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1==========================2Trusted and Encrypted Keys3==========================4 5Trusted and Encrypted Keys are two new key types added to the existing kernel6key ring service. Both of these new types are variable length symmetric keys,7and in both cases all keys are created in the kernel, and user space sees,8stores, and loads only encrypted blobs. Trusted Keys require the availability9of a Trust Source for greater security, while Encrypted Keys can be used on any10system. All user level blobs, are displayed and loaded in hex ASCII for11convenience, and are integrity verified.12 13 14Trust Source15============16 17A trust source provides the source of security for Trusted Keys. This18section lists currently supported trust sources, along with their security19considerations. Whether or not a trust source is sufficiently safe depends20on the strength and correctness of its implementation, as well as the threat21environment for a specific use case. Since the kernel doesn't know what the22environment is, and there is no metric of trust, it is dependent on the23consumer of the Trusted Keys to determine if the trust source is sufficiently24safe.25 26 * Root of trust for storage27 28 (1) TPM (Trusted Platform Module: hardware device)29 30 Rooted to Storage Root Key (SRK) which never leaves the TPM that31 provides crypto operation to establish root of trust for storage.32 33 (2) TEE (Trusted Execution Environment: OP-TEE based on Arm TrustZone)34 35 Rooted to Hardware Unique Key (HUK) which is generally burnt in on-chip36 fuses and is accessible to TEE only.37 38 (3) CAAM (Cryptographic Acceleration and Assurance Module: IP on NXP SoCs)39 40 When High Assurance Boot (HAB) is enabled and the CAAM is in secure41 mode, trust is rooted to the OTPMK, a never-disclosed 256-bit key42 randomly generated and fused into each SoC at manufacturing time.43 Otherwise, a common fixed test key is used instead.44 45 (4) DCP (Data Co-Processor: crypto accelerator of various i.MX SoCs)46 47 Rooted to a one-time programmable key (OTP) that is generally burnt48 in the on-chip fuses and is accessible to the DCP encryption engine only.49 DCP provides two keys that can be used as root of trust: the OTP key50 and the UNIQUE key. Default is to use the UNIQUE key, but selecting51 the OTP key can be done via a module parameter (dcp_use_otp_key).52 53 * Execution isolation54 55 (1) TPM56 57 Fixed set of operations running in isolated execution environment.58 59 (2) TEE60 61 Customizable set of operations running in isolated execution62 environment verified via Secure/Trusted boot process.63 64 (3) CAAM65 66 Fixed set of operations running in isolated execution environment.67 68 (4) DCP69 70 Fixed set of cryptographic operations running in isolated execution71 environment. Only basic blob key encryption is executed there.72 The actual key sealing/unsealing is done on main processor/kernel space.73 74 * Optional binding to platform integrity state75 76 (1) TPM77 78 Keys can be optionally sealed to specified PCR (integrity measurement)79 values, and only unsealed by the TPM, if PCRs and blob integrity80 verifications match. A loaded Trusted Key can be updated with new81 (future) PCR values, so keys are easily migrated to new PCR values,82 such as when the kernel and initramfs are updated. The same key can83 have many saved blobs under different PCR values, so multiple boots are84 easily supported.85 86 (2) TEE87 88 Relies on Secure/Trusted boot process for platform integrity. It can89 be extended with TEE based measured boot process.90 91 (3) CAAM92 93 Relies on the High Assurance Boot (HAB) mechanism of NXP