signature.txt 22 KB

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  1. U-Boot FIT Signature Verification
  2. =================================
  3. Introduction
  4. ------------
  5. FIT supports hashing of images so that these hashes can be checked on
  6. loading. This protects against corruption of the image. However it does not
  7. prevent the substitution of one image for another.
  8. The signature feature allows the hash to be signed with a private key such
  9. that it can be verified using a public key later. Provided that the private
  10. key is kept secret and the public key is stored in a non-volatile place,
  11. any image can be verified in this way.
  12. See verified-boot.txt for more general information on verified boot.
  13. Concepts
  14. --------
  15. Some familiarity with public key cryptography is assumed in this section.
  16. The procedure for signing is as follows:
  17. - hash an image in the FIT
  18. - sign the hash with a private key to produce a signature
  19. - store the resulting signature in the FIT
  20. The procedure for verification is:
  21. - read the FIT
  22. - obtain the public key
  23. - extract the signature from the FIT
  24. - hash the image from the FIT
  25. - verify (with the public key) that the extracted signature matches the
  26. hash
  27. The signing is generally performed by mkimage, as part of making a firmware
  28. image for the device. The verification is normally done in U-Boot on the
  29. device.
  30. Algorithms
  31. ----------
  32. In principle any suitable algorithm can be used to sign and verify a hash.
  33. At present only one class of algorithms is supported: SHA1 hashing with RSA.
  34. This works by hashing the image to produce a 20-byte hash.
  35. While it is acceptable to bring in large cryptographic libraries such as
  36. openssl on the host side (e.g. mkimage), it is not desirable for U-Boot.
  37. For the run-time verification side, it is important to keep code and data
  38. size as small as possible.
  39. For this reason the RSA image verification uses pre-processed public keys
  40. which can be used with a very small amount of code - just some extraction
  41. of data from the FDT and exponentiation mod n. Code size impact is a little
  42. under 5KB on Tegra Seaboard, for example.
  43. It is relatively straightforward to add new algorithms if required. If
  44. another RSA variant is needed, then it can be added to the table in
  45. image-sig.c. If another algorithm is needed (such as DSA) then it can be
  46. placed alongside rsa.c, and its functions added to the table in image-sig.c
  47. also.
  48. Creating an RSA key pair and certificate
  49. ----------------------------------------
  50. To create a new public/private key pair, size 2048 bits:
  51. $ openssl genpkey -algorithm RSA -out keys/dev.key \
  52. -pkeyopt rsa_keygen_bits:2048 -pkeyopt rsa_keygen_pubexp:65537
  53. To create a certificate for this containing the public key:
  54. $ openssl req -batch -new -x509 -key keys/dev.key -out keys/dev.crt
  55. If you like you can look at the public key also:
  56. $ openssl rsa -in keys/dev.key -pubout
  57. Device Tree Bindings
  58. --------------------
  59. The following properties are required in the FIT's signature node(s) to
  60. allow the signer to operate. These should be added to the .its file.
  61. Signature nodes sit at the same level as hash nodes and are called
  62. signature-1, signature-2, etc.
  63. - algo: Algorithm name (e.g. "sha1,rsa2048")
  64. - key-name-hint: Name of key to use for signing. The keys will normally be in
  65. a single directory (parameter -k to mkimage). For a given key <name>, its
  66. private key is stored in <name>.key and the certificate is stored in
  67. <name>.crt.
  68. When the image is signed, the following properties are added (mandatory):
  69. - value: The signature data (e.g. 256 bytes for 2048-bit RSA)
  70. When the image is signed, the following properties are optional:
  71. - timestamp: Time when image was signed (standard Unix time_t format)
  72. - signer-name: Name of the signer (e.g. "mkimage")
  73. - signer-version: Version string of the signer (e.g. "2013.01")
  74. - comment: Additional information about the signer or image
  75. - padding: The padding algorithm, it may be pkcs-1.5 or pss,
  76. if no value is provided we assume pkcs-1.5
  77. For config bindings (see Signed Configurations below), the following
  78. additional properties are optional:
  79. - sign-images: A list of images to sign, each being a property of the conf
  80. node that contains then. The default is "kernel,fdt" which means that these
  81. two images will be looked up in the config and signed if present.
