also.
-Creating an RSA key and certificate
------------------------------------
-To create a new public key, size 2048 bits:
+Creating an RSA key pair and certificate
+----------------------------------------
+To create a new public/private key pair, size 2048 bits:
$ openssl genpkey -algorithm RSA -out keys/dev.key \
-pkeyopt rsa_keygen_bits:2048 -pkeyopt rsa_keygen_pubexp:65537
-To create a certificate for this:
+To create a certificate for this containing the public key:
$ openssl req -batch -new -x509 -key keys/dev.key -out keys/dev.crt
Device Tree Bindings
--------------------
The following properties are required in the FIT's signature node(s) to
-allow thes signer to operate. These should be added to the .its file.
+allow the signer to operate. These should be added to the .its file.
Signature nodes sit at the same level as hash nodes and are called
-signature@1, signature@2, etc.
+signature-1, signature-2, etc.
-- algo: Algorithm name (e.g. "sha1,rs2048")
+- algo: Algorithm name (e.g. "sha1,rsa2048")
- key-name-hint: Name of key to use for signing. The keys will normally be in
a single directory (parameter -k to mkimage). For a given key <name>, its
- comment: Additional information about the signer or image
+- padding: The padding algorithm, it may be pkcs-1.5 or pss,
+ if no value is provided we assume pkcs-1.5
+
For config bindings (see Signed Configurations below), the following
additional properties are optional:
- hashed-nodes: A list of nodes which were hashed by the signer. Each is
a string - the full path to node. A typical value might be:
- hashed-nodes = "/", "/configurations/conf@1", "/images/kernel@1",
- "/images/kernel@1/hash@1", "/images/fdt@1",
- "/images/fdt@1/hash@1";
+ hashed-nodes = "/", "/configurations/conf-1", "/images/kernel",
+ "/images/kernel/hash-1", "/images/fdt-1",
+ "/images/fdt-1/hash-1";
- hashed-strings: The start and size of the string region of the FIT that
was hashed
Public keys should be stored as sub-nodes in a /signature node. Required
properties are:
-- algo: Algorithm name (e.g. "sha1,rs2048")
+- algo: Algorithm name (e.g. "sha1,rsa2048" or "sha256,ecdsa256")
Optional properties are:
- required: If present this indicates that the key must be verified for the
image / configuration to be considered valid. Only required keys are
normally verified by the FIT image booting algorithm. Valid values are
-"image" to force verification of all images, and "conf" to force verfication
+"image" to force verification of all images, and "conf" to force verification
of the selected configuration (which then relies on hashes in the images to
verify those).
- rsa,r-squared: (2^num-bits)^2 as a big-endian multi-word integer
- rsa,n0-inverse: -1 / modulus[0] mod 2^32
+For ECDSA the following are mandatory:
+- ecdsa,curve: Name of ECDSA curve (e.g. "prime256v1")
+- ecdsa,x-point: Public key X coordinate as a big-endian multi-word integer
+- ecdsa,y-point: Public key Y coordinate as a big-endian multi-word integer
+
+These parameters can be added to a binary device tree using parameter -K of the
+mkimage command::
+
+ tools/mkimage -f fit.its -K control.dtb -k keys -r image.fit
+
+Here is an example of a generated device tree node::
+
+ signature {
+ key-dev {
