Hi Alex,
Thanks for the context! What are your plans for upstreaming your ECDSA signing implementation? I've currently dedicated the next four weeks to getting signing+verification implemented, so if you'd like a helping hand either with any leftover signing work or to get verification started I'm happy to collaborate.
All the best, Tim
-----Original Message----- From: Alex G. mr.nuke.me@gmail.com Sent: February 5, 2021 11:09 AM To: Simon Glass sjg@chromium.org; Tim Romanski t-tromanski@microsoft.com Cc: u-boot@lists.denx.de; Deskin Miller deskinm@microsoft.com; Dylan D'Silva ddsilva@microsoft.com Subject: [EXTERNAL] Re: U-Boot ECDSA Implementation Question
Hi Tim,
On 2/5/21 8:35 AM, Simon Glass wrote:
I'm a current intern at Microsoft, and one of my priorities is to enable ECDSA for U-Boot image signing/verification. Simon mentioned someone is already working on ECC, it would be great to get synced up with related progress. For signing, I will likely replicate the existing approach of using the openssl library. I'm aware that signing happens on a host machine and verification happens during boot, which implies verification should have a custom implementation to avoid the openssl overhead in the U-Boot binary. My thoughts are to copy an ECC verification implementation from a well-tested widely-used open source project. I was wondering, is U-Boot's current RSA verification copied from another project? If so, how are security patches between the two copies of code usually handled? I'm thinking of deriving from the ECDSA implementation currently in the Linux kernel, though I'd also appreciate suggestions if there's a better/more widely tested & used implementation.
[snip]
Alexandru Gagniuc, on cc, has been looking at implementing the signing side of this recently and has sent some patches that you could look at.
I hope I can save you some effort on the signing side. Generally, you have two types of signed images. The first is the signed bootloader (BL2 or FSBL in ARM terms). The other one is the signed Flattened Image Tree (FIT) that we use in u-boot. The first one is vendor-specific, so you'd usually use vendor tools or write your own. We use mkimage to deal with the latter.
I've implemented the signing part [1] for mkimage. mkimage has the ability to use hardware signing via the PKCS11 engine of openssl, which I did not implement. You can read more about it here [3].
The verification part is still being defined [4][5]. The idea is to define a UCLASS which abstracts the underlying implementation. For RSA, it's defined here [6].
My goal with ECDSA verification was to use the ROM API of the STM32MP1. This meant I don't have to write a software implementation of ECDSA. This would be useful in two ways. It would enable ECDSA verification on devices that don't support it in hardware, and would also allow us to add some unit tests for ECDSA.
I suspect what you could do from here, is try to build my branch with ECDSA signing, play around with mkimage, and let us know how we can point you to the correct documentation. There's a lot of it in doc/, but it's not always easy to find.
Alex
[1] https://nam06.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithub.com... [2] https://nam06.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithub.com... [3] https://nam06.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithub.com... [4] https://nam06.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithub.com... [5] https://nam06.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithub.com... [6] https://nam06.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithub.com...