[J-u-boot.git] / doc / uImage.FIT / signature.txt

U-Boot FIT Signature Verification
=================================

Introduction
------------
FIT supports hashing of images so that these hashes can be checked on
loading. This protects against corruption of the image. However it does not
prevent the substitution of one image for another.

The signature feature allows the hash to be signed with a private key such
that it can be verified using a public key later. Provided that the private
key is kept secret and the public key is stored in a non-volatile place,
any image can be verified in this way.

See verified-boot.txt for more general information on verified boot.


Concepts
--------
Some familiarity with public key cryptography is assumed in this section.

The procedure for signing is as follows:

   - hash an image in the FIT
   - sign the hash with a private key to produce a signature
   - store the resulting signature in the FIT

The procedure for verification is:

   - read the FIT
   - obtain the public key
   - extract the signature from the FIT
   - hash the image from the FIT
   - verify (with the public key) that the extracted signature matches the
       hash

The signing is generally performed by mkimage, as part of making a firmware
image for the device. The verification is normally done in U-Boot on the
device.


Algorithms
----------
In principle any suitable algorithm can be used to sign and verify a hash.
At present only one class of algorithms is supported: SHA1 hashing with RSA.
This works by hashing the image to produce a 20-byte hash.

While it is acceptable to bring in large cryptographic libraries such as
openssl on the host side (e.g. mkimage), it is not desirable for U-Boot.
For the run-time verification side, it is important to keep code and data
size as small as possible.

For this reason the RSA image verification uses pre-processed public keys
which can be used with a very small amount of code - just some extraction
of data from the FDT and exponentiation mod n. Code size impact is a little
under 5KB on Tegra Seaboard, for example.

It is relatively straightforward to add new algorithms if required. If
another RSA variant is needed, then it can be added to the table in
image-sig.c. If another algorithm is needed (such as DSA) then it can be
placed alongside rsa.c, and its functions added to the table in image-sig.c
also.


Creating an RSA key and certificate
-----------------------------------
To create a new public key, size 2048 bits:

$ openssl genrsa -F4 -out keys/dev.key 2048

To create a certificate for this:

$ openssl req -batch -new -x509 -key keys/dev.key -out keys/dev.crt

If you like you can look at the public key also:

$ openssl rsa -in keys/dev.key -pubout


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.
Signature nodes sit at the same level as hash nodes and are called
signature@1, signature@2, etc.

- algo: Algorithm name (e.g. "sha1,rs2048")

- 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
private key is stored in <name>.key and the certificate is stored in
<name>.crt.

When the image is signed, the following properties are added (mandatory):

- value: The signature data (e.g. 256 bytes for 2048-bit RSA)

When the image is signed, the following properties are optional:

- timestamp: Time when image was signed (standard Unix time_t format)

- signer-name: Name of the signer (e.g. "mkimage")

- signer-version: Version string of the signer (e.g. "2013.01")

- comment: Additional information about the signer or image

For config bindings (see Signed Configurations below), the following
additional properties are optional:

- sign-images: A list of images to sign, each being a property of the conf
node that contains then. The default is "kernel,fdt" which means that these
two images will be looked up in the config and signed if present.

For config bindings, these properties are added by the signer:

- 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-strings: The start and size of the string region of the FIT that
	was hashed

Example: See sign-images.its for an example image tree source file and
sign-configs.its for config signing.


Public Key Storage
------------------
In order to verify an image that has been signed with a public key we need to
have a trusted public key. This cannot be stored in the signed image, since
it would be easy to alter. For this implementation we choose to store the
public key in U-Boot's control FDT (using CONFIG_OF_CONTROL).

Public keys should be stored as sub-nodes in a /signature node. Required
properties are:

- algo: Algorithm name (e.g. "sha1,rs2048")

Optional properties are:

- key-name-hint: Name of key used for signing. This is only a hint since it
is possible for the name to be changed. Verification can proceed by checking
all available signing keys until one matches.

