          Interface is specific to silicon vendor.

      (4) DCP

          Vendor-specific API that is implemented as part of the DCP crypto driver in
          ``drivers/crypto/mxs-dcp.c``.

   *  Threat model

      The strength and appropriateness of a particular trust source for a given
      purpose must be assessed when using them to protect security-relevant data.


 Key Generation
 ==============

 Trusted Keys
 ------------

 New keys are created from random numbers. They are encrypted/decrypted using
 a child key in the storage key hierarchy. Encryption and decryption of the
 child key must be protected by a strong access control policy within the
 trust source. The random number generator in use differs according to the
 selected trust source:

   *  TPM: hardware device based RNG

      Keys are generated within the TPM. Strength of random numbers may vary
      from one device manufacturer to another.

   *  TEE: OP-TEE based on Arm TrustZone based RNG

      RNG is customizable as per platform needs. It can either be direct output
      from platform specific hardware RNG or a software based Fortuna CSPRNG
      which can be seeded via multiple entropy sources.

   *  CAAM: Kernel RNG

      The normal kernel random number generator is used. To seed it from the
      CAAM HWRNG, enable CRYPTO_DEV_FSL_CAAM_RNG_API and ensure the device
      is probed.

   *  DCP (Data Co-Processor: crypto accelerator of various i.MX SoCs)

      The DCP hardware device itself does not provide a dedicated RNG interface,
      so the kernel default RNG is used. SoCs with DCP like the i.MX6ULL do have
      a dedicated hardware RNG that is independent from DCP which can be enabled
      to back the kernel RNG.

 Users may override this by specifying ``trusted.rng=kernel`` on the kernel
 command-line to override the used RNG with the kernel's random number pool.

 Encrypted Keys
 --------------

 Encrypted keys do not depend on a trust source, and are faster, as they use AES
 for encryption/decryption. New keys are created either from kernel-generated
 random numbers or user-provided decrypted data, 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.


 Usage
 =====

 Trusted Keys usage: TPM
 -----------------------

 TPM 1.2: By default, trusted keys are sealed under the SRK, which has the
 default authorization value (20 bytes of 0s).  This can be set at takeownership
 time with the TrouSerS 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 -c key.ctxt
   [...]
   #> tpm2_evictcontrol -c key.ctxt 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.

 Trusted Keys usage: TEE
 -----------------------

 Usage::

     keyctl add trusted name "new keylen" ring
     keyctl add trusted name "load hex_blob" ring
     keyctl print keyid

 "keyctl print" returns an ASCII hex copy of the sealed key, which is in format
 specific to TEE device implementation.  The key length for new keys is always
 in bytes. Trusted Keys can be 32 - 128 bytes (256 - 1024 bits).

 Trusted Keys usage: CAAM
 ------------------------

 Usage::

     keyctl add trusted name "new keylen" ring
     keyctl add trusted name "load hex_blob" ring
     keyctl print keyid

 "keyctl print" returns an ASCII hex copy of the sealed key, which is in a
 CAAM-specific format.  The key length for new keys is always in bytes.
 Trusted Keys can be 32 - 128 bytes (256 - 1024 bits).

 Trusted Keys usage: DCP
 -----------------------

 Usage::

     keyctl add trusted name "new keylen" ring
     keyctl add trusted name "load hex_blob" ring
     keyctl print keyid

 "keyctl print" returns an ASCII hex copy of the sealed key, which is in format
 specific to this DCP key-blob implementation.  The key length for new keys is
 always in bytes. Trusted Keys can be 32 - 128 bytes (256 - 1024 bits).

 Encrypted Keys usage
 --------------------

 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 "new [format] key-type:master-key-name keylen
         decrypted-data" 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 (TPM specific) 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 a platform integrity
 state, 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

 Instantiate an encrypted key "evm" using user-provided decrypted data::

     $ evmkey=$(dd if=/dev/urandom bs=1 count=32 | xxd -c32 -p)
     $ keyctl add encrypted evm "new default user:kmk 32 $evmkey" @u
     794890253

     $ keyctl print 794890253
     default user:kmk 32 2375725ad57798846a9bbd240de8906f006e66c03af53b1b382d
     bbc55be2a44616e4959430436dc4f2a7a9659aa60bb4652aeb2120f149ed197c564e0247
     17c64 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 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.