+ required = "conf";
+ algo = "sha256,rsa2048";
+ rsa,r-squared = <0xb76d1acf 0xa1763ca5 0xeb2f126
+ 0x742edc80 0xd3f42177 0x9741d9d9
+ 0x35bb476e 0xff41c718 0xd3801430
+ 0xf22537cb 0xa7e79960 0xae32a043
+ 0x7da1427a 0x341d6492 0x3c2762f5
+ 0xaac04726 0x5b262d96 0xf984e86d
+ 0xb99443c7 0x17080c33 0x940f6892
+ 0xd57a95d1 0x6ea7b691 0xc5038fa8
+ 0x6bb48a6e 0x73f1b1ea 0x37160841
+ 0xe05715ce 0xa7c45bbd 0x690d82d5
+ 0x99c2454c 0x6ff117b3 0xd830683b
+ 0x3f81c9cf 0x1ca38a91 0x0c3392e4
+ 0xd817c625 0x7b8e9a24 0x175b89ea
+ 0xad79f3dc 0x4d50d7b4 0x9d4e90f8
+ 0xad9e2939 0xc165d6a4 0x0ada7e1b
+ 0xfb1bf495 0xfc3131c2 0xb8c6e604
+ 0xc2761124 0xf63de4a6 0x0e9565f9
+ 0xc8e53761 0x7e7a37a5 0xe99dcdae
+ 0x9aff7e1e 0xbd44b13d 0x6b0e6aa4
+ 0x038907e4 0x8e0d6850 0xef51bc20
+ 0xf73c94af 0x88bea7b1 0xcbbb1b30
+ 0xd024b7f3>;
+ rsa,modulus = <0xc0711d6cb 0x9e86db7f 0x45986dbe
+ 0x023f1e8c9 0xe1a4c4d0 0x8a0dfdc9
+ 0x023ba0c48 0x06815f6a 0x5caa0654
+ 0x07078c4b7 0x3d154853 0x40729023
+ 0x0b007c8fe 0x5a3647e5 0x23b41e20
+ 0x024720591 0x66915305 0x0e0b29b0
+ 0x0de2ad30d 0x8589430f 0xb1590325
+ 0x0fb9f5d5e 0x9eba752a 0xd88e6de9
+ 0x056b3dcc6 0x9a6b8e61 0x6784f61f
+ 0x000f39c21 0x5eec6b33 0xd78e4f78
+ 0x0921a305f 0xaa2cc27e 0x1ca917af
+ 0x06e1134f4 0xd48cac77 0x4e914d07
+ 0x0f707aa5a 0x0d141f41 0x84677f1d
+ 0x0ad47a049 0x028aedb6 0xd5536fcf
+ 0x03fef1e4f 0x133a03d2 0xfd7a750a
+ 0x0f9159732 0xd207812e 0x6a807375
+ 0x06434230d 0xc8e22dad 0x9f29b3d6
+ 0x07c44ac2b 0xfa2aad88 0xe2429504
+ 0x041febd41 0x85d0d142 0x7b194d65
+ 0x06e5d55ea 0x41116961 0xf3181dde
+ 0x068bf5fbc 0x3dd82047 0x00ee647e
+ 0x0d7a44ab3>;
+ rsa,exponent = <0x00 0x10001>;
+ rsa,n0-inverse = <0xb3928b85>;
+ rsa,num-bits = <0x800>;
+ key-name-hint = "dev";
+ };
+ };
+
Signed Configurations
---------------------
/ {
images {
- kernel@1 {
+ kernel-1 {
data = <data for kernel1>
- signature@1 {
+ signature-1 {
algo = "sha1,rsa2048";
value = <...kernel signature 1...>
};
};
- kernel@2 {
+ kernel-2 {
data = <data for kernel2>
- signature@1 {
+ signature-1 {
algo = "sha1,rsa2048";
value = <...kernel signature 2...>
};
};
- fdt@1 {
+ fdt-1 {
data = <data for fdt1>;
- signature@1 {
+ signature-1 {
algo = "sha1,rsa2048";
- vaue = <...fdt signature 1...>
+ value = <...fdt signature 1...>
};
};
- fdt@2 {
+ fdt-2 {
data = <data for fdt2>;
- signature@1 {
+ signature-1 {
algo = "sha1,rsa2048";
- vaue = <...fdt signature 2...>
+ value = <...fdt signature 2...>
};
};
};
configurations {
- default = "conf@1";
- conf@1 {
- kernel = "kernel@1";
- fdt = "fdt@1";
+ default = "conf-1";
+ conf-1 {
+ kernel = "kernel-1";
+ fdt = "fdt-1";
};
- conf@1 {
- kernel = "kernel@2";
- fdt = "fdt@2";
+ conf-2 {
+ kernel = "kernel-2";
+ fdt = "fdt-2";
};
};
};
configuration 3 with kernel 1 and fdt 2:
configurations {
- default = "conf@1";
- conf@1 {
- kernel = "kernel@1";
- fdt = "fdt@1";
+ default = "conf-1";
+ conf-1 {
+ kernel = "kernel-1";
+ fdt = "fdt-1";
};
- conf@1 {
- kernel = "kernel@2";
- fdt = "fdt@2";
+ conf-2 {
+ kernel = "kernel-2";
+ fdt = "fdt-2";
};
- conf@3 {
- kernel = "kernel@1";
- fdt = "fdt@2";
+ conf-3 {
+ kernel = "kernel-1";
+ fdt = "fdt-2";
};
};
With signed images, nothing protects against this. Whether it gains an
advantage for the attacker is debatable, but it is not secure.