- 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
of the selected configuration (which then relies on hashes in the images to
verify those).

Each signing algorithm has its own additional properties.

For RSA the following are mandatory:

- rsa,num-bits: Number of key bits (e.g. 2048)
- rsa,modulus: Modulus (N) as a big-endian multi-word integer
- rsa,r-squared: (2^num-bits)^2 as a big-endian multi-word integer
- rsa,n0-inverse: -1 / modulus[0] mod 2^32


Signed Configurations
---------------------
While signing images is useful, it does not provide complete protection
against several types of attack. For example, it it possible to create a
FIT with the same signed images, but with the configuration changed such
that a different one is selected (mix and match attack). It is also possible
to substitute a signed image from an older FIT version into a newer FIT
(roll-back attack).

As an example, consider this FIT:

/ {
	images {
		kernel@1 {
			data = <data for kernel1>
			signature@1 {
				algo = "sha1,rsa2048";
				value = <...kernel signature 1...>
			};
		};
		kernel@2 {
			data = <data for kernel2>
			signature@1 {
				algo = "sha1,rsa2048";
				value = <...kernel signature 2...>
			};
		};
		fdt@1 {
			data = <data for fdt1>;
			signature@1 {
				algo = "sha1,rsa2048";
				vaue = <...fdt signature 1...>
			};
		};
		fdt@2 {
			data = <data for fdt2>;
			signature@1 {
				algo = "sha1,rsa2048";
				vaue = <...fdt signature 2...>
			};
		};
	};
	configurations {
		default = "conf@1";
		conf@1 {
			kernel = "kernel@1";
			fdt = "fdt@1";
		};
		conf@1 {
			kernel = "kernel@2";
			fdt = "fdt@2";
		};
	};
};

Since both kernels are signed it is easy for an attacker to add a new
configuration 3 with kernel 1 and fdt 2:

	configurations {
		default = "conf@1";
		conf@1 {
			kernel = "kernel@1";
			fdt = "fdt@1";
		};
		conf@1 {
			kernel = "kernel@2";
			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
is the configurations that are signed, not the image. Each image has its
own hash, and we include the hash in the configuration signature.

So the above example is adjusted to look like this:

/ {
	images {
		kernel@1 {
			data = <data for kernel1>
			hash@1 {
				algo = "sha1";
				value = <...kernel hash 1...>
			};
		};
		kernel@2 {
			data = <data for kernel2>
			hash@1 {
				algo = "sha1";
				value = <...kernel hash 2...>
			};
		};
		fdt@1 {
			data = <data for fdt1>;
			hash@1 {
				algo = "sha1";
				value = <...fdt hash 1...>
			};
		};
		fdt@2 {
			data = <data for fdt2>;
			hash@1 {
				algo = "sha1";
				value = <...fdt hash 2...>
			};
		};
	};
	configurations {
		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 {
				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
(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
verified later even if the FIT has been signed with other keys in the
meantime.


Verification
------------
FITs are verified when loaded. After the configuration is selected a list
of required images is produced. If there are 'required' public keys, then
each image must be verified against those keys. This means that every image
that might be used by the target needs to be signed with 'required' keys.

This happens automatically as part of a bootm command when FITs are used.


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_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

Testing
-------
An easy way to test signing and verfication 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.

A sample run is show below:

$ make O=sandbox sandbox_config
$ make O=sandbox
$ O=sandbox ./test/vboot/vboot_test.sh
Simple Verified Boot Test
=========================

