Add PCF-SIG signing/verification to CLI tooling

Introduce a generic `pcf-sig` tool (crate tools/pcf-sig, lib pcf_sig_cli +
bin pcf-sig) for signing and verifying any PCF file with PCF-SIG (Ed25519):
keygen, incremental sign, verify with optional trust check, and key listing.
Signing is incremental by default — partitions already covered by a valid
signature from the same key are skipped — with --resign to force.

Wire PCF-SIG into the `pfs` CLI: keygen and verify-sig delegate to
pcf_sig_cli, and every mutating command (mkfs/mkdir/put/mv/rm/create/update)
accepts --key to auto-sign after its commit.

Because PFS-MS is append-only with a backward-linked session chain, naively
appending signature partitions corrupts the chain. Signing a PFS-MS file is
therefore committed as a dedicated signature session (pfs-ms sign_archive),
covering content and node records; the generic pcf-sig sign refuses PFS-MS
files and points to `pfs sign`.

Includes roundtrip/incremental/tamper/refusal tests for both crates, a
dedicated CI workflow, release-binary packaging for pcf-sig, and README docs.

Author: claude

.github/workflows/build-binaries.yml

@@ -88,6 +88,7 @@ jobs:
         run: |
           cargo build --release --target ${{ matrix.target }} -p pcf-debug
           cargo build --release --target ${{ matrix.target }} -p pcf-compact
+          cargo build --release --target ${{ matrix.target }} -p pcf-sig-cli --bin pcf-sig
           cargo build --release --target ${{ matrix.target }} -p pfs-ms --bin pfs
 
       - name: Build (macOS universal2)
@@ -97,6 +98,7 @@ jobs:
           for t in ${{ matrix.macos-targets }}; do
             cargo build --release --target "$t" -p pcf-debug
             cargo build --release --target "$t" -p pcf-compact
+            cargo build --release --target "$t" -p pcf-sig-cli --bin pcf-sig
             cargo build --release --target "$t" -p pfs-ms --bin pfs
           done
           mkdir -p target/universal2-apple-darwin/release
@@ -106,11 +108,15 @@ jobs:
           lipo -create -output target/universal2-apple-darwin/release/pcf-compact \
             target/x86_64-apple-darwin/release/pcf-compact \
             target/aarch64-apple-darwin/release/pcf-compact
+          lipo -create -output target/universal2-apple-darwin/release/pcf-sig \
+            target/x86_64-apple-darwin/release/pcf-sig \
+            target/aarch64-apple-darwin/release/pcf-sig
           lipo -create -output target/universal2-apple-darwin/release/pfs \
             target/x86_64-apple-darwin/release/pfs \
             target/aarch64-apple-darwin/release/pfs
           file target/universal2-apple-darwin/release/pcf-debug
           file target/universal2-apple-darwin/release/pcf-compact
+          file target/universal2-apple-darwin/release/pcf-sig
           file target/universal2-apple-darwin/release/pfs
 
       - name: Stage and archive (unix)
@@ -120,7 +126,7 @@ jobs:
           VERSION='${{ needs.resolve-version.outputs.version }}'
           TARGET='${{ matrix.target }}'
           mkdir -p staging
-          for bin in pcf-debug pcf-compact pfs; do
+          for bin in pcf-debug pcf-compact pcf-sig pfs; do
             STAGE="staging/${bin}-${VERSION}-${TARGET}"
             mkdir -p "$STAGE"
             cp "target/${TARGET}/release/${bin}" "$STAGE/${bin}"
@@ -136,7 +142,7 @@ jobs:
           $version = '${{ needs.resolve-version.outputs.version }}'
           $target  = '${{ matrix.target }}'
           New-Item -ItemType Directory -Force staging | Out-Null
-          foreach ($bin in @('pcf-debug', 'pcf-compact', 'pfs')) {
+          foreach ($bin in @('pcf-debug', 'pcf-compact', 'pcf-sig', 'pfs')) {
             $stage = "staging/$bin-$version-$target"
             New-Item -ItemType Directory -Force $stage | Out-Null
             Copy-Item "target/$target/release/$bin.exe" "$stage/$bin.exe"