-To solved this problem, we support signed configurations. In this case it
+To solve this problem, we support signed configurations. In this case it
is the configurations that are signed, not the image. Each image has its
own hash, and we include the hash in the configuration signature.
/ {
images {
- kernel@1 {
+ kernel-1 {
data = <data for kernel1>
- hash@1 {
+ hash-1 {
algo = "sha1";
value = <...kernel hash 1...>
};
};
- kernel@2 {
+ kernel-2 {
data = <data for kernel2>
- hash@1 {
+ hash-1 {
algo = "sha1";
value = <...kernel hash 2...>
};
};
- fdt@1 {
+ fdt-1 {
data = <data for fdt1>;
- hash@1 {
+ hash-1 {
algo = "sha1";
value = <...fdt hash 1...>
};
};
- fdt@2 {
+ fdt-2 {
data = <data for fdt2>;
- hash@1 {
+ hash-1 {
algo = "sha1";
value = <...fdt hash 2...>
};
};
};
configurations {
- default = "conf@1";
- conf@1 {
- kernel = "kernel@1";
- fdt = "fdt@1";
- signature@1 {
+ default = "conf-1";
+ conf-1 {
+ kernel = "kernel-1";
+ fdt = "fdt-1";
+ signature-1 {
algo = "sha1,rsa2048";
value = <...conf 1 signature...>;
};
};
- conf@2 {
- kernel = "kernel@2";
- fdt = "fdt@2";
- signature@1 {
+ conf-2 {
+ kernel = "kernel-2";
+ fdt = "fdt-2";
+ signature-1 {
algo = "sha1,rsa2048";
value = <...conf 1 signature...>;
};
You can see that we have added hashes for all images (since they are no
longer signed), and a signature to each configuration. In the above example,
-mkimage will sign configurations/conf@1, the kernel and fdt that are
-pointed to by the configuration (/images/kernel@1, /images/kernel@1/hash@1,
-/images/fdt@1, /images/fdt@1/hash@1) and the root structure of the image
+mkimage will sign configurations/conf-1, the kernel and fdt that are
+pointed to by the configuration (/images/kernel-1, /images/kernel-1/hash-1,
+/images/fdt-1, /images/fdt-1/hash-1) and the root structure of the image
(so that it isn't possible to add or remove root nodes). The signature is
-written into /configurations/conf@1/signature@1/value. It can easily be
+written into /configurations/conf-1/signature-1/value. It can easily be
verified later even if the FIT has been signed with other keys in the
meantime.
This happens automatically as part of a bootm command when FITs are used.
+For Signed Configurations, the default verification behavior can be changed by
+the following optional property in /signature node in U-Boot's control FDT.
+
+- required-mode: Valid values are "any" to allow verified boot to succeed if
+the selected configuration is signed by any of the 'required' keys, and "all"
+to allow verified boot to succeed if the selected configuration is signed by
+all of the 'required' keys.
+
+This property can be added to a binary device tree using fdtput as shown in
+below examples::
+
+ fdtput -t s control.dtb /signature required-mode any
+ fdtput -t s control.dtb /signature required-mode all
+
Enabling FIT Verification
-------------------------
In addition to the options to enable FIT itself, the following CONFIGs must
be enabled:
-CONFIG_FIT_SIGNATURE - enable signing and verfication in FITs
+CONFIG_FIT_SIGNATURE - enable signing and verification in FITs
CONFIG_RSA - enable RSA algorithm for signing
WARNING: When relying on signed FIT images with required signature check
the legacy image format is default disabled by not defining
-CONFIG_IMAGE_FORMAT_LEGACY
+CONFIG_LEGACY_IMAGE_FORMAT
+
Testing
-------
-An easy way to test signing and verfication is to use the test script
+An easy way to test signing and verification is to use the test script
provided in test/vboot/vboot_test.sh. This uses sandbox (a special version
of U-Boot which runs under Linux) to show the operation of a 'bootm'
command loading and verifying images.