SoCs94 for platform integrity.95 96 (4) DCP97 98 Relies on Secure/Trusted boot process (called HAB by vendor) for99 platform integrity.100 101 * Interfaces and APIs102 103 (1) TPM104 105 TPMs have well-documented, standardized interfaces and APIs.106 107 (2) TEE108 109 TEEs have well-documented, standardized client interface and APIs. For110 more details refer to ``Documentation/driver-api/tee.rst``.111 112 (3) CAAM113 114 Interface is specific to silicon vendor.115 116 (4) DCP117 118 Vendor-specific API that is implemented as part of the DCP crypto driver in119 ``drivers/crypto/mxs-dcp.c``.120 121 * Threat model122 123 The strength and appropriateness of a particular trust source for a given124 purpose must be assessed when using them to protect security-relevant data.125 126 127Key Generation128==============129 130Trusted Keys131------------132 133New keys are created from random numbers. They are encrypted/decrypted using134a child key in the storage key hierarchy. Encryption and decryption of the135child key must be protected by a strong access control policy within the136trust source. The random number generator in use differs according to the137selected trust source:138 139 * TPM: hardware device based RNG140 141 Keys are generated within the TPM. Strength of random numbers may vary142 from one device manufacturer to another.143 144 * TEE: OP-TEE based on Arm TrustZone based RNG145 146 RNG is customizable as per platform needs. It can either be direct output147 from platform specific hardware RNG or a software based Fortuna CSPRNG148 which can be seeded via multiple entropy sources.149 150 * CAAM: Kernel RNG151 152 The normal kernel random number generator is used. To seed it from the153 CAAM HWRNG, enable CRYPTO_DEV_FSL_CAAM_RNG_API and ensure the device154 is probed.155 156 * DCP (Data Co-Processor: crypto accelerator of various i.MX SoCs)157 158 The DCP hardware device itself does not provide a dedicated RNG interface,159 so the kernel default RNG is used. SoCs with DCP like the i.MX6ULL do have160 a dedicated hardware RNG that is independent from DCP which can be enabled161 to back the kernel RNG.162 163Users may override this by specifying ``trusted.rng=kernel`` on the kernel164command-line to override the used RNG with the kernel's random number pool.165 166Encrypted Keys167--------------168 169Encrypted keys do not depend on a trust source, and are faster, as they use AES170for encryption/decryption. New keys are created either from kernel-generated171random numbers or user-provided decrypted data, and are encrypted/decrypted172using a specified ‘master’ key. The ‘master’ key can either be a trusted-key or173user-key type. The main disadvantage of encrypted keys is that if they are not174rooted in a trusted key, they are only as secure as the user key encrypting175them. The master user key should therefore be loaded in as secure a way as176possible, preferably early in boot.177 178 179Usage180=====181 182Trusted Keys usage: TPM183-----------------------184 185TPM 1.2: By default, trusted keys are sealed under the SRK, which has the186default authorization value (20 bytes of 0s). This can be set at takeownership187time with the TrouSerS utility: "tpm_takeownership -u -z".188 189TPM 2.0: The user must first create a storage key and make it persistent, so the190key is available after reboot. This can be done using the following commands.191 192With the IBM TSS 2 stack::193 194 #> tsscreateprimary -hi o -st195 Handle 80000000196 #> tssevictcontrol -hi o -ho 80000000 -hp 81000001197 198Or with the Intel TSS 2 stack::199 200 #> tpm2_createprimary --hierarchy o -G rsa2048 -c key.ctxt201 [...]202 #> tpm2_evictcontrol -c key.ctxt 0x81000001203 persistentHandle: 0x81000001204 205Usage::206 207 keyctl add trusted name "new keylen [options]" ring208 keyctl add trusted name "load hex_blob [pcrlock=pcrnum]" ring209 keyctl update key "update [options]"210 keyctl print keyid211 212 options:213 keyhandle= ascii hex value of sealing key214 TPM 1.2: default 0x40000000 (SRK)215 TPM 2.0: no default; must be passed every time216 keyauth= ascii hex auth for sealing key default 0x00...i217 (40 ascii zeros)218 blobauth= ascii hex auth for sealed data default 0x00...219 (40 ascii zeros)220 pcrinfo= ascii hex of PCR_INFO or PCR_INFO_LONG (no default)221 pcrlock= pcr number to be extended to "lock" blob222 migratable= 0|1 indicating permission to reseal to new PCR values,223 default 1 (resealing allowed)224 hash= hash algorithm name as a string. For TPM 1.x the only225 allowed value is sha1. For TPM 2.x the allowed values226 are sha1, sha256, sha384, sha512 and sm3-256.227 policydigest= digest for the authorization policy. must be calculated228 with the same hash algorithm as specified by the 'hash='229 option.230 policyhandle= handle to an authorization policy session that defines the231 same policy and with the same hash algorithm as was used to232 seal the key.233 234"keyctl print" returns an ascii hex copy of the sealed key, which is in standard235TPM_STORED_DATA format. The key length for new keys are always in bytes.236Trusted Keys can be 32 - 128 bytes (256 - 1024 bits), the upper limit is to fit237within the 2048 bit SRK (RSA) keylength, with all necessary structure/padding.238 239Trusted Keys usage: TEE240-----------------------241 242Usage::243 244 keyctl add trusted name "new keylen" ring245 keyctl add trusted name "load hex_blob" ring246 keyctl print keyid247 248"keyctl print" returns an ASCII hex copy of the sealed key, which is in format249specific to TEE device implementation. The key length for new keys is always250in bytes. Trusted Keys can be 32 - 128 bytes (256 - 1024 bits).251 252Trusted Keys usage: CAAM253------------------------254 255Usage::256 257 keyctl add trusted name "new keylen" ring258 keyctl add trusted name "load hex_blob" ring259 keyctl print keyid260 261"keyctl print" returns an ASCII hex copy of the sealed key, which is in a262CAAM-specific format. The key length for new keys is always in bytes.263Trusted Keys can be 32 - 128 bytes (256 - 1024 bits).264 265Trusted Keys usage: DCP266-----------------------267 268Usage::269 270 keyctl add trusted name "new keylen" ring271 keyctl add trusted name "load hex_blob" ring272 keyctl print keyid273 274"keyctl print" returns an ASCII hex copy of the sealed key, which is in format275specific to this DCP key-blob implementation. The key length for new keys is276always in bytes. Trusted Keys can be 32 - 128 bytes (256 - 1024 bits).277 278Encrypted Keys usage279--------------------280 281The decrypted portion of encrypted keys can contain either a simple symmetric282key or a more complex structure. The format of the more complex structure is283application specific, which is identified by 'format'.284 285Usage::286 287 keyctl add encrypted name "new [format] key-type:master-key-name keylen"288 ring289 keyctl add encrypted name "new [format] key-type:master-key-name keylen290 decrypted-data" ring291 keyctl add encrypted name "load hex_blob" ring292 keyctl update keyid "update key-type:master-key-name"293 294Where::295 296 format:= 'default | ecryptfs | enc32'297 key-type:= 'trusted' | 'user'298 299Examples of trusted and encrypted key usage300-------------------------------------------301 302Create and save a trusted key named "kmk" of length 32 bytes.303 304Note: When using a TPM 2.0 with