Please see doc/uImage.FIT/verified-boot.txt for more information

/home/hs/ids/u-boot/sandbox/tools/mkimage -D -I dts -O dtb -p 2000
Build keys
do sha1 test
Build FIT with signed images
Test Verified Boot Run: unsigned signatures:: OK
Sign images
Test Verified Boot Run: signed images: OK
Build FIT with signed configuration
Test Verified Boot Run: unsigned config: OK
Sign images
Test Verified Boot Run: signed config: OK
check signed config on the host
Signature check OK
OK
Test Verified Boot Run: signed config: OK
Test Verified Boot Run: signed config with bad hash: OK
do sha256 test
Build FIT with signed images
Test Verified Boot Run: unsigned signatures:: OK
Sign images
Test Verified Boot Run: signed images: OK
Build FIT with signed configuration
Test Verified Boot Run: unsigned config: OK
Sign images
Test Verified Boot Run: signed config: OK
check signed config on the host
Signature check OK
OK
Test Verified Boot Run: signed config: OK
Test Verified Boot Run: signed config with bad hash: OK

Test passed


Future Work
-----------
- Roll-back protection using a TPM is done using the tpm command. This can
be scripted, but we might consider a default way of doing this, built into
bootm.


Possible Future Work
--------------------
- Add support for other RSA/SHA variants, such as rsa4096,sha512.
- Other algorithms besides RSA
- More sandbox tests for failure modes
- Passwords for keys/certificates
- Perhaps implement OAEP
- Enhance bootm to permit scripted signature verification (so that a script
can verify an image but not actually boot it)