  82. For config bindings, these properties are added by the signer:
  83. - hashed-nodes: A list of nodes which were hashed by the signer. Each is
  84. a string - the full path to node. A typical value might be:
  85. hashed-nodes = "/", "/configurations/conf-1", "/images/kernel",
  86. "/images/kernel/hash-1", "/images/fdt-1",
  87. "/images/fdt-1/hash-1";
  88. - hashed-strings: The start and size of the string region of the FIT that
  89. was hashed
  90. Example: See sign-images.its for an example image tree source file and
  91. sign-configs.its for config signing.
  92. Public Key Storage
  93. ------------------
  94. In order to verify an image that has been signed with a public key we need to
  95. have a trusted public key. This cannot be stored in the signed image, since
  96. it would be easy to alter. For this implementation we choose to store the
  97. public key in U-Boot's control FDT (using CONFIG_OF_CONTROL).
  98. Public keys should be stored as sub-nodes in a /signature node. Required
  99. properties are:
  100. - algo: Algorithm name (e.g. "sha1,rsa2048" or "sha256,ecdsa256")
  101. Optional properties are:
  102. - key-name-hint: Name of key used for signing. This is only a hint since it
  103. is possible for the name to be changed. Verification can proceed by checking
  104. all available signing keys until one matches.
  105. - required: If present this indicates that the key must be verified for the
  106. image / configuration to be considered valid. Only required keys are
  107. normally verified by the FIT image booting algorithm. Valid values are
  108. "image" to force verification of all images, and "conf" to force verification
  109. of the selected configuration (which then relies on hashes in the images to
  110. verify those).
  111. Each signing algorithm has its own additional properties.
  112. For RSA the following are mandatory:
  113. - rsa,num-bits: Number of key bits (e.g. 2048)
  114. - rsa,modulus: Modulus (N) as a big-endian multi-word integer
  115. - rsa,exponent: Public exponent (E) as a 64 bit unsigned integer
  116. - rsa,r-squared: (2^num-bits)^2 as a big-endian multi-word integer
  117. - rsa,n0-inverse: -1 / modulus[0] mod 2^32
  118. For ECDSA the following are mandatory:
  119. - ecdsa,curve: Name of ECDSA curve (e.g. "prime256v1")
  120. - ecdsa,x-point: Public key X coordinate as a big-endian multi-word integer
  121. - ecdsa,y-point: Public key Y coordinate as a big-endian multi-word integer
  122. These parameters can be added to a binary device tree using parameter -K of the
  123. mkimage command::
