Steve's blog

How did we do?

After a lot of prodding behind the scenes, Debian and many other distributions managed to get new shim binaries dual-signed with both the old and new CAs. The members of the shim-review team did a sterling job with reviews in the last few weeks. Since I started pushing people in May, we've had 21 reviews accepted successfully - see here for the list. Great stuff!

What's next?

We already have one of our new dual-signed shim binaries in place in Debian, in unstable and testing (Forky) right now.

OMG!!! Will all my existing Secure Boot machines stop booting?

Almost definitely not, no. The specification for UEFI Secure Boot expects that valid dates on certificates should not be enforced for signatures here. All that matters here is the signatures themselves. Modulo buggy firmware, existing signed binaries should continue just fine.

Isn't this is all a bit short notice?

Yes it is. :-( A common rule of thumb when deploying CA certificates is to start the process of replacement ("rollover") when a certificate reaches half of its lifetime. Unfortunately, Microsoft have done this very late. They generated new keys in 2023, but didn't start signing shim and other third-party software with the UEFI CA until October 2025.

How to make a dual-signed shim binary?

Microsoft only ship binaries with a single signature included. To make things work, extract those signatures using sbattach --detach (from the sbsigntools source package, available in most distributions. Then apply those signatures one at a time to your shim binary, using sbattach --attach. Simple, really.