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")
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).
/ {
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...>
};
};
- fdt@2 {
+ fdt-2 {
data = <data for fdt2>;
- signature@1 {
+ signature-1 {
algo = "sha1,rsa2048";
vaue = <...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-1 {
+ 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-1 {
+ 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.
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
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.
Test passed
+Hardware Signing with PKCS#11
+-----------------------------
+
+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 the pkcs11 engine
+openssl
+libp11 (provides pkcs11 engine)
+p11-kit (recommended to simplify setup)
+opensc (for smartcards and smartcard like USB devices)
+gnutls (recommended for key generation, p11tool)
+
+The following examples use the Nitrokey Pro. 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