a persistent key with handle 0x81000001,305append 'keyhandle=0x81000001' to statements between quotes, such as306"new 32 keyhandle=0x81000001".307 308::309 310 $ keyctl add trusted kmk "new 32" @u311 440502848312 313 $ keyctl show314 Session Keyring315 -3 --alswrv 500 500 keyring: _ses316 97833714 --alswrv 500 -1 \_ keyring: _uid.500317 440502848 --alswrv 500 500 \_ trusted: kmk318 319 $ keyctl print 440502848320 0101000000000000000001005d01b7e3f4a6be5709930f3b70a743cbb42e0cc95e18e915321 3f60da455bbf1144ad12e4f92b452f966929f6105fd29ca28e4d4d5a031d068478bacb0b322 27351119f822911b0a11ba3d3498ba6a32e50dac7f32894dd890eb9ad578e4e292c83722323 a52e56a097e6a68b3f56f7a52ece0cdccba1eb62cad7d817f6dc58898b3ac15f36026fec324 d568bd4a706cb60bb37be6d8f1240661199d640b66fb0fe3b079f97f450b9ef9c22c6d5d325 dd379f0facd1cd020281dfa3c70ba21a3fa6fc2471dc6d13ecf8298b946f65345faa5ef0326 f1f8fff03ad0acb083725535636addb08d73dedb9832da198081e5deae84bfaf0409c22b327 e4a8aea2b607ec96931e6f4d4fe563ba328 329 $ keyctl pipe 440502848 > kmk.blob330 331Load a trusted key from the saved blob::332 333 $ keyctl add trusted kmk "load `cat kmk.blob`" @u334 268728824335 336 $ keyctl print 268728824337 0101000000000000000001005d01b7e3f4a6be5709930f3b70a743cbb42e0cc95e18e915338 3f60da455bbf1144ad12e4f92b452f966929f6105fd29ca28e4d4d5a031d068478bacb0b339 27351119f822911b0a11ba3d3498ba6a32e50dac7f32894dd890eb9ad578e4e292c83722340 a52e56a097e6a68b3f56f7a52ece0cdccba1eb62cad7d817f6dc58898b3ac15f36026fec341 d568bd4a706cb60bb37be6d8f1240661199d640b66fb0fe3b079f97f450b9ef9c22c6d5d342 dd379f0facd1cd020281dfa3c70ba21a3fa6fc2471dc6d13ecf8298b946f65345faa5ef0343 f1f8fff03ad0acb083725535636addb08d73dedb9832da198081e5deae84bfaf0409c22b344 e4a8aea2b607ec96931e6f4d4fe563ba345 346Reseal (TPM specific) a trusted key under new PCR values::347 348 $ keyctl update 268728824 "update pcrinfo=`cat pcr.blob`"349 $ keyctl print 268728824350 010100000000002c0002800093c35a09b70fff26e7a98ae786c641e678ec6ffb6b46d805351 77c8a6377aed9d3219c6dfec4b23ffe3000001005d37d472ac8a44023fbb3d18583a4f73352 d3a076c0858f6f1dcaa39ea0f119911ff03f5406df4f7f27f41da8d7194f45c9f4e00f2e353 df449f266253aa3f52e55c53de147773e00f0f9aca86c64d94c95382265968c354c5eab4354 9638c5ae99c89de1e0997242edfb0b501744e11ff9762dfd951cffd93227cc513384e7e6355 e782c29435c7ec2edafaa2f4c1fe6e7a781b59549ff5296371b42133777dcc5b8b971610356 94bc67ede19e43ddb9dc2baacad374a36feaf0314d700af0a65c164b7082401740e489c9357 7ef6a24defe4846104209bf0c3eced7fa1a672ed5b125fc9d8cd88b476a658a4434644ef358 df8ae9a178e9f83ba9f08d10fa47e4226b98b0702f06b3b8359 360 361The initial consumer of trusted keys is EVM, which at boot time needs a high362quality symmetric key for HMAC protection of file metadata. The use of a363trusted key provides strong guarantees that the EVM key has not been364compromised by a user level problem, and when sealed to a platform integrity365state, protects against boot and offline attacks. Create and save an366encrypted key "evm" using the above trusted key "kmk":367 368option 1: omitting 'format'::369 370 $ keyctl add encrypted evm "new trusted:kmk 32" @u371 159771175372 373option 2: explicitly defining 'format' as 'default'::374 375 $ keyctl add encrypted evm "new default trusted:kmk 32" @u376 159771175377 378 $ keyctl print 159771175379 default trusted:kmk 32 2375725ad57798846a9bbd240de8906f006e66c03af53b1b3380 82dbbc55be2a44616e4959430436dc4f2a7a9659aa60bb4652aeb2120f149ed197c564e0381 24717c64 5972dcb82ab2dde83376d82b2e3c09ffc382 383 $ keyctl pipe 159771175 > evm.blob384 385Load an encrypted key "evm" from saved blob::386 387 $ keyctl add encrypted evm "load `cat evm.blob`" @u388 831684262389 390 $ keyctl print 831684262391 default trusted:kmk 