 TPM 2.0 ASN.1 Key Format
 ------------------------

 The TPM 2.0 ASN.1 key format is designed to be easily recognisable,
 even in binary form (fixing a problem we had with the TPM 1.2 ASN.1
 format) and to be extensible for additions like importable keys and
 policy::

     TPMKey ::= SEQUENCE {
         type		OBJECT IDENTIFIER
         emptyAuth	[0] EXPLICIT BOOLEAN OPTIONAL
         parent		INTEGER
         pubkey		OCTET STRING
         privkey		OCTET STRING
     }

 type is what distinguishes the key even in binary form since the OID
 is provided by the TCG to be unique and thus forms a recognizable
 binary pattern at offset 3 in the key.  The OIDs currently made
 available are::

     2.23.133.10.1.3 TPM Loadable key.  This is an asymmetric key (Usually
                     RSA2048 or Elliptic Curve) which can be imported by a
                     TPM2_Load() operation.

     2.23.133.10.1.4 TPM Importable Key.  This is an asymmetric key (Usually
                     RSA2048 or Elliptic Curve) which can be imported by a
                     TPM2_Import() operation.

     2.23.133.10.1.5 TPM Sealed Data.  This is a set of data (up to 128
                     bytes) which is sealed by the TPM.  It usually
                     represents a symmetric key and must be unsealed before
                     use.

 The trusted key code only uses the TPM Sealed Data OID.

 emptyAuth is true if the key has well known authorization "".  If it
 is false or not present, the key requires an explicit authorization
 phrase.  This is used by most user space consumers to decide whether
 to prompt for a password.

 parent represents the parent key handle, either in the 0x81 MSO space,
 like 0x81000001 for the RSA primary storage key.  Userspace programmes
 also support specifying the primary handle in the 0x40 MSO space.  If
 this happens the Elliptic Curve variant of the primary key using the
 TCG defined template will be generated on the fly into a volatile
 object and used as the parent.  The current kernel code only supports
 the 0x81 MSO form.

 pubkey is the binary representation of TPM2B_PRIVATE excluding the
 initial TPM2B header, which can be reconstructed from the ASN.1 octet
 string length.

 privkey is the binary representation of TPM2B_PUBLIC excluding the
 initial TPM2B header which can be reconstructed from the ASN.1 octed
 string length.

 DCP Blob Format
 ---------------

 .. kernel-doc:: security/keys/trusted-keys/trusted_dcp.c
    :doc: dcp blob format

 .. kernel-doc:: security/keys/trusted-keys/trusted_dcp.c
    :identifiers: struct dcp_blob_fmt
	==========================
	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 Trust Source 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.


	Trust Source
	============

	A trust source provides the source of security for Trusted Keys. This
	section lists currently supported trust sources, along with their security
	considerations. Whether or not a trust source is sufficiently safe depends
	on the strength and correctness of its implementation, as well as the threat
	environment for a specific use case. Since the kernel doesn't know what the
	environment is, and there is no metric of trust, it is dependent on the
	consumer of the Trusted Keys to determine if the trust source is sufficiently
	safe.

	* Root of trust for storage

	(1) TPM (Trusted Platform Module: hardware device)

	Rooted to Storage Root Key (SRK) which never leaves the TPM that
	provides crypto operation to establish root of trust for storage.

	(2) TEE (Trusted Execution Environment: OP-TEE based on Arm TrustZone)

	Rooted to Hardware Unique Key (HUK) which is generally burnt in on-chip
	fuses and is accessible to TEE only.

	(3) CAAM (Cryptographic Acceleration and Assurance Module: IP on NXP SoCs)

	When High Assurance Boot (HAB) is enabled and the CAAM is in secure
	mode, trust is rooted to the OTPMK, a never-disclosed 256-bit key
	randomly generated and fused into each SoC at manufacturing time.
	Otherwise, a common fixed test key is used instead.