  124. tools/mkimage -f fit.its -K control.dtb -k keys -r image.fit
  125. Here is an example of a generated device tree node::
  126. signature {
  127. key-dev {
  128. required = "conf";
  129. algo = "sha256,rsa2048";
  130. rsa,r-squared = <0xb76d1acf 0xa1763ca5 0xeb2f126
  131. 0x742edc80 0xd3f42177 0x9741d9d9
  132. 0x35bb476e 0xff41c718 0xd3801430
  133. 0xf22537cb 0xa7e79960 0xae32a043
  134. 0x7da1427a 0x341d6492 0x3c2762f5
  135. 0xaac04726 0x5b262d96 0xf984e86d
  136. 0xb99443c7 0x17080c33 0x940f6892
  137. 0xd57a95d1 0x6ea7b691 0xc5038fa8
  138. 0x6bb48a6e 0x73f1b1ea 0x37160841
  139. 0xe05715ce 0xa7c45bbd 0x690d82d5
  140. 0x99c2454c 0x6ff117b3 0xd830683b
  141. 0x3f81c9cf 0x1ca38a91 0x0c3392e4
  142. 0xd817c625 0x7b8e9a24 0x175b89ea
  143. 0xad79f3dc 0x4d50d7b4 0x9d4e90f8
  144. 0xad9e2939 0xc165d6a4 0x0ada7e1b
  145. 0xfb1bf495 0xfc3131c2 0xb8c6e604
  146. 0xc2761124 0xf63de4a6 0x0e9565f9
  147. 0xc8e53761 0x7e7a37a5 0xe99dcdae
  148. 0x9aff7e1e 0xbd44b13d 0x6b0e6aa4
  149. 0x038907e4 0x8e0d6850 0xef51bc20
  150. 0xf73c94af 0x88bea7b1 0xcbbb1b30
  151. 0xd024b7f3>;
  152. rsa,modulus = <0xc0711d6cb 0x9e86db7f 0x45986dbe
  153. 0x023f1e8c9 0xe1a4c4d0 0x8a0dfdc9
  154. 0x023ba0c48 0x06815f6a 0x5caa0654
  155. 0x07078c4b7 0x3d154853 0x40729023
  156. 0x0b007c8fe 0x5a3647e5 0x23b41e20
  157. 0x024720591 0x66915305 0x0e0b29b0
  158. 0x0de2ad30d 0x8589430f 0xb1590325
  159. 0x0fb9f5d5e 0x9eba752a 0xd88e6de9
  160. 0x056b3dcc6 0x9a6b8e61 0x6784f61f
  161. 0x000f39c21 0x5eec6b33 0xd78e4f78
  162. 0x0921a305f 0xaa2cc27e 0x1ca917af
  163. 0x06e1134f4 0xd48cac77 0x4e914d07
  164. 0x0f707aa5a 0x0d141f41 0x84677f1d
  165. 0x0ad47a049 0x028aedb6 0xd5536fcf
  166. 0x03fef1e4f 0x133a03d2 0xfd7a750a
  167. 0x0f9159732 0xd207812e 0x6a807375
  168. 0x06434230d 0xc8e22dad 0x9f29b3d6
  169. 0x07c44ac2b 0xfa2aad88 0xe2429504
  170. 0x041febd41 0x85d0d142 0x7b194d65
  171. 0x06e5d55ea 0x41116961 0xf3181dde
  172. 0x068bf5fbc 0x3dd82047 0x00ee647e
  173. 0x0d7a44ab3>;
  174. rsa,exponent = <0x00 0x10001>;
  175. rsa,n0-inverse = <0xb3928b85>;
  176. rsa,num-bits = <0x800>;
  177. key-name-hint = "dev";
  178. };
  179. };
  180. Signed Configurations
  181. ---------------------
  182. While signing images is useful, it does not provide complete protection
  183. against several types of attack. For example, it it possible to create a
  184. FIT with the same signed images, but with the configuration changed such
  185. that a different one is selected (mix and match attack). It is also possible
  186. to substitute a signed image from an older FIT version into a newer FIT
  187. (roll-back attack).