$ make O=sandbox sandbox_config
$ make O=sandbox
$ O=sandbox ./test/vboot/vboot_test.sh
+
+
Simple Verified Boot Test
=========================
Test passed
+Software signing: keydir vs keyfile
+-----------------------------------
+
+In the simplest case, signing is done by giving mkimage the 'keyfile'. This is
+the path to a file containing the signing key.
+
+The alternative is to pass the 'keydir' argument. In this case the filename of
+the key is derived from the 'keydir' and the "key-name-hint" property in the
+FIT. In this case the "key-name-hint" property is mandatory, and the key must
+exist in "<keydir>/<key-name-hint>.<ext>" Here the extension "ext" is
+specific to the signing algorithm.
+
+
+Hardware Signing with PKCS#11 or with HSM
+-----------------------------------------
+
+Securely managing private signing keys can challenging, especially when the
+keys are stored on the file system of a computer that is connected to the
+Internet. If an attacker is able to steal the key, they can sign malicious FIT
+images which will appear genuine to your devices.
+
+An alternative solution is to keep your signing key securely stored on hardware
+device like a smartcard, USB token or Hardware Security Module (HSM) and have
+them perform the signing. PKCS#11 is standard for interfacing with these crypto
+device.
+
+Requirements:
+Smartcard/USB token/HSM which can work with some openssl engine
+openssl
+
+For pkcs11 engine usage:
+libp11 (provides pkcs11 engine)
+p11-kit (recommended to simplify setup)
+opensc (for smartcards and smartcard like USB devices)
+gnutls (recommended for key generation, p11tool)
+
+For generic HSMs respective openssl engine must be installed and locateable by
+openssl. This may require setting up LD_LIBRARY_PATH if engine is not installed
+to openssl's default search paths.
+
+PKCS11 engine support forms "key id" based on "keydir" and with
+"key-name-hint". "key-name-hint" is used as "object" name (if not defined in
+keydir). "keydir" (if defined) is used to define (prefix for) which PKCS11 source
+is being used for lookup up for the key.
+
+PKCS11 engine key ids:
+ "pkcs11:<keydir>;object=<key-name-hint>;type=<public|private>"
+or, if keydir contains "object="
+ "pkcs11:<keydir>;type=<public|private>"
+or
+ "pkcs11:object=<key-name-hint>;type=<public|private>",
+
+Generic HSM engine support forms "key id" based on "keydir" and with
+"key-name-hint". If "keydir" is specified for mkimage it is used as a prefix in
+"key id" and is appended with "key-name-hint".
+
+Generic engine key ids:
+ "<keydir><key-name-hint>"
+or
+ "<key-name-hint>"
+
+In order to set the pin in the HSM, an environment variable "MKIMAGE_SIGN_PIN"
+can be specified.
+
+The following examples use the Nitrokey Pro using pkcs11 engine. Instructions
+for other devices may vary.
+
+Notes on pkcs11 engine setup:
+
+Make sure p11-kit, opensc are installed and that p11-kit is setup to use opensc.
+/usr/share/p11-kit/modules/opensc.module should be present on your system.