.github/workflows/ci-pcf-sig.yml

@@ -0,0 +1,55 @@
+name: CI / Rust (pcf-sig CLI)
+
+on:
+  push:
+    branches: [master]
+  pull_request:
+    branches: [master]
+
+env:
+  CARGO_TERM_COLOR: always
+  RUSTFLAGS: "-D warnings"
+
+defaults:
+  run:
+    working-directory: tools/pcf-sig
+
+jobs:
+  fmt:
+    name: rustfmt
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: dtolnay/rust-toolchain@stable
+        with:
+          components: rustfmt
+      - run: cargo fmt --all -- --check
+
+  clippy:
+    name: clippy
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: dtolnay/rust-toolchain@stable
+        with:
+          components: clippy
+      - uses: Swatinem/rust-cache@v2
+        with:
+          workspaces: tools/pcf-sig
+      - run: cargo clippy --all-targets --all-features -- -D warnings
+
+  test:
+    name: test (${{ matrix.os }})
+    runs-on: ${{ matrix.os }}
+    strategy:
+      fail-fast: false
+      matrix:
+        os: [ubuntu-latest, macos-latest, windows-latest]
+    steps:
+      - uses: actions/checkout@v4
+      - uses: dtolnay/rust-toolchain@stable
+      - uses: Swatinem/rust-cache@v2
+        with:
+          workspaces: tools/pcf-sig
+      - run: cargo build --verbose
+      - run: cargo test --all-targets --verbose

Cargo.toml

@@ -6,4 +6,5 @@ members = [
     "reference/PCF-SIG-v1.0",
     "tools/pcf-debug",
     "tools/pcf-compact",
+    "tools/pcf-sig",
 ]

reference/PCF-SIG-v1.0/README.md

@@ -75,6 +75,22 @@ for report in verify_all_with_recheck(&mut c)? {
 # Ok::<(), pcf_sig::Error>(())
 ```
 
+## Command-line tool
+
+A ready-made CLI lives in [`tools/pcf-sig`](../../tools/pcf-sig) (`pcf-sig`),
+built on this crate:
+
+```sh
+pcf-sig keygen id.key id.pub          # 32-byte raw Ed25519 seed + public key
+pcf-sig sign   file.pcf --key id.key  # incremental by default; --resign to redo
+pcf-sig verify file.pcf --key id.pub  # per-signature / per-partition report
+pcf-sig keys   file.pcf               # list embedded PCFSIG_KEY fingerprints
+```
+
+A PFS-MS archive is a PCF file, so `pcf-sig verify`/`keys` work on it directly;
+to *sign* a PFS-MS file use `pfs sign`, which commits the signature as a PFS
+session (see [`reference/PFS-MS-v1.0`](../PFS-MS-v1.0)).
+
 ## Trust patterns
 
 The profile describes one non-X.509 way for an application to express trust

reference/PFS-MS-v1.0/Cargo.toml

@@ -38,3 +38,13 @@ flate2 = { version = "1", default-features = false, features = ["rust_backend"]
 
 # Portable file modification-time setting for the directory-import/extract tools.
 filetime = "0.2"
+
+# Shared PCF-SIG command-line logic, so `pfs` can run keygen / verify-sig using
+# exactly the same implementation as the standalone `pcf-sig` tool.
+pcf-sig-cli = { path = "../../tools/pcf-sig", version = "0.0.8" }
+
+# The PCF-SIG signing primitives. Signing a PFS-MS file cannot simply append
+# partitions (that would break the backward-linked session chain); instead the
+# PCFSIG_KEY / PCFSIG_SIG partitions are committed as a dedicated PFS session
+# (see `src/sign.rs`), built from these primitives.
+pcf-sig = { path = "../PCF-SIG-v1.0", version = "0.0.8" }

reference/PFS-MS-v1.0/README.md

@@ -136,6 +136,37 @@ on extract; pass `--no-metadata` (on either side) to skip this, and `--store` to
 disable compression. Symlinks and other non-regular files are skipped with a
 warning.
 
+### Signing (PCF-SIG)
+
+`pfs` can sign archives with [PCF-SIG](../PCF-SIG-v1.0) (Ed25519). Because
+PFS-MS is append-only with a backward-linked session chain, a signature is
+**committed as its own PFS session** carrying the `PCFSIG_KEY` / `PCFSIG_SIG`
+partitions — not appended out of band — so `verify` keeps working.
+
+```
+# Generate a keypair (delegates to the pcf-sig tool).
+cargo run --bin pfs -- keygen id.key id.pub
+
+# Sign content + node records not yet signed by this key (incremental).
+cargo run --bin pfs -- sign       fs.pfs --key id.key          # no-op if nothing new
+cargo run --bin pfs -- sign       fs.pfs --key id.key --resign # re-sign everything
+
+# Verify embedded signatures (optionally assert a trusted public key).
+cargo run --bin pfs -- verify-sig fs.pfs --key id.pub
+```
+
+Every mutating command (`mkfs`, `mkdir`, `put`, `mv`, `rm`, `create`, `update`)
+also accepts `--key <priv>` to **auto-sign** right after its commit, so each
+operation adds one signature covering just the partitions it introduced:
+
+```
+cargo run --bin pfs -- mkfs fs.pfs --key id.key
+echo hi | cargo run --bin pfs -- put fs.pfs hello.txt - --key id.key
+```
+
+Signatures cover file content and node records; PFS-MS's own inter-session hash
+chain (checked by `verify`) already makes session records tamper-evident.
+
 ## Layout
 
 ```