  188. As an example, consider this FIT:
  189. / {
  190. images {
  191. kernel-1 {
  192. data = <data for kernel1>
  193. signature-1 {
  194. algo = "sha1,rsa2048";
  195. value = <...kernel signature 1...>
  196. };
  197. };
  198. kernel-2 {
  199. data = <data for kernel2>
  200. signature-1 {
  201. algo = "sha1,rsa2048";
  202. value = <...kernel signature 2...>
  203. };
  204. };
  205. fdt-1 {
  206. data = <data for fdt1>;
  207. signature-1 {
  208. algo = "sha1,rsa2048";
  209. value = <...fdt signature 1...>
  210. };
  211. };
  212. fdt-2 {
  213. data = <data for fdt2>;
  214. signature-1 {
  215. algo = "sha1,rsa2048";
  216. value = <...fdt signature 2...>
  217. };
  218. };
  219. };
  220. configurations {
  221. default = "conf-1";
  222. conf-1 {
  223. kernel = "kernel-1";
  224. fdt = "fdt-1";
  225. };
  226. conf-2 {
  227. kernel = "kernel-2";
  228. fdt = "fdt-2";
  229. };
  230. };
  231. };
  232. Since both kernels are signed it is easy for an attacker to add a new
  233. configuration 3 with kernel 1 and fdt 2:
  234. configurations {
  235. default = "conf-1";
  236. conf-1 {
  237. kernel = "kernel-1";
  238. fdt = "fdt-1";
  239. };
  240. conf-2 {
  241. kernel = "kernel-2";
  242. fdt = "fdt-2";
  243. };
  244. conf-3 {
  245. kernel = "kernel-1";
  246. fdt = "fdt-2";
  247. };
  248. };
  249. With signed images, nothing protects against this. Whether it gains an
  250. advantage for the attacker is debatable, but it is not secure.
  251. To solve this problem, we support signed configurations. In this case it
  252. is the configurations that are signed, not the image. Each image has its
  253. own hash, and we include the hash in the configuration signature.
  254. So the above example is adjusted to look like this:
  255. / {
  256. images {
  257. kernel-1 {
  258. data = <data for kernel1>
  259. hash-1 {
  260. algo = "sha1";
  261. value = <...kernel hash 1...>
  262. };
  263. };
  264. kernel-2 {
  265. data = <data for kernel2>
  266. hash-1 {
  267. algo = "sha1";
  268. value = <...kernel hash 2...>
  269. };
  270. };
  271. fdt-1 {
  272. data = <data for fdt1>;
  273. hash-1 {
  274. algo = "sha1";
  275. value = <...fdt hash 1...>
  276. };
  277. };
  278. fdt-2 {
  279. data = <data for fdt2>;
  280. hash-1 {
  281. algo = "sha1";
  282. value = <...fdt hash 2...>
  283. };
  284. };
  285. };
  286. configurations {
  287. default = "conf-1";
  288. conf-1 {
  289. kernel = "kernel-1";
  290. fdt = "fdt-1";
  291. signature-1 {
  292. algo = "sha1,rsa2048";
  293. value = <...conf 1 signature...>;
  294. };
  295. };
  296. conf-2 {
  297. kernel = "kernel-2";
  298. fdt = "fdt-2";
  299. signature-1 {
  300. algo = "sha1,rsa2048";
  301. value = <...conf 1 signature...>;
  302. };
  303. };
  304. };
  305. };
  306. You can see that we have added hashes for all images (since they are no
  307. longer signed), and a signature to each configuration. In the above example,
  308. mkimage will sign configurations/conf-1, the kernel and fdt that are
  309. pointed to by the configuration (/images/kernel-1, /images/kernel-1/hash-1,
  310. /images/fdt-1, /images/fdt-1/hash-1) and the root structure of the image
  311. (so that it isn't possible to add or remove root nodes). The signature is
  312. written into /configurations/conf-1/signature-1/value. It can easily be
  313. verified later even if the FIT has been signed with other keys in the
  314. meantime.
  315. Verification
  316. ------------
  317. FITs are verified when loaded. After the configuration is selected a list
  318. of required images is produced. If there are 'required' public keys, then
  319. each image must be verified against those keys. This means that every image
  320. that might be used by the target needs to be signed with 'required' keys.
  321. This happens automatically as part of a bootm command when FITs are used.
  322. For Signed Configurations, the default verification behavior can be changed by
  323. the following optional property in /signature node in U-Boot's control FDT.
  324. - required-mode: Valid values are "any" to allow verified boot to succeed if
  325. the selected configuration is signed by any of the 'required' keys, and "all"
  326. to allow verified boot to succeed if the selected configuration is signed by
  327. all of the 'required' keys.