Simon Glass
[email protected]
1-1-13
Commit	Line	Data
3e569a6b SG	1	U-Boot FIT Signature Verification
	2	=================================
	3
	4	Introduction
	5	------------
	6	FIT supports hashing of images so that these hashes can be checked on
	7	loading. This protects against corruption of the image. However it does not
	8	prevent the substitution of one image for another.
	9
	10	The signature feature allows the hash to be signed with a private key such
	11	that it can be verified using a public key later. Provided that the private
	12	key is kept secret and the public key is stored in a non-volatile place,
	13	any image can be verified in this way.
	14
	15	See verified-boot.txt for more general information on verified boot.
	16
	17
	18	Concepts
	19	--------
	20	Some familiarity with public key cryptography is assumed in this section.
	21
	22	The procedure for signing is as follows:
	23
	24	- hash an image in the FIT
	25	- sign the hash with a private key to produce a signature
	26	- store the resulting signature in the FIT
	27
	28	The procedure for verification is:
	29
	30	- read the FIT
	31	- obtain the public key
	32	- extract the signature from the FIT
	33	- hash the image from the FIT
	34	- verify (with the public key) that the extracted signature matches the
	35	hash
	36
	37	The signing is generally performed by mkimage, as part of making a firmware
	38	image for the device. The verification is normally done in U-Boot on the
	39	device.
	40
	41
	42	Algorithms
	43	----------
	44	In principle any suitable algorithm can be used to sign and verify a hash.
	45	At present only one class of algorithms is supported: SHA1 hashing with RSA.
	46	This works by hashing the image to produce a 20-byte hash.
	47
	48	While it is acceptable to bring in large cryptographic libraries such as
	49	openssl on the host side (e.g. mkimage), it is not desirable for U-Boot.
	50	For the run-time verification side, it is important to keep code and data
	51	size as small as possible.
	52
	53	For this reason the RSA image verification uses pre-processed public keys
	54	which can be used with a very small amount of code - just some extraction
	55	of data from the FDT and exponentiation mod n. Code size impact is a little
	56	under 5KB on Tegra Seaboard, for example.
	57
	58	It is relatively straightforward to add new algorithms if required. If
	59	another RSA variant is needed, then it can be added to the table in
	60	image-sig.c. If another algorithm is needed (such as DSA) then it can be
	61	placed alongside rsa.c, and its functions added to the table in image-sig.c
	62	also.
	63
	64
65	Creating an RSA key and certificate
66	-----------------------------------
67	To create a new public key, size 2048 bits:
68
69	$ openssl genrsa -F4 -out keys/dev.key 2048
70
71	To create a certificate for this:
72
73	$ openssl req -batch -new -x509 -key keys/dev.key -out keys/dev.crt
74
75	If you like you can look at the public key also:
76
77	$ openssl rsa -in keys/dev.key -pubout
78
79
80	Device Tree Bindings
81	--------------------
82	The following properties are required in the FIT's signature node(s) to
83	allow thes signer to operate. These should be added to the .its file.
84	Signature nodes sit at the same level as hash nodes and are called
85	signature@1, signature@2, etc.
86
87	- algo: Algorithm name (e.g. "sha1,rs2048")
88
89	- key-name-hint: Name of key to use for signing. The keys will normally be in
90	a single directory (parameter -k to mkimage). For a given key <name>, its
91	private key is stored in <name>.key and the certificate is stored in
92	<name>.crt.
93
94	When the image is signed, the following properties are added (mandatory):
95
96	- value: The signature data (e.g. 256 bytes for 2048-bit RSA)
97
98	When the image is signed, the following properties are optional:
99
100	- timestamp: Time when image was signed (standard Unix time_t format)
101
102	- signer-name: Name of the signer (e.g. "mkimage")
103
104	- signer-version: Version string of the signer (e.g. "2013.01")
105
106	- comment: Additional information about the signer or image
107
4d098529 SG	108	For config bindings (see Signed Configurations below), the following
4d098529 SG	109	additional properties are optional:
3e569a6b	110
4d098529 SG	111	- sign-images: A list of images to sign, each being a property of the conf
	112	node that contains then. The default is "kernel,fdt" which means that these
	113	two images will be looked up in the config and signed if present.
	114
	115	For config bindings, these properties are added by the signer:
	116
	117	- hashed-nodes: A list of nodes which were hashed by the signer. Each is
