Yes packages are reproduced and signed. I get that and this is fantastic. That is not the big gap I am talking about which is making sure the expressions themselves even use the correct sources and are not tampered with. Making sure the central signing key is not compromised is pretty critical too, but that can be mitigated with independent reproduction servers that also sign, requiring a minimum of 3 before a new package is trusted.
Arch also still has each maintainer sign the packages they maintain, and there is a similar approval process to earn enough trust in your keys to become a maintainer, so there is a decentralized web of trust. Then you add reproducible builds on top of that to almost complete the story.
Signed reviews would remove the remaining SPOFs in debian and arch but sadly no one does this. Nix however does not even allow -optional- key pinning or verify signatures of any authors that choose to sign expressions or their commits, so NixOS is way behind Arch and Debian in this respect.
Ah so you’re talking about the package sources (e.g. Nix files, PKGBUILD, etc.). I guess that’s closer to commit signing, I think? Well Nixpkgs maintainership is much more bazaar than cathedral, for better or worse, and that stymies some of that. However most Nixpkgs maintainers do not have commit access at all. Nixpkgs is at least moving the right direction (I think) by limiting the power of committers to submit changes without review. Should Nixpkgs committers sign their commits? Probably, yea.
As for Debian, maintainers must still all be part of the web of trust with an application process and a registered key in the web of trust to contribute packages. https://wiki.debian.org/DebianMaintainer#step_5_:_Keyring_up...
Arch also still has each maintainer sign the packages they maintain, and there is a similar approval process to earn enough trust in your keys to become a maintainer, so there is a decentralized web of trust. Then you add reproducible builds on top of that to almost complete the story.
Signed reviews would remove the remaining SPOFs in debian and arch but sadly no one does this. Nix however does not even allow -optional- key pinning or verify signatures of any authors that choose to sign expressions or their commits, so NixOS is way behind Arch and Debian in this respect.