  328. This property can be added to a binary device tree using fdtput as shown in
  329. below examples::
  330. fdtput -t s control.dtb /signature required-mode any
  331. fdtput -t s control.dtb /signature required-mode all
  332. Enabling FIT Verification
  333. -------------------------
  334. In addition to the options to enable FIT itself, the following CONFIGs must
  335. be enabled:
  336. CONFIG_FIT_SIGNATURE - enable signing and verification in FITs
  337. CONFIG_RSA - enable RSA algorithm for signing
  338. WARNING: When relying on signed FIT images with required signature check
  339. the legacy image format is default disabled by not defining
  340. CONFIG_LEGACY_IMAGE_FORMAT
  341. Testing
  342. -------
  343. An easy way to test signing and verification is to use the test script
  344. provided in test/vboot/vboot_test.sh. This uses sandbox (a special version
  345. of U-Boot which runs under Linux) to show the operation of a 'bootm'
  346. command loading and verifying images.
  347. A sample run is show below:
  348. $ make O=sandbox sandbox_config
  349. $ make O=sandbox
  350. $ O=sandbox ./test/vboot/vboot_test.sh
  351. Simple Verified Boot Test
  352. =========================
  353. Please see doc/uImage.FIT/verified-boot.txt for more information
  354. /home/hs/ids/u-boot/sandbox/tools/mkimage -D -I dts -O dtb -p 2000
  355. Build keys
  356. do sha1 test
  357. Build FIT with signed images
  358. Test Verified Boot Run: unsigned signatures:: OK
  359. Sign images
  360. Test Verified Boot Run: signed images: OK
  361. Build FIT with signed configuration
  362. Test Verified Boot Run: unsigned config: OK
  363. Sign images
  364. Test Verified Boot Run: signed config: OK
  365. check signed config on the host
  366. Signature check OK
  367. OK
  368. Test Verified Boot Run: signed config: OK
  369. Test Verified Boot Run: signed config with bad hash: OK
  370. do sha256 test
  371. Build FIT with signed images
  372. Test Verified Boot Run: unsigned signatures:: OK
  373. Sign images
  374. Test Verified Boot Run: signed images: OK
  375. Build FIT with signed configuration
  376. Test Verified Boot Run: unsigned config: OK
  377. Sign images
  378. Test Verified Boot Run: signed config: OK
  379. check signed config on the host
  380. Signature check OK
  381. OK
  382. Test Verified Boot Run: signed config: OK
  383. Test Verified Boot Run: signed config with bad hash: OK
  384. Test passed
  385. Software signing: keydir vs keyfile
  386. -----------------------------------
  387. In the simplest case, signing is done by giving mkimage the 'keyfile'. This is
  388. the path to a file containing the signing key.
  389. The alternative is to pass the 'keydir' argument. In this case the filename of
  390. the key is derived from the 'keydir' and the "key-name-hint" property in the
  391. FIT. In this case the "key-name-hint" property is mandatory, and the key must
  392. exist in "<keydir>/<key-name-hint>.<ext>" Here the extension "ext" is
  393. specific to the signing algorithm.
  394. Hardware Signing with PKCS#11 or with HSM
  395. -----------------------------------------
  396. Securely managing private signing keys can challenging, especially when the
  397. keys are stored on the file system of a computer that is connected to the
  398. Internet. If an attacker is able to steal the key, they can sign malicious FIT
  399. images which will appear genuine to your devices.
  400. An alternative solution is to keep your signing key securely stored on hardware
  401. device like a smartcard, USB token or Hardware Security Module (HSM) and have
  402. them perform the signing. PKCS#11 is standard for interfacing with these crypto
  403. device.
