Hi Joel,
On Mon, Dec 17, 2012 at 9:11 PM, Fernandes, Joel A joelagnel@ti.com wrote:
Hi,
Can anyone comment on what has been discussed about a framework for secure boot and authentication, if there has been such a discussion, in the community?
I have some U-boot code that is based off of a slightly older U-boot which does authentication and/or decryption. The main code that does the cryptography is in the ROM of the SoC. However, I'm sure there will be other U-boot developers requiring the crypto algorithms itself to be supported.
My questions are : (1) Would a general framework for performing authentication and/or decryption of signed and/or encrypted images be useful for U-boot? These operations seem to make a lot of sense for a bootloader.
(2) Does such a framework make sense for any of your usecase(s)?
(3) Has there been any work or discussions of coming up with such a framework for U-boot?
We have created a secure boot system on top of U-Boot - it is in the Chromium tree if you want to take a look. Three ChromeOS devices have shipped with this so far. However it is not really suitable for generic upstream use, so...
There have been some discussions lately on the list about using the FIT format to hold an image which can then be verified using a public key. We have put together a possible design for this and I am working on this as I make time.
I imagine a framework like this will atleast consist of:
- General purposes cryptographic functions in a library (which we might
not need for our case), some light weight crypto library. 2. Hooks for board/Soc-specific functions that call into the general crypto lib and do any other board/SoC-specific stuff. 3. General commands (in a cmd_crpto.c) that calls into the callbacks mentioned in 2. for encryption and verification of an image already in memory. (making it commands can allow us to leave bootm alone and do the inplace decryption/verification independently - however for SPL, we don't need the commands and call into 2. directly). 4. Abstract any other change(s) to common boot code in a common place.
Yes that seems reasonable.
A very basic hashing framework recently went into U-Boot, and this can be used to plumb in SOC hashing acceleration code. I suspect we will do the same with RSA, supporting a few different key lengths and associated padding.
My plan at present is roughly (and in short order) to:
1. Define how signatures are represented in FIT 2. Enhance mkimage to sign an image or a configuration (consisting of image +fdt, for example) 3. Enhance FIT command to verify an image given a public key 4. Support checking of version information against a TPM rollback counter 5. Work this into the bootm code 6. Add RSA2048/4096
This would provide the pieces for verified boot, if not a full implementation. It should then be possible to do verified boot with a U-Boot script. If we get this far then it will provide a good basis for more advanced efforts.
Regards, Simon
Let me know your suggestions, thanks.
Regards, Joel _______________________________________________ U-Boot mailing list U-Boot@lists.denx.de http://lists.denx.de/mailman/listinfo/u-boot