175 lines
6.8 KiB
Markdown
175 lines
6.8 KiB
Markdown
# claude-tokenization-proxy
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A local Data Loss Prevention (DLP) proxy that sits between `claude-code` and the
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Anthropic API. It scans outgoing requests for secrets with
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[GitGuardian's `ggshield`](https://github.com/GitGuardian/ggshield), swaps each
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secret for an opaque placeholder token before it leaves your machine, then
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restores the real secret in the streamed response on the fly — so Claude never
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sees your secrets but tooling that echoes a placeholder still gets the real
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value back.
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```
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claude-code ──POST /v1/messages──► proxy ──redacted──► api.anthropic.com
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(ggshield scan, secret → <<<gg_token_…>>>) │
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claude-code ◄──SSE (detokenized)─── proxy ◄──SSE stream──┘
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(real secret ← <<<gg_token_…>>>, streaming)
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```
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## How it works
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1. **Request interception** — the JSON body of `POST /v1/messages` is scanned by
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`ggshield`. Every detected secret is encrypted with **AES-256-GCM** under a
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persistent master key and replaced with a self-contained
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`<<<gg_token_[hex]>>>` placeholder, where the hex payload is `IV ++ authTag ++ ciphertext`. No server-side mapping is kept — the token carries everything
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needed to restore it (`src/tokenize.ts`, `src/store.ts`). The redacted body is
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forwarded upstream.
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2. **Streaming detokenization** — the response is piped through a stateful
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`Transform` (`src/detokenize.ts`) that finds placeholders, decrypts the hex
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payload, and substitutes the original secret back. For SSE streams it parses
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`content_block_delta` events and reassembles the reconstructed text, because
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the model emits a long placeholder fragmented across many deltas
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(`…"text":"<<<gg_to"}` / `{"text":"ken_abc>>>"…`) with event framing wedged
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between the fragments — a raw byte scan can't bridge that. Plain JSON
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responses, where the token is contiguous, take a simpler direct byte scan.
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The proxy is **stateless**: tokens are cryptographically self-contained, so they
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resolve correctly even after a restart or when replaying older chat histories.
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The only persistent state is the 256-bit master key, generated on first run and
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stored `0600` at `~/.config/claude-tokenization-proxy/master.key` (override with
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`GG_MASTER_KEY_FILE`). Anyone with that key file can decrypt captured tokens —
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treat it like any other secret, and deleting it makes existing tokens
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unrecoverable.
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## Requirements
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* **Node.js ≥ 23.6** (the proxy runs TypeScript directly via Node's built-in
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type stripping — no build step, no `ts-node`/`tsx`). On Node 22.6–23.5 run
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with `node --experimental-strip-types src/index.ts`.
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* **`ggshield`** on your `PATH` and authenticated (`ggshield auth login`). If
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`ggshield` is missing or errors, the proxy logs a warning and forwards traffic
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**unredacted** (fail-open) — it never blocks your requests.
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## Setup
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```bash
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npm install # dev-only deps (TypeScript types); not needed to run
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npm start # starts the proxy on http://127.0.0.1:8080
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```
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Point `claude-code` at the proxy:
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```bash
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export ANTHROPIC_BASE_URL=http://127.0.0.1:8080
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claude
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```
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For the [fish shell](https://fishshell.com/):
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```fish
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set -gx ANTHROPIC_BASE_URL http://localhost:8080
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claude
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```
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That's the only change `claude-code` needs — it keeps using your normal
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`ANTHROPIC_API_KEY` / `x-api-key`, which the proxy forwards untouched.
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## Configuration
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| Env var | Default | Purpose |
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| ------------------------- | ------------------- | ------------------------------- |
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| `PORT` | `8080` | Port the proxy listens on |
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| `ANTHROPIC_UPSTREAM_HOST` | `api.anthropic.com` | Upstream API host to forward to |
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## Tell Claude to leave the tokens alone
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So the model preserves placeholders verbatim (e.g. when writing them to files),
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copy [`templates/CLAUDE.md`](templates/CLAUDE.md) into the `CLAUDE.md` of any
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project you run `claude-code` in:
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```markdown
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# Security Constraints
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Do not modify, remove, or evaluate strings formatted as `<<<gg_token_[a-f0-9]+>>>`.
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Treat them as opaque identifiers and preserve them exactly as they appear when
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writing or reading files.
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```
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## Run at boot/login (systemd user service)
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[`templates/claude-tokenization-proxy.service`](templates/claude-tokenization-proxy.service)
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is a ready-to-use systemd **user** unit that runs the proxy in the background and
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restarts it on failure.
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```bash
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# 1. Install the unit
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mkdir -p ~/.config/systemd/user
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cp templates/claude-tokenization-proxy.service ~/.config/systemd/user/
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# 2. Edit WorkingDirectory= to point at your clone (and the node path if you
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# use a version manager like nvm/fnm/asdf — see the comments in the unit)
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$EDITOR ~/.config/systemd/user/claude-tokenization-proxy.service
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# 3. Enable + start it
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systemctl --user daemon-reload
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systemctl --user enable --now claude-tokenization-proxy.service
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# Check status / logs
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systemctl --user status claude-tokenization-proxy.service
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journalctl --user -u claude-tokenization-proxy.service -f
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```
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A user service starts when **you** log in. To keep it running at boot before
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any login (and after you log out), enable lingering for your account:
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```bash
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sudo loginctl enable-linger "$USER"
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```
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## Permanently point claude-code at the proxy
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Setting `ANTHROPIC_BASE_URL` per shell (as in [Setup](%23setup)) only lasts for
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that session. To make it stick:
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* **fish** — set a universal variable once; it persists across sessions:
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```fish
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set -Ux ANTHROPIC_BASE_URL http://localhost:8080
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```
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* **bash/zsh** — add the export to your shell rc (or `~/.profile` for all shells):
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```bash
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echo 'export ANTHROPIC_BASE_URL=http://localhost:8080' >> ~/.bashrc
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```
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* **All processes in a graphical session** (works regardless of shell) — drop
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it in systemd's user environment:
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```bash
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mkdir -p ~/.config/environment.d
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echo 'ANTHROPIC_BASE_URL=http://localhost:8080' >> ~/.config/environment.d/claude.conf
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```
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Takes effect on next login.
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## Scripts
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| Command | What it does |
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| ------------------- | --------------------------------------------- |
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| `npm start` | Run the proxy |
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| `npm run dev` | Run with `--watch` (restarts on file changes) |
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| `npm test` | Run the detokenizer state-machine self-check |
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| `npm run typecheck` | Type-check the source with `tsc --noEmit` |
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## Limitations
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* Detection is only as good as `ggshield`. It catches known secret patterns and
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generic high-entropy strings, not arbitrary sensitive prose.
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* Tokens are decryptable by anyone holding the master key file. Multiple proxy
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instances must share the same `master.key` to resolve each other's tokens.
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## License
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Copyright (C) 2026 Rootiest. Licensed under the
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[GNU Affero General Public License v3.0 or later](LICENSE).
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