  404. Requirements:
  405. Smartcard/USB token/HSM which can work with some openssl engine
  406. openssl
  407. For pkcs11 engine usage:
  408. libp11 (provides pkcs11 engine)
  409. p11-kit (recommended to simplify setup)
  410. opensc (for smartcards and smartcard like USB devices)
  411. gnutls (recommended for key generation, p11tool)
  412. For generic HSMs respective openssl engine must be installed and locateable by
  413. openssl. This may require setting up LD_LIBRARY_PATH if engine is not installed
  414. to openssl's default search paths.
  415. PKCS11 engine support forms "key id" based on "keydir" and with
  416. "key-name-hint". "key-name-hint" is used as "object" name (if not defined in
  417. keydir). "keydir" (if defined) is used to define (prefix for) which PKCS11 source
  418. is being used for lookup up for the key.
  419. PKCS11 engine key ids:
  420. "pkcs11:<keydir>;object=<key-name-hint>;type=<public|private>"
  421. or, if keydir contains "object="
  422. "pkcs11:<keydir>;type=<public|private>"
  423. or
  424. "pkcs11:object=<key-name-hint>;type=<public|private>",
  425. Generic HSM engine support forms "key id" based on "keydir" and with
  426. "key-name-hint". If "keydir" is specified for mkimage it is used as a prefix in
  427. "key id" and is appended with "key-name-hint".
  428. Generic engine key ids:
  429. "<keydir><key-name-hint>"
  430. or
  431. "<key-name-hint>"
  432. In order to set the pin in the HSM, an environment variable "MKIMAGE_SIGN_PIN"
  433. can be specified.
  434. The following examples use the Nitrokey Pro using pkcs11 engine. Instructions
  435. for other devices may vary.
  436. Notes on pkcs11 engine setup:
  437. Make sure p11-kit, opensc are installed and that p11-kit is setup to use opensc.
  438. /usr/share/p11-kit/modules/opensc.module should be present on your system.
  439. Generating Keys On the Nitrokey:
  440. $ gpg --card-edit
  441. Reader ...........: Nitrokey Nitrokey Pro (xxxxxxxx0000000000000000) 00 00
  442. Application ID ...: xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
  443. Version ..........: 2.1
  444. Manufacturer .....: ZeitControl
  445. Serial number ....: xxxxxxxx
  446. Name of cardholder: [not set]
  447. Language prefs ...: de
  448. Sex ..............: unspecified
  449. URL of public key : [not set]
  450. Login data .......: [not set]
  451. Signature PIN ....: forced
  452. Key attributes ...: rsa2048 rsa2048 rsa2048
  453. Max. PIN lengths .: 32 32 32
  454. PIN retry counter : 3 0 3
  455. Signature counter : 0
  456. Signature key ....: [none]
  457. Encryption key....: [none]
  458. Authentication key: [none]
  459. General key info..: [none]
  460. gpg/card> generate
  461. Make off-card backup of encryption key? (Y/n) n
  462. Please note that the factory settings of the PINs are
  463. PIN = '123456' Admin PIN = '12345678'
  464. You should change them using the command --change-pin
  465. What keysize do you want for the Signature key? (2048) 4096
  466. The card will now be re-configured to generate a key of 4096 bits
  467. Note: There is no guarantee that the card supports the requested size.
  468. If the key generation does not succeed, please check the
  469. documentation of your card to see what sizes are allowed.