32 2375725ad57798846a9bbd240de8906f006e66c03af53b1b3392 82dbbc55be2a44616e4959430436dc4f2a7a9659aa60bb4652aeb2120f149ed197c564e0393 24717c64 5972dcb82ab2dde83376d82b2e3c09ffc394 395Instantiate an encrypted key "evm" using user-provided decrypted data::396 397 $ evmkey=$(dd if=/dev/urandom bs=1 count=32 | xxd -c32 -p)398 $ keyctl add encrypted evm "new default user:kmk 32 $evmkey" @u399 794890253400 401 $ keyctl print 794890253402 default user:kmk 32 2375725ad57798846a9bbd240de8906f006e66c03af53b1b382d403 bbc55be2a44616e4959430436dc4f2a7a9659aa60bb4652aeb2120f149ed197c564e0247404 17c64 5972dcb82ab2dde83376d82b2e3c09ffc405 406Other uses for trusted and encrypted keys, such as for disk and file encryption407are anticipated. In particular the new format 'ecryptfs' has been defined408in order to use encrypted keys to mount an eCryptfs filesystem. More details409about the usage can be found in the file410``Documentation/security/keys/ecryptfs.rst``.411 412Another new format 'enc32' has been defined in order to support encrypted keys413with payload size of 32 bytes. This will initially be used for nvdimm security414but may expand to other usages that require 32 bytes payload.415 416 417TPM 2.0 ASN.1 Key Format418------------------------419 420The TPM 2.0 ASN.1 key format is designed to be easily recognisable,421even in binary form (fixing a problem we had with the TPM 1.2 ASN.1422format) and to be extensible for additions like importable keys and423policy::424 425 TPMKey ::= SEQUENCE {426 type OBJECT IDENTIFIER427 emptyAuth [0] EXPLICIT BOOLEAN OPTIONAL428 parent INTEGER429 pubkey OCTET STRING430 privkey OCTET STRING431 }432 433type is what distinguishes the key even in binary form since the OID434is provided by the TCG to be unique and thus forms a recognizable435binary pattern at offset 3 in the key. The OIDs currently made436available are::437 438 2.23.133.10.1.3 TPM Loadable key. This is an asymmetric key (Usually439 RSA2048 or Elliptic Curve) which can be imported by a440 TPM2_Load() operation.441 442 2.23.133.10.1.4 TPM Importable Key. This is an asymmetric key (Usually443 RSA2048 or Elliptic Curve) which can be imported by a444 TPM2_Import() operation.445 446 2.23.133.10.1.5 TPM Sealed Data. This is a set of data (up to 128447 bytes) which is sealed by the TPM. It usually448 represents a symmetric key and must be unsealed before449 use.450 451The trusted key code only uses the TPM Sealed Data OID.452 453emptyAuth is true if the key has well known authorization "". If it454is false or not present, the key requires an explicit authorization455phrase. This is used by most user space consumers to decide whether456to prompt for a password.457 458parent represents the parent key handle, either in the 0x81 MSO space,459like 0x81000001 for the RSA primary storage key. Userspace programmes460also support specifying the primary handle in the 0x40 MSO space. If461this happens the Elliptic Curve variant of the primary key using the462TCG defined template will be generated on the fly into a volatile463object and used as the parent. The current kernel code only supports464the 0x81 MSO form.465 466pubkey is the binary representation of TPM2B_PRIVATE excluding the467initial TPM2B header, which can be reconstructed from the ASN.1 octet468string length.469 470privkey is the binary representation of TPM2B_PUBLIC excluding the471initial TPM2B header which can be reconstructed from the ASN.1 octed472string length.473 474DCP Blob Format475---------------476 477.. kernel-doc:: security/keys/trusted-keys/trusted_dcp.c478 :doc: dcp blob format479 480.. kernel-doc:: security/keys/trusted-keys/trusted_dcp.c481 :identifiers: struct dcp_blob_fmt482