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diff --git a/tvix/store/protos/pathinfo.proto b/tvix/store/protos/pathinfo.proto
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+++ b/tvix/store/protos/pathinfo.proto
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+// SPDX-License-Identifier: MIT
+// Copyright © 2022 The Tvix Authors
+syntax = "proto3";
+
+package tvix.store.v1;
+
+import "tvix/castore/protos/castore.proto";
+
+option go_package = "code.tvl.fyi/tvix/store-go;storev1";
+
+// PathInfo shows information about a Nix Store Path.
+// That's a single element inside /nix/store.
+message PathInfo {
+  // The path can be a directory, file or symlink.
+  tvix.castore.v1.Node node = 1;
+
+  // List of references (output path hashes)
+  // This really is the raw *bytes*, after decoding nixbase32, and not a
+  // base32-encoded string.
+  repeated bytes references = 2;
+
+  // see below.
+  NARInfo narinfo = 3;
+}
+
+// Represents a path in the Nix store (a direct child of STORE_DIR).
+// It is commonly formatted by a nixbase32-encoding the digest, and
+// concatenating the name, separated by a `-`.
+message StorePath {
+  // The string after digest and `-`.
+  string name = 1;
+
+  // The digest (20 bytes).
+  bytes digest = 2;
+}
+
+// Nix C++ uses NAR (Nix Archive) as a format to transfer store paths,
+// and stores metadata and signatures in NARInfo files.
+// Store all these attributes in a separate message.
+//
+// This is useful to render .narinfo files to clients, or to preserve/validate
+// these signatures.
+// As verifying these signatures requires the whole NAR file to be synthesized,
+// moving to another signature scheme is desired.
+// Even then, it still makes sense to hold this data, for old clients.
+message NARInfo {
+  // This represents a (parsed) signature line in a .narinfo file.
+  message Signature {
+    string name = 1;
+    bytes data = 2;
+  }
+
+  // This size of the NAR file, in bytes.
+  uint64 nar_size = 1;
+
+  // The sha256 of the NAR file representation.
+  bytes nar_sha256 = 2;
+
+  // The signatures in a .narinfo file.
+  repeated Signature signatures = 3;
+
+  // A list of references. To validate .narinfo signatures, a fingerprint needs
+  // to be constructed.
+  // This fingerprint doesn't just contain the hashes of the output paths of all
+  // references (like PathInfo.references), but their whole (base)names, so we
+  // need to keep them somewhere.
+  repeated string reference_names = 4;
+
+  // The StorePath of the .drv file producing this output.
+  // The .drv suffix is omitted in its `name` field.
+  StorePath deriver = 5;
+
+  // The CA field in the .narinfo.
+  // Its textual representations seen in the wild are one of the following:
+  //  - `fixed:r:sha256:1gcky5hlf5vqfzpyhihydmm54grhc94mcs8w7xr8613qsqb1v2j6`
+  //    fixed-output derivations using "recursive" `outputHashMode`.
+  //  - `fixed:sha256:19xqkh72crbcba7flwxyi3n293vav6d7qkzkh2v4zfyi4iia8vj8
+  //    fixed-output derivations using "flat" `outputHashMode`
+  //  - `text:sha256:19xqkh72crbcba7flwxyi3n293vav6d7qkzkh2v4zfyi4iia8vj8`
+  //    Text hashing, used for uploaded .drv files and outputs produced by
+  //    builtins.toFile.
+  //
+  // Semantically, they can be split into the following components:
+  //  - "content address prefix". Currently, "fixed" and "text" are supported.
+  //  - "hash mode". Currently, "flat" and "recursive" are supported.
+  //  - "hash type". The underlying hash function used.
+  //    Currently, sha1, md5, sha256, sha512.
+  //  - "digest". The digest itself.
+  //
+  // There are some restrictions on the possible combinations.
+  // For example, `text` and `fixed:recursive` always imply sha256.
+  //
+  // We use an enum to encode the possible combinations, and optimize for the
+  // common case, `fixed:recursive`, identified as `NAR_SHA256`.
+  CA ca = 6;
+
+  message CA {
+    enum Hash {
+      // produced when uploading fixed-output store paths using NAR-based
+      // hashing (`outputHashMode = "recursive"`).
+      NAR_SHA256 = 0;
+      NAR_SHA1 = 1;
+      NAR_SHA512 = 2;
+      NAR_MD5 = 3;
+
+      // Produced when uploading .drv files or outputs produced by
+      // builtins.toFile.
+      // Produces equivalent digests as FLAT_SHA256, but is a separate
+      // hashing type in Nix, affecting output path calculation.
+      TEXT_SHA256 = 4;
+
+      // Produced when using fixed-output derivations with
+      // `outputHashMode = "flat"`.
+      FLAT_SHA1 = 5;
+      FLAT_MD5 = 6;
+      FLAT_SHA256 = 7;
+      FLAT_SHA512 = 8;
+
+      // TODO: what happens in Rust if we introduce a new enum kind here?
+    }
+
+    // The hashing type used.
+    Hash type = 1;
+
+    // The digest, in raw bytes.
+    bytes digest = 2;
+  }
+}