The Nix hash property on mkDerivation-alike function is an SRI of NAR (Nix Archive).
flowchart LR Store[/Nix Store/] --> NAR[Turn into NAR] NAR --> Hash[Hash using sha256/sha512] Hash --> SRI[Turn sha256/sha512 hash to SRI] SRI --> Result[/SRI string/]
In practice, it should look like this Nushell code below:
encode nar ./path # Encode ./path as a NAR
| hash sha256 -b # Hash using sha256
| encode base64 # SRI process: Encode hash as a base64
| ["sha256-" $in] | str join # SRI process: Complete the base64'd hash as SRI