	118	a string - the full path to node. A typical value might be:
	119
	120	hashed-nodes = "/", "/configurations/conf@1", "/images/kernel@1",
	121	"/images/kernel@1/hash@1", "/images/fdt@1",
	122	"/images/fdt@1/hash@1";
	123
	124	- hashed-strings: The start and size of the string region of the FIT that
	125	was hashed
	126
	127	Example: See sign-images.its for an example image tree source file and
	128	sign-configs.its for config signing.
3e569a6b SG	129
	130
	131	Public Key Storage
	132	------------------
	133	In order to verify an image that has been signed with a public key we need to
	134	have a trusted public key. This cannot be stored in the signed image, since
	135	it would be easy to alter. For this implementation we choose to store the
	136	public key in U-Boot's control FDT (using CONFIG_OF_CONTROL).
	137
	138	Public keys should be stored as sub-nodes in a /signature node. Required
	139	properties are:
	140
	141	- algo: Algorithm name (e.g. "sha1,rs2048")
	142
	143	Optional properties are:
	144
	145	- key-name-hint: Name of key used for signing. This is only a hint since it
	146	is possible for the name to be changed. Verification can proceed by checking
	147	all available signing keys until one matches.
	148
	149	- required: If present this indicates that the key must be verified for the
	150	image / configuration to be considered valid. Only required keys are
	151	normally verified by the FIT image booting algorithm. Valid values are
	152	"image" to force verification of all images, and "conf" to force verfication
	153	of the selected configuration (which then relies on hashes in the images to
	154	verify those).
	155
	156	Each signing algorithm has its own additional properties.
	157
	158	For RSA the following are mandatory:
	159
	160	- rsa,num-bits: Number of key bits (e.g. 2048)
	161	- rsa,modulus: Modulus (N) as a big-endian multi-word integer
	162	- rsa,r-squared: (2^num-bits)^2 as a big-endian multi-word integer
	163	- rsa,n0-inverse: -1 / modulus[0] mod 2^32
	164
	165
4d098529 SG	166	Signed Configurations
	167	---------------------
	168	While signing images is useful, it does not provide complete protection
	169	against several types of attack. For example, it it possible to create a
	170	FIT with the same signed images, but with the configuration changed such
	171	that a different one is selected (mix and match attack). It is also possible
	172	to substitute a signed image from an older FIT version into a newer FIT
	173	(roll-back attack).
	174
	175	As an example, consider this FIT:
	176
	177	/ {
	178	images {
	179	kernel@1 {
	180	data = <data for kernel1>
	181	signature@1 {
	182	algo = "sha1,rsa2048";
	183	value = <...kernel signature 1...>
	184	};
	185	};
	186	kernel@2 {
	187	data = <data for kernel2>
	188	signature@1 {
	189	algo = "sha1,rsa2048";
	190	value = <...kernel signature 2...>
	191	};
	192	};
	193	fdt@1 {
	194	data = <data for fdt1>;
	195	signature@1 {
	196	algo = "sha1,rsa2048";
	197	vaue = <...fdt signature 1...>
	198	};
	199	};
	200	fdt@2 {
	201	data = <data for fdt2>;
	202	signature@1 {
	203	algo = "sha1,rsa2048";
	204	vaue = <...fdt signature 2...>
	205	};
	206	};
	207	};
	208	configurations {
	209	default = "conf@1";
	210	conf@1 {
	211	kernel = "kernel@1";
	212	fdt = "fdt@1";
	213	};
	214	conf@1 {
	215	kernel = "kernel@2";
	216	fdt = "fdt@2";
	217	};
	218	};
	219	};
	220
	221	Since both kernels are signed it is easy for an attacker to add a new
	222	configuration 3 with kernel 1 and fdt 2:
	223
	224	configurations {
	225	default = "conf@1";
	226	conf@1 {
	227	kernel = "kernel@1";
	228	fdt = "fdt@1";
	229	};
230	conf@1 {
231	kernel = "kernel@2";
232	fdt = "fdt@2";
233	};
234	conf@3 {
235	kernel = "kernel@1";
236	fdt = "fdt@2";
237	};
238	};
239
240	With signed images, nothing protects against this. Whether it gains an
241	advantage for the attacker is debatable, but it is not secure.
242
243	To solved this problem, we support signed configurations. In this case it
244	is the configurations that are signed, not the image. Each image has its
245	own hash, and we include the hash in the configuration signature.
246
247	So the above example is adjusted to look like this:
248
249	/ {
250	images {
251	kernel@1 {
252	data = <data for kernel1>
253	hash@1 {
254	algo = "sha1";
255	value = <...kernel hash 1...>
256	};
257	};
258	kernel@2 {
259	data = <data for kernel2>
260	hash@1 {
261	algo = "sha1";
262	value = <...kernel hash 2...>
263	};
264	};
265	fdt@1 {
266	data = <data for fdt1>;
267	hash@1 {
268	algo = "sha1";
269	value = <...fdt hash 1...>
270	};
271	};
272	fdt@2 {
