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linux-7.2.3/Documentation/security/keys/core.rst
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linux-7.2.3/Documentation/security/keys/ecryptfs.rst
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==========================================
Encrypted keys for the eCryptfs filesystem
==========================================
ECryptfs is a stacked filesystem which transparently encrypts and decrypts each
file using a randomly generated File Encryption Key (FEK).
Each FEK is in turn encrypted with a File Encryption Key Encryption Key (FEKEK)
either in kernel space or in user space with a daemon called 'ecryptfsd'. In
the former case the operation is performed directly by the kernel CryptoAPI
using a key, the FEKEK, derived from a user prompted passphrase; in the latter
the FEK is encrypted by 'ecryptfsd' with the help of external libraries in order
to support other mechanisms like public key cryptography, PKCS#11 and TPM based
operations.
The data structure defined by eCryptfs to contain information required for the
FEK decryption is called authentication token and, currently, can be stored in a
kernel key of the 'user' type, inserted in the user's session specific keyring
by the userspace utility 'mount.ecryptfs' shipped with the package
'ecryptfs-utils'.
The 'encrypted' key type has been extended with the introduction of the new
format 'ecryptfs' in order to be used in conjunction with the eCryptfs
filesystem. Encrypted keys of the newly introduced format store an
authentication token in its payload with a FEKEK randomly generated by the
kernel and protected by the parent master key.
In order to avoid known-plaintext attacks, the datablob obtained through
commands 'keyctl print' or 'keyctl pipe' does not contain the overall
authentication token, which content is well known, but only the FEKEK in
encrypted form.
The eCryptfs filesystem may really benefit from using encrypted keys in that the
required key can be securely generated by an Administrator and provided at boot
time after the unsealing of a 'trusted' key in order to perform the mount in a
controlled environment. Another advantage is that the key is not exposed to
threats of malicious software, because it is available in clear form only at
kernel level.
Usage::
keyctl add encrypted name "new ecryptfs 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::
name:= '<16 hexadecimal characters>'
key-type:= 'trusted' | 'user'
keylen:= 64
Example of encrypted key usage with the eCryptfs filesystem:
Create an encrypted key "1000100010001000" of length 64 bytes with format
'ecryptfs' and save it using a previously loaded user key "test"::
$ keyctl add encrypted 1000100010001000 "new ecryptfs user:test 64" @u
19184530
$ keyctl print 19184530
ecryptfs user:test 64 490045d4bfe48c99f0d465fbbbb79e7500da954178e2de0697
dd85091f5450a0511219e9f7cd70dcd498038181466f78ac8d4c19504fcc72402bfc41c2
f253a41b7507ccaa4b2b03fff19a69d1cc0b16e71746473f023a95488b6edfd86f7fdd40
9d292e4bacded1258880122dd553a661
$ keyctl pipe 19184530 > ecryptfs.blob
Mount an eCryptfs filesystem using the created encrypted key "1000100010001000"
into the '/secret' directory::
$ mount -i -t ecryptfs -oecryptfs_sig=1000100010001000,\
ecryptfs_cipher=aes,ecryptfs_key_bytes=32 /secret /secret
linux-7.2.3/Documentation/security/keys/index.rst
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===========
Kernel Keys
===========
.. toctree::
:maxdepth: 1
core
ecryptfs
request-key
trusted-encrypted
linux-7.2.3/Documentation/security/keys/request-key.rst
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===================
Key Request Service
===================
The key request service is part of the key retention service (refer to
Documentation/security/keys/core.rst). This document explains more fully how
the requesting algorithm works.
The process starts by either the kernel requesting a service by calling
``request_key*()``::
struct key *request_key(const struct key_type *type,
const char *description,
const char *callout_info);
or::
struct key *request_key_tag(const struct key_type *type,
const char *description,
const struct key_tag *domain_tag,
const char *callout_info);
or::
struct key *request_key_with_auxdata(const struct key_type *type,
const char *description,
const struct key_tag *domain_tag,
const char *callout_info,
size_t callout_len,
void *aux);
or::
struct key *request_key_rcu(const struct key_type *type,
const char *description,
const struct key_tag *domain_tag);
Or by userspace invoking the request_key system call::
key_serial_t request_key(const char *type,
const char *description,
const char *callout_info,
key_serial_t dest_keyring);
The main difference between the access points is that the in-kernel interface
does not need to link the key to a keyring to prevent it from being immediately
destroyed. The kernel interface returns a pointer directly to the key, and
it's up to the caller to destroy the key.
