AVP reference client, Python

A tiny, runnable reference client for the HTTP/JSON profile. It drives the full lifecycle against a running server so you can watch every operation happen end to end. The standard library for HTTP plus one dependency (cryptography, only for the Ed25519 challenge signature); the source is one file, client.py.

python -m venv .venv && . .venv/bin/activate   # optional; Windows: .venv\Scripts\activate
pip install -r requirements.txt
python client.py                                # drives the flow against http://localhost:8787
python -m py_compile client.py                  # syntax check
python -m unittest test_crypto.py -v            # vector tests (must all pass)

Requires Python 3.9+.

Point it at a different server with the AVP_SERVER_URL environment variable:

AVP_SERVER_URL=http://vault.example:8787 python client.py

You need a server running first. The sibling ../server is the obvious one:

cd ../server && pip install -r requirements.txt && python server.py

What it does

In one run, with two locally generated members (alice and bob):

1. Generate keypairs, each member is a fresh Ed25519 keypair (cryptography). The base64 raw 32-byte Ed25519 public key is the member id (SPEC section 2).
2. Authenticate, the challenge -> sign nonce -> token flow. The client signs the raw nonce bytes (base64-decoded), which is exactly what a conformant server verifies.
3. createRepo, alice creates a repo as its sole member.
4. pull, once at the known version (server reports unchanged, omits the envelope) and once from version 0 (server returns the current envelope).
5. push, writes a new payload version with optimistic concurrency, then deliberately re-pushes at a stale expected version to show the conflict response.
6. addMember, alice records bob’s member entry.
7. fetchMemberKey, looks bob’s entry back up by member id (URL-encoded, because base64 ids contain + / =).
8. bob pulls and decrypts, bob authenticates with his own keypair, pulls the shared repo, unwraps the data key from his member entry, and decrypts the payload, recovering exactly what alice stored.

Each step prints a one-line transcript entry.

The crypto is real

Unlike placeholder clients, this one does the real envelope work (SPEC sections 4-5) using the sibling crypto module:

• derives a per-repo symmetric data key,
• AES-256-GCM encrypts the alt payload, binding (repoId, payloadVersion, keyEpoch) into the AAD (SPEC section 4),
• wraps the data key to each member’s X25519 public key via X25519 + HKDF-SHA256, and unwraps it again on the receiving side.

Those constructions are checked byte-for-byte against the conformance vectors by test_crypto.py, so this client genuinely interoperates rather than only round-tripping its own placeholders.

What is simplified (do not ship this)

This example is illustrative, not production. Specifically:

• No TLS. It talks plain HTTP to localhost by default. A real client uses HTTPS; bearer tokens are credentials and the transport MUST be TLS (SPEC section 12).
• Single process, no persistence. It generates fresh keypairs each run and keeps no state.
• No key rotation on removal. The lifecycle here does not exercise removeMember; a real client rotates the key epoch and re-wraps the data key to the remaining members when someone leaves.
• No anti-MITM key-binding verification. A production client SHOULD (and, off a host it does not operate, MUST) verify MemberEntry.keyBindingSig before wrapping a data key to a served member entry (SPEC section 9). This example skips that step.