This solves all our problems and makes download-nar.scm useless. As an added bonus, it provides a improves the UI since we now always see: --8<---------------cut here---------------start------------->8--- 0.1 MB will be downloaded: /gnu/store/plx9848n6waj6zghn3d54ybx8ihcn23k-guile-git-0.0-4.951a32c-checkout --8<---------------cut here---------------end--------------->8--- … instead of: --8<---------------cut here---------------start------------->8--- The following derivation will be built: /gnu/store/y86rlb6pdm35im7q02y6479ca84zwylz-guile-git-000.0-4.951a32c-checkout.drv --8<---------------cut here---------------end--------------->8--- The downside is that it still requires one to authorize the server’s key, although it’s in theory unnecessary since it’s content addressed. I’m not sure how to solve that because ‘guix substitute’ doesn’t know that it’s substituting a fixed-output derivation. I suppose we’d need to modify the “protocol” between guix-daemon and ‘guix substitute’. Thoughts? Ludo’.