The request_key_tag() call is like the in-kernel request_key(), except that it
also takes a domain tag that allows keys to be separated by namespace and
killed off as a group.
The request_key_with_auxdata() calls is like the request_key_tag() call, except
that they permit auxiliary data to be passed to the upcaller (the default is
NULL). This is only useful for those key types that define their own upcall
mechanism rather than using /sbin/request-key.
The request_key_rcu() call is like the request_key_tag() call, except that it
doesn't check for keys that are under construction and doesn't attempt to
construct missing keys.
The userspace interface links the key to a keyring associated with the process
to prevent the key from going away, and returns the serial number of the key to
the caller.
The following example assumes that the key types involved don't define their
own upcall mechanisms. If they do, then those should be substituted for the
forking and execution of /sbin/request-key.
The Process
===========
A request proceeds in the following manner:
1) Process A calls request_key() [the userspace syscall calls the kernel
interface].
2) request_key() searches the process's subscribed keyrings to see if there's
a suitable key there. If there is, it returns the key. If there isn't,
and callout_info is not set, an error is returned. Otherwise the process
proceeds to the next step.
3) request_key() sees that A doesn't have the desired key yet, so it creates
two things:
a) An uninstantiated key U of requested type and description.
b) An authorisation key V that refers to key U and notes that process A
is the context in which key U should be instantiated and secured, and
from which associated key requests may be satisfied.
4) request_key() then forks and executes /sbin/request-key with a new session
keyring that contains a link to auth key V.
5) /sbin/request-key assumes the authority associated with key U.
6) /sbin/request-key execs an appropriate program to perform the actual
instantiation.
7) The program may want to access another key from A's context (say a
Kerberos TGT key). It just requests the appropriate key, and the keyring
search notes that the session keyring has auth key V in its bottom level.
This will permit it to then search the keyrings of process A with the
UID, GID, groups and security info of process A as if it was process A,
and come up with key W.
8) The program then does what it must to get the data with which to
instantiate key U, using key W as a reference (perhaps it contacts a
Kerberos server using the TGT) and then instantiates key U.
9) Upon instantiating key U, auth key V is automatically revoked so that it
may not be used again.
10) The program then exits 0 and request_key() deletes key V and returns key
U to the caller.
This also extends further. If key W (step 7 above) didn't exist, key W would
be created uninstantiated, another auth key (X) would be created (as per step
3) and another copy of /sbin/request-key spawned (as per step 4); but the
context specified by auth key X will still be process A, as it was in auth key
V.
This is because process A's keyrings can't simply be attached to
/sbin/request-key at the appropriate places because (a) execve will discard two
of them, and (b) it requires the same UID/GID/Groups all the way through.
Negative Instantiation And Rejection
====================================
Rather than instantiating a key, it is possible for the possessor of an
authorisation key to negatively instantiate a key that's under construction.
This is a short duration placeholder that causes any attempt at re-requesting
the key while it exists to fail with error ENOKEY if negated or the specified
error if rejected.
This is provided to prevent excessive repeated spawning of /sbin/request-key
processes for a key that will never be obtainable.
Should the /sbin/request-key process exit anything other than 0 or die on a
signal, the key under construction will be automatically negatively
instantiated for a short amount of time.
The Search Algorithm
====================
A search of any particular keyring proceeds in the following fashion:
1) When the key management code searches for a key (keyring_search_rcu) it
firstly calls key_permission(SEARCH) on the keyring it's starting with,
if this denies permission, it doesn't search further.
2) It considers all the non-keyring keys within that keyring and, if any key
matches the criteria specified, calls key_permission(SEARCH) on it to see
if the key is allowed to be found. If it is, that key is returned; if
not, the search continues, and the error code is retained if of higher
priority than the one currently set.
3) It then considers all the keyring-type keys in the keyring it's currently
searching. It calls key_permission(SEARCH) on each keyring, and if this
grants permission, it recurses, executing steps (2) and (3) on that
keyring.
The process stops immediately a valid key is found with permission granted to
use it. Any error from a previous match attempt is discarded and the key is
returned.
When request_key() is invoked, if CONFIG_KEYS_REQUEST_CACHE=y, a per-task
one-key cache is first checked for a match.
When search_process_keyrings() is invoked, it performs the following searches
until one succeeds:
1) If extant, the process's thread keyring is searched.
2) If extant, the process's process keyring is searched.
3) The process's session keyring is searched.