	(4) DCP (Data Co-Processor: crypto accelerator of various i.MX SoCs)

	Rooted to a one-time programmable key (OTP) that is generally burnt
	in the on-chip fuses and is accessible to the DCP encryption engine only.
	DCP provides two keys that can be used as root of trust: the OTP key
	and the UNIQUE key. Default is to use the UNIQUE key, but selecting
	the OTP key can be done via a module parameter (dcp_use_otp_key).

	* Execution isolation

	(1) TPM

	Fixed set of operations running in isolated execution environment.

	(2) TEE

	Customizable set of operations running in isolated execution
	environment verified via Secure/Trusted boot process.

	(3) CAAM

	Fixed set of operations running in isolated execution environment.

	(4) DCP

	Fixed set of cryptographic operations running in isolated execution
	environment. Only basic blob key encryption is executed there.
	The actual key sealing/unsealing is done on main processor/kernel space.

	* Optional binding to platform integrity state

	(1) TPM

	Keys can be 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.

	(2) TEE

	Relies on Secure/Trusted boot process for platform integrity. It can
	be extended with TEE based measured boot process.

	(3) CAAM

	Relies on the High Assurance Boot (HAB) mechanism of NXP SoCs
	for platform integrity.

	(4) DCP

	Relies on Secure/Trusted boot process (called HAB by vendor) for
	platform integrity.

	* Interfaces and APIs

	(1) TPM

	TPMs have well-documented, standardized interfaces and APIs.

	(2) TEE

	TEEs have well-documented, standardized client interface and APIs. For
	more details refer to ``Documentation/driver-api/tee.rst``.

	(3) CAAM

	Interface is specific to silicon vendor.

	(4) DCP

	Vendor-specific API that is implemented as part of the DCP crypto driver in
	``drivers/crypto/mxs-dcp.c``.

	* Threat model

	The strength and appropriateness of a particular trust source for a given
	purpose must be assessed when using them to protect security-relevant data.


	Key Generation
	==============

	Trusted Keys
	------------

	New keys are created from random numbers. They are encrypted/decrypted using
	a child key in the storage key hierarchy. Encryption and decryption of the
	child key must be protected by a strong access control policy within the
	trust source. The random number generator in use differs according to the
	selected trust source:

	* TPM: hardware device based RNG

	Keys are generated within the TPM. Strength of random numbers may vary
	from one device manufacturer to another.

	* TEE: OP-TEE based on Arm TrustZone based RNG

	RNG is customizable as per platform needs. It can either be direct output
	from platform specific hardware RNG or a software based Fortuna CSPRNG
	which can be seeded via multiple entropy sources.

	* CAAM: Kernel RNG

	The normal kernel random number generator is used. To seed it from the
	CAAM HWRNG, enable CRYPTO_DEV_FSL_CAAM_RNG_API and ensure the device
	is probed.

	* DCP (Data Co-Processor: crypto accelerator of various i.MX SoCs)

	The DCP hardware device itself does not provide a dedicated RNG interface,
	so the kernel default RNG is used. SoCs with DCP like the i.MX6ULL do have
	a dedicated hardware RNG that is independent from DCP which can be enabled
	to back the kernel RNG.

	Users may override this by specifying ``trusted.rng=kernel`` on the kernel
	command-line to override the used RNG with the kernel's random number pool.

	Encrypted Keys
	--------------

	Encrypted keys do not depend on a trust source, and are faster, as they use AES
	for encryption/decryption. New keys are created either from kernel-generated
	random numbers or user-provided decrypted data, 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.


	Usage
	=====

	Trusted Keys usage: TPM
	-----------------------

	TPM 1.2: By default, trusted keys are sealed under the SRK, which has the
	default authorization value (20 bytes of 0s). This can be set at takeownership
	time with the TrouSerS 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 -c key.ctxt
	[...]
	#> tpm2_evictcontrol -c key.ctxt 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.

	Trusted Keys usage: TEE
	-----------------------

	Usage::

	keyctl add trusted name "new keylen" ring
	keyctl add trusted name "load hex_blob" ring
	keyctl print keyid

	"keyctl print" returns an ASCII hex copy of the sealed key, which is in format
	specific to TEE device implementation. The key length for new keys is always
	in bytes. Trusted Keys can be 32 - 128 bytes (256 - 1024 bits).