273	data = <data for fdt2>;
274	hash@1 {
275	algo = "sha1";
276	value = <...fdt hash 2...>
277	};
278	};
279	};
280	configurations {
281	default = "conf@1";
282	conf@1 {
283	kernel = "kernel@1";
284	fdt = "fdt@1";
285	signature@1 {
286	algo = "sha1,rsa2048";
287	value = <...conf 1 signature...>;
288	};
289	};
290	conf@2 {
291	kernel = "kernel@2";
292	fdt = "fdt@2";
293	signature@1 {
294	algo = "sha1,rsa2048";
295	value = <...conf 1 signature...>;
296	};
297	};
298	};
299	};
300
301
302	You can see that we have added hashes for all images (since they are no
303	longer signed), and a signature to each configuration. In the above example,
304	mkimage will sign configurations/conf@1, the kernel and fdt that are
305	pointed to by the configuration (/images/kernel@1, /images/kernel@1/hash@1,
306	/images/fdt@1, /images/fdt@1/hash@1) and the root structure of the image
307	(so that it isn't possible to add or remove root nodes). The signature is
308	written into /configurations/conf@1/signature@1/value. It can easily be
309	verified later even if the FIT has been signed with other keys in the
310	meantime.
311
312
3e569a6b SG	313	Verification
	314	------------
	315	FITs are verified when loaded. After the configuration is selected a list
	316	of required images is produced. If there are 'required' public keys, then
	317	each image must be verified against those keys. This means that every image
	318	that might be used by the target needs to be signed with 'required' keys.
	319
	320	This happens automatically as part of a bootm command when FITs are used.
	321
	322
	323	Enabling FIT Verification
	324	-------------------------
	325	In addition to the options to enable FIT itself, the following CONFIGs must
	326	be enabled:
	327
	328	CONFIG_FIT_SIGNATURE - enable signing and verfication in FITs
	329	CONFIG_RSA - enable RSA algorithm for signing
	330
21d29f7f HS	331	WARNING: When relying on signed FIT images with required signature check
	332	the legacy image format is default disabled by not defining
	333	CONFIG_IMAGE_FORMAT_LEGACY
3e569a6b SG	334
	335	Testing
	336	-------
	337	An easy way to test signing and verfication is to use the test script
	338	provided in test/vboot/vboot_test.sh. This uses sandbox (a special version
	339	of U-Boot which runs under Linux) to show the operation of a 'bootm'
	340	command loading and verifying images.
	341
	342	A sample run is show below:
	343
	344	$ make O=sandbox sandbox_config
	345	$ make O=sandbox
	346	$ O=sandbox ./test/vboot/vboot_test.sh
	347	Simple Verified Boot Test
	348	=========================
	349
	350	Please see doc/uImage.FIT/verified-boot.txt for more information
	351
646257d1	352	/home/hs/ids/u-boot/sandbox/tools/mkimage -D -I dts -O dtb -p 2000
3e569a6b	353	Build keys
646257d1	354	do sha1 test
3e569a6b SG	355	Build FIT with signed images
	356	Test Verified Boot Run: unsigned signatures:: OK
	357	Sign images
	358	Test Verified Boot Run: signed images: OK
	359	Build FIT with signed configuration
	360	Test Verified Boot Run: unsigned config: OK
	361	Sign images
	362	Test Verified Boot Run: signed config: OK
29a23f9d	363	check signed config on the host
ce1400f6	364	Signature check OK
29a23f9d HS	365	OK
29a23f9d HS	366	Test Verified Boot Run: signed config: OK
646257d1 HS	367	Test Verified Boot Run: signed config with bad hash: OK
	368	do sha256 test
	369	Build FIT with signed images
	370	Test Verified Boot Run: unsigned signatures:: OK
	371	Sign images
	372	Test Verified Boot Run: signed images: OK
	373	Build FIT with signed configuration
	374	Test Verified Boot Run: unsigned config: OK
	375	Sign images
	376	Test Verified Boot Run: signed config: OK
29a23f9d	377	check signed config on the host
ce1400f6	378	Signature check OK
29a23f9d HS	379	OK
29a23f9d HS	380	Test Verified Boot Run: signed config: OK
646257d1	381	Test Verified Boot Run: signed config with bad hash: OK
3e569a6b SG	382
	383	Test passed
	384
ce1400f6	385
3e569a6b SG	386	Future Work
	387	-----------
	388	- Roll-back protection using a TPM is done using the tpm command. This can
	389	be scripted, but we might consider a default way of doing this, built into
	390	bootm.
	391
	392
	393	Possible Future Work
	394	--------------------
	395	- Add support for other RSA/SHA variants, such as rsa4096,sha512.
	396	- Other algorithms besides RSA
	397	- More sandbox tests for failure modes
	398	- Passwords for keys/certificates
	399	- Perhaps implement OAEP
	400	- Enhance bootm to permit scripted signature verification (so that a script
	401	can verify an image but not actually boot it)
	402
	403
	404	Simon Glass
	405	[email protected]
	406	1-1-13