unforgeable.nix

/* Primitives for unforgeable values in Nix. As long as the make-unforgeable primitive isn't
 * available to arbitrary expressions (e.g. it's defined in a let within your entry point
 * and only made available through a more constrained interface), you can use this to build
 * general functionality to enforcethat some value must have been created by some trusted
 * component.
 * 
 * This is stupidly hacky and relies on a number of questionable assumptions.
 */
rec {
  make-unforgeable = x: { value = x; };
  read-unforgeable = let
    reference = builtins.unsafeGetAttrPos "value" (make-unforgeable null);
  in x: if reference == builtins.unsafeGetAttrPos "value" x
    then x.value
  else throw "Forgery!";
}