  470. What keysize do you want for the Encryption key? (2048) 4096
  471. The card will now be re-configured to generate a key of 4096 bits
  472. What keysize do you want for the Authentication key? (2048) 4096
  473. The card will now be re-configured to generate a key of 4096 bits
  474. Please specify how long the key should be valid.
  475. 0 = key does not expire
  476. <n> = key expires in n days
  477. <n>w = key expires in n weeks
  478. <n>m = key expires in n months
  479. <n>y = key expires in n years
  480. Key is valid for? (0)
  481. Key does not expire at all
  482. Is this correct? (y/N) y
  483. GnuPG needs to construct a user ID to identify your key.
  484. Real name: John Doe
  485. Email address: john.doe@email.com
  486. Comment:
  487. You selected this USER-ID:
  488. "John Doe <john.doe@email.com>"
  489. Change (N)ame, (C)omment, (E)mail or (O)kay/(Q)uit? o
  490. Using p11tool to get the token URL:
  491. Depending on system configuration, gpg-agent may need to be killed first.
  492. $ p11tool --provider /usr/lib/opensc-pkcs11.so --list-tokens
  493. Token 0:
  494. URL: pkcs11:model=PKCS%2315%20emulated;manufacturer=ZeitControl;serial=000xxxxxxxxx;token=OpenPGP%20card%20%28User%20PIN%20%28sig%29%29
  495. Label: OpenPGP card (User PIN (sig))
  496. Type: Hardware token
  497. Manufacturer: ZeitControl
  498. Model: PKCS#15 emulated
  499. Serial: 000xxxxxxxxx
  500. Module: (null)
  501. Token 1:
  502. URL: pkcs11:model=PKCS%2315%20emulated;manufacturer=ZeitControl;serial=000xxxxxxxxx;token=OpenPGP%20card%20%28User%20PIN%29
  503. Label: OpenPGP card (User PIN)
  504. Type: Hardware token
  505. Manufacturer: ZeitControl
  506. Model: PKCS#15 emulated
  507. Serial: 000xxxxxxxxx
  508. Module: (null)
  509. Use the portion of the signature token URL after "pkcs11:" as the keydir argument (-k) to mkimage below.
  510. Use the URL of the token to list the private keys:
  511. $ p11tool --login --provider /usr/lib/opensc-pkcs11.so --list-privkeys \
  512. "pkcs11:model=PKCS%2315%20emulated;manufacturer=ZeitControl;serial=000xxxxxxxxx;token=OpenPGP%20card%20%28User%20PIN%20%28sig%29%29"
  513. Token 'OpenPGP card (User PIN (sig))' with URL 'pkcs11:model=PKCS%2315%20emulated;manufacturer=ZeitControl;serial=000xxxxxxxxx;token=OpenPGP%20card%20%28User%20PIN%20%28sig%29%29' requires user PIN
  514. Enter PIN:
  515. Object 0:
  516. URL: pkcs11:model=PKCS%2315%20emulated;manufacturer=ZeitControl;serial=000xxxxxxxxx;token=OpenPGP%20card%20%28User%20PIN%20%28sig%29%29;id=%01;object=Signature%20key;type=private
  517. Type: Private key
  518. Label: Signature key
  519. Flags: CKA_PRIVATE; CKA_NEVER_EXTRACTABLE; CKA_SENSITIVE;
  520. ID: 01
  521. Use the label, in this case "Signature key" as the key-name-hint in your FIT.
  522. Create the fitImage:
  523. $ ./tools/mkimage -f fit-image.its fitImage
  524. Sign the fitImage with the hardware key:
  525. $ ./tools/mkimage -F -k \
  526. "model=PKCS%2315%20emulated;manufacturer=ZeitControl;serial=000xxxxxxxxx;token=OpenPGP%20card%20%28User%20PIN%20%28sig%29%29" \
  527. -K u-boot.dtb -N pkcs11 -r fitImage
  528. Future Work
  529. -----------
  530. - Roll-back protection using a TPM is done using the tpm command. This can
  531. be scripted, but we might consider a default way of doing this, built into
  532. bootm.
  533. Possible Future Work
  534. --------------------
  535. - Add support for other RSA/SHA variants, such as rsa4096,sha512.
  536. - Other algorithms besides RSA
  537. - More sandbox tests for failure modes
  538. - Passwords for keys/certificates
  539. - Perhaps implement OAEP
  540. - Enhance bootm to permit scripted signature verification (so that a script
  541. can verify an image but not actually boot it)
  542. Simon Glass
  543. sjg@chromium.org
  544. 1-1-13