+
+
+Generating Keys On the Nitrokey:
+
+$ gpg --card-edit
+
+Reader ...........: Nitrokey Nitrokey Pro (xxxxxxxx0000000000000000) 00 00
+Application ID ...: xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
+Version ..........: 2.1
+Manufacturer .....: ZeitControl
+Serial number ....: xxxxxxxx
+Name of cardholder: [not set]
+Language prefs ...: de
+Sex ..............: unspecified
+URL of public key : [not set]
+Login data .......: [not set]
+Signature PIN ....: forced
+Key attributes ...: rsa2048 rsa2048 rsa2048
+Max. PIN lengths .: 32 32 32
+PIN retry counter : 3 0 3
+Signature counter : 0
+Signature key ....: [none]
+Encryption key....: [none]
+Authentication key: [none]
+General key info..: [none]
+
+gpg/card> generate
+Make off-card backup of encryption key? (Y/n) n
+
+Please note that the factory settings of the PINs are
+ PIN = '123456' Admin PIN = '12345678'
+You should change them using the command --change-pin
+
+What keysize do you want for the Signature key? (2048) 4096
+The card will now be re-configured to generate a key of 4096 bits
+Note: There is no guarantee that the card supports the requested size.
+ If the key generation does not succeed, please check the
+ documentation of your card to see what sizes are allowed.
+What keysize do you want for the Encryption key? (2048) 4096
+The card will now be re-configured to generate a key of 4096 bits
+What keysize do you want for the Authentication key? (2048) 4096
+The card will now be re-configured to generate a key of 4096 bits
+Please specify how long the key should be valid.
+ 0 = key does not expire
+ <n> = key expires in n days
+ <n>w = key expires in n weeks
+ <n>m = key expires in n months
+ <n>y = key expires in n years
+Key is valid for? (0)
+Key does not expire at all
+Is this correct? (y/N) y
+
+GnuPG needs to construct a user ID to identify your key.
+
+Real name: John Doe
+Email address: john.doe@email.com
+Comment:
+You selected this USER-ID:
+ "John Doe <john.doe@email.com>"
+
+Change (N)ame, (C)omment, (E)mail or (O)kay/(Q)uit? o
+
+
+Using p11tool to get the token URL:
+
+Depending on system configuration, gpg-agent may need to be killed first.
+
+$ p11tool --provider /usr/lib/opensc-pkcs11.so --list-tokens
+Token 0:
+URL: pkcs11:model=PKCS%2315%20emulated;manufacturer=ZeitControl;serial=000xxxxxxxxx;token=OpenPGP%20card%20%28User%20PIN%20%28sig%29%29
+Label: OpenPGP card (User PIN (sig))
+Type: Hardware token
+Manufacturer: ZeitControl
+Model: PKCS#15 emulated
+Serial: 000xxxxxxxxx
+Module: (null)
+
+
+Token 1:
+URL: pkcs11:model=PKCS%2315%20emulated;manufacturer=ZeitControl;serial=000xxxxxxxxx;token=OpenPGP%20card%20%28User%20PIN%29
+Label: OpenPGP card (User PIN)
+Type: Hardware token
+Manufacturer: ZeitControl
+Model: PKCS#15 emulated
+Serial: 000xxxxxxxxx
+Module: (null)
+
+Use the portion of the signature token URL after "pkcs11:" as the keydir argument (-k) to mkimage below.
+
+
+Use the URL of the token to list the private keys:
+
+$ p11tool --login --provider /usr/lib/opensc-pkcs11.so --list-privkeys \
+"pkcs11:model=PKCS%2315%20emulated;manufacturer=ZeitControl;serial=000xxxxxxxxx;token=OpenPGP%20card%20%28User%20PIN%20%28sig%29%29"
+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
+Enter PIN:
+Object 0:
+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
+Type: Private key
+Label: Signature key
+Flags: CKA_PRIVATE; CKA_NEVER_EXTRACTABLE; CKA_SENSITIVE;
+ID: 01
+
+Use the label, in this case "Signature key" as the key-name-hint in your FIT.
+
+Create the fitImage:
+$ ./tools/mkimage -f fit-image.its fitImage
+
+
+Sign the fitImage with the hardware key:
+
+$ ./tools/mkimage -F -k \
+"model=PKCS%2315%20emulated;manufacturer=ZeitControl;serial=000xxxxxxxxx;token=OpenPGP%20card%20%28User%20PIN%20%28sig%29%29" \
+-K u-boot.dtb -N pkcs11 -r fitImage
+
+
Future Work
-----------
- Roll-back protection using a TPM is done using the tpm command. This can
projects / platform / kernel / u-boot.git / blobdiff