	Trusted Keys usage: CAAM
	------------------------

	Usage::

	keyctl add trusted name "new keylen" ring
	keyctl add trusted name "load hex_blob" ring
	keyctl print keyid

	"keyctl print" returns an ASCII hex copy of the sealed key, which is in a
	CAAM-specific format. The key length for new keys is always in bytes.
	Trusted Keys can be 32 - 128 bytes (256 - 1024 bits).

	Trusted Keys usage: DCP
	-----------------------

	Usage::

	keyctl add trusted name "new keylen" ring
	keyctl add trusted name "load hex_blob" ring
	keyctl print keyid

	"keyctl print" returns an ASCII hex copy of the sealed key, which is in format
	specific to this DCP key-blob implementation. The key length for new keys is
	always in bytes. Trusted Keys can be 32 - 128 bytes (256 - 1024 bits).

	Encrypted Keys usage
	--------------------

	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 "new [format] key-type:master-key-name keylen
	decrypted-data" 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 (TPM specific) 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 a platform integrity
	state, 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

	Instantiate an encrypted key "evm" using user-provided decrypted data::

	$ evmkey=$(dd if=/dev/urandom bs=1 count=32 \| xxd -c32 -p)
	$ keyctl add encrypted evm "new default user:kmk 32 $evmkey" @u
	794890253

	$ keyctl print 794890253
	default user:kmk 32 2375725ad57798846a9bbd240de8906f006e66c03af53b1b382d
	bbc55be2a44616e4959430436dc4f2a7a9659aa60bb4652aeb2120f149ed197c564e0247
	17c64 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 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.


	TPM 2.0 ASN.1 Key Format
	------------------------

	The TPM 2.0 ASN.1 key format is designed to be easily recognisable,
	even in binary form (fixing a problem we had with the TPM 1.2 ASN.1
	format) and to be extensible for additions like importable keys and
	policy::

	TPMKey ::= SEQUENCE {
	type OBJECT IDENTIFIER
	emptyAuth [0] EXPLICIT BOOLEAN OPTIONAL
	parent INTEGER
	pubkey OCTET STRING
	privkey OCTET STRING
	}

	type is what distinguishes the key even in binary form since the OID
	is provided by the TCG to be unique and thus forms a recognizable
	binary pattern at offset 3 in the key. The OIDs currently made
	available are::

	2.23.133.10.1.3 TPM Loadable key. This is an asymmetric key (Usually
	RSA2048 or Elliptic Curve) which can be imported by a
	TPM2_Load() operation.

	2.23.133.10.1.4 TPM Importable Key. This is an asymmetric key (Usually
	RSA2048 or Elliptic Curve) which can be imported by a
	TPM2_Import() operation.

	2.23.133.10.1.5 TPM Sealed Data. This is a set of data (up to 128
	bytes) which is sealed by the TPM. It usually
	represents a symmetric key and must be unsealed before
	use.

	The trusted key code only uses the TPM Sealed Data OID.

	emptyAuth is true if the key has well known authorization "". If it
	is false or not present, the key requires an explicit authorization
	phrase. This is used by most user space consumers to decide whether
	to prompt for a password.

	parent represents the parent key handle, either in the 0x81 MSO space,
	like 0x81000001 for the RSA primary storage key. Userspace programmes
	also support specifying the primary handle in the 0x40 MSO space. If
	this happens the Elliptic Curve variant of the primary key using the
	TCG defined template will be generated on the fly into a volatile
	object and used as the parent. The current kernel code only supports
	the 0x81 MSO form.

	pubkey is the binary representation of TPM2B_PRIVATE excluding the
	initial TPM2B header, which can be reconstructed from the ASN.1 octet
	string length.

	privkey is the binary representation of TPM2B_PUBLIC excluding the
	initial TPM2B header which can be reconstructed from the ASN.1 octed
	string length.

	DCP Blob Format
	---------------

	.. kernel-doc:: security/keys/trusted-keys/trusted_dcp.c
	:doc: dcp blob format

	.. kernel-doc:: security/keys/trusted-keys/trusted_dcp.c
	:identifiers: struct dcp_blob_fmt