4) If the process has assumed the authority associated with a request_key()
authorisation key then:
a) If extant, the calling process's thread keyring is searched.
b) If extant, the calling process's process keyring is searched.
c) The calling process's session keyring is searched.
The moment one succeeds, all pending errors are discarded and the found key is
returned. If CONFIG_KEYS_REQUEST_CACHE=y, then that key is placed in the
per-task cache, displacing the previous key. The cache is cleared on exit or
just prior to resumption of userspace.
Only if all these fail does the whole thing fail with the highest priority
error. Note that several errors may have come from LSM.
The error priority is::
EKEYREVOKED > EKEYEXPIRED > ENOKEY
EACCES/EPERM are only returned on a direct search of a specific keyring where
the basal keyring does not grant Search permission.
linux-7.2.3/Documentation/security/keys/trusted-encrypted.rst
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==========================
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.
Trusted Keys as Protected key
=============================
It is the secure way of keeping the keys in the kernel key-ring as Trusted-Key,
such that:
- Key-blob, an encrypted key-data, created to be stored, loaded and seen by
userspace.
- Key-data, the plain-key text in the system memory, to be used by
kernel space only.
Though key-data is not accessible to the user-space in plain-text, but it is in
plain-text in system memory, when used in kernel space. Even though kernel-space
attracts small surface attack, but with compromised kernel or side-channel
attack accessing the system memory can lead to a chance of the key getting
compromised/leaked.
In order to protect the key in kernel space, the concept of "protected-keys" is
introduced which will act as an added layer of protection. The key-data of the
protected keys is encrypted with Key-Encryption-Key(KEK), and decrypted inside
the trust source boundary. The plain-key text never available out-side in the
system memory. Thus, any crypto operation that is to be executed using the
protected key, can only be done by the trust source, which generated the
key blob.
Hence, if the protected-key is leaked or compromised, it is of no use to the
hacker.
Trusted keys as protected keys, with trust source having the capability of
generating:
- Key-Blob, to be loaded, stored and seen by user-space.
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).
(5) PKWM (PowerVM Key Wrapping Module: IBM PowerVM + Platform KeyStore)
Rooted to a unique, per-LPAR key, which is derived from a system-wide,
randomly generated LPAR root key. Both the per-LPAR keys and the LPAR
root key are stored in hypervisor-owned secure memory at runtime,
and the LPAR root key is additionally persisted in secure locations
such as the processor SEEPROMs and encrypted NVRAM.
* 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.
(5) PKWM (PowerVM Key Wrapping Module: IBM PowerVM + Platform KeyStore)
Fixed set of cryptographic operations done on on-chip hardware
cryptographic acceleration unit NX. Keys for wrapping and unwrapping
are managed by PowerVM Platform KeyStore, which stores keys in an
isolated in-memory copy in secure hypervisor memory, as well as in a
persistent copy in hypervisor-encrypted NVRAM.
* 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.
(5) PKWM (PowerVM Key Wrapping Module: IBM PowerVM + Platform KeyStore)
Relies on secure and trusted boot process of IBM Power systems 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``.
(5) PKWM (PowerVM Key Wrapping Module: IBM PowerVM + Platform KeyStore)
Platform Keystore has well documented interfaces in PAPR document.
Refer to ``Documentation/arch/powerpc/papr_hcalls.rst``
* 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.
* PKWM (PowerVM Key Wrapping Module: IBM PowerVM + Platform KeyStore)
The normal kernel random number generator is used to generate keys.
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
------------------------
Trusted Keys 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 as Protected Keys Usage::
keyctl add trusted name "new keylen pk [options]" ring
keyctl add trusted name "load hex_blob [options]" ring
keyctl print keyid
where, 'pk' is used to direct trust source to generate protected key.
options:
key_enc_algo = For CAAM, supported enc algo are ECB(2), CCM(1).
"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).
Trusted Keys usage: PKWM
------------------------
Usage::
keyctl add trusted name "new keylen [options]" ring
keyctl add trusted name "load hex_blob" ring
keyctl print keyid
options:
wrap_flags= ascii hex value of security policy requirement
0x00: no secure boot requirement (default)
0x01: require secure boot to be in either audit or
enforced mode
0x02: require secure boot to be in enforced mode
"keyctl print" returns an ASCII hex copy of the sealed key, which is in format
specific to PKWM 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
Create and save a trusted key as protected key named "kmk" of length 32 bytes.
::
$ keyctl add trusted kmk "new 32 pk key_enc_algo=1" @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` key_enc_algo=1" @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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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