339 lines
12 KiB
Python
339 lines
12 KiB
Python
"""ZKAC server: all traffic over a single encrypted, server-authenticated channel.
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Every connection performs an anonymous handshake (X25519 + Schnorr server
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identity proof). The first encrypted frame selects the mode:
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{"op": "mgmt"} management commands (create_registry, post_grant, ...)
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{"op": "auth", "registry_id": hex, "bbs_auth_b64": ...} role authentication
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The server stores only cryptographically verified opaque blobs:
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<data_dir>/server_key.json Schnorr keypair
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<data_dir>/registries/<rid>.state raw RegistryState bytes
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<data_dir>/registries/<rid>.cert raw state cert bytes
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<data_dir>/mailbox/grants_pool.json anonymous append-only grant pool (PIR-friendly)
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Grants are **not** keyed by recipient public key on the server; delivery uses a
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shared pool with **two-server XOR PIR** only: clients issue ``pir_fold`` queries
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to two replicas with identical pools (``mail_pool_len`` + ``pir_fold``). There
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is no bulk grant export command.
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"""
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from __future__ import annotations
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import base64
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import json
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import os
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import socket
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import threading
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import traceback
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from pathlib import Path
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import zkac
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from zkac.tcp import FramedSession, server_handshake_anon
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from . import pir
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def _b64(data: bytes) -> str:
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return base64.b64encode(data).decode()
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def _unb64(s: str) -> bytes:
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return base64.b64decode(s)
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# ── Opaque server storage ─────────────────────────────────────────────
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class _ServerStore:
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"""Thread-safe, opaque persistence for registries and anonymous grant pool."""
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def __init__(self, data_dir: Path):
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self._dir = data_dir
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self._reg_dir = data_dir / "registries"
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self._mbox_dir = data_dir / "mailbox"
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self._pool_path = self._mbox_dir / "grants_pool.json"
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self._reg_dir.mkdir(parents=True, exist_ok=True)
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self._mbox_dir.mkdir(parents=True, exist_ok=True)
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self._lock = threading.Lock()
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self._migrate_legacy_mailbox()
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# ── server key ────────────────────────────────────────────────────
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def load_or_create_keypair(self) -> zkac.Keypair:
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kf = self._dir / "server_key.json"
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if kf.exists():
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data = json.loads(kf.read_text())
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return zkac.Keypair.from_secret_key(_unb64(data["secret_b64"]))
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kp = zkac.Keypair()
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kf.write_text(json.dumps({
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"secret_b64": _b64(kp.secret_key_bytes()),
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"public_b64": _b64(kp.public_key().to_bytes()),
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}, indent=2))
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return kp
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# ── registries ────────────────────────────────────────────────────
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def save_registry(self, rid_hex: str, state_bytes: bytes, cert_bytes: bytes):
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with self._lock:
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(self._reg_dir / f"{rid_hex}.state").write_bytes(state_bytes)
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(self._reg_dir / f"{rid_hex}.cert").write_bytes(cert_bytes)
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def load_all_registries(self, mgr: zkac.RegistryManager) -> int:
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count = 0
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for p in sorted(self._reg_dir.glob("*.state")):
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rid_hex = p.stem
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cert_path = self._reg_dir / f"{rid_hex}.cert"
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if not cert_path.exists():
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continue
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try:
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mgr.create(p.read_bytes(), cert_path.read_bytes())
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count += 1
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except Exception as exc:
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print(f"[server] skip registry {rid_hex}: {exc}")
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return count
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# ── legacy per-recipient mailbox → anonymous pool ─────────────────
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def _migrate_legacy_mailbox(self):
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if self._pool_path.exists():
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return
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records: list[dict] = []
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for p in sorted(self._mbox_dir.glob("*.json")):
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if p.name == "grants_pool.json":
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continue
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try:
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entries = json.loads(p.read_text())
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for e in entries:
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if "claimed" not in e:
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e["claimed"] = False
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records.append(e)
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except Exception as exc:
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print(f"[server] skip legacy mailbox {p.name}: {exc}")
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try:
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p.unlink()
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except OSError:
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pass
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if records:
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self._pool_path.write_text(
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json.dumps({"version": 1, "records": records}, indent=2)
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)
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def _load_pool(self) -> list[dict]:
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if not self._pool_path.exists():
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return []
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data = json.loads(self._pool_path.read_text())
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return data.get("records", [])
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def _save_pool(self, records: list[dict]):
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self._pool_path.write_text(
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json.dumps({"version": 1, "records": records}, indent=2)
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)
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# ── anonymous grant pool ─────────────────────────────────────────
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def post_grant(self, entry: dict) -> tuple[str, int]:
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grant_id = os.urandom(16).hex()
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row = {"grant_id": grant_id, "claimed": False, **entry}
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try:
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pir.pad_grant_record(row)
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except ValueError as exc:
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raise ValueError(
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f"grant entry too large for PIR record size ({pir.PIR_RECORD_BYTES} bytes): {exc}"
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) from exc
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with self._lock:
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records = self._load_pool()
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pool_index = len(records)
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records.append(row)
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self._save_pool(records)
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return grant_id, pool_index
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def pool_len(self) -> tuple[int, int]:
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with self._lock:
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n = len(self._load_pool())
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return n, pir.PIR_RECORD_BYTES
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def pir_fold(self, indices: list[int]) -> bytes:
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with self._lock:
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records = self._load_pool()
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uniq = sorted(set(indices))
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for i in uniq:
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if not (0 <= i < len(records)):
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raise ValueError("pir_fold index out of range")
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chunks = [pir.pad_grant_record(records[i]) for i in uniq]
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return pir.xor_bytes_many(chunks)
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def claim_grant(self, grant_id: str) -> dict | None:
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with self._lock:
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records = self._load_pool()
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for i, e in enumerate(records):
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if e["grant_id"] == grant_id and not e.get("claimed", False):
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e["claimed"] = True
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records[i] = e
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self._save_pool(records)
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return dict(e)
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return None
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# ── Command dispatch (inside encrypted session) ──────────────────────
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def _dispatch(cmd: dict, mgr: zkac.RegistryManager, store: _ServerStore,
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server_pk_b64: str, transcript_hash: bytes) -> dict:
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try:
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action = cmd.get("cmd")
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if action == "server_info":
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return {"ok": True, "server_public_key_b64": server_pk_b64}
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if action == "create_registry":
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state_bytes = _unb64(cmd["state_bytes_b64"])
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state_cert = _unb64(cmd["state_cert_b64"])
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rid = mgr.create(state_bytes, state_cert)
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store.save_registry(rid.hex(), state_bytes, state_cert)
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return {"ok": True, "registry_id": rid.hex()}
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if action == "get_registry":
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rid = bytes.fromhex(cmd["registry_id"])
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state_bytes, state_cert = mgr.get(rid)
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return {
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"ok": True,
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"state_bytes_b64": _b64(state_bytes),
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"state_cert_b64": _b64(state_cert),
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}
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if action == "update_registry":
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rid = bytes.fromhex(cmd["registry_id"])
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state_bytes = _unb64(cmd["state_bytes_b64"])
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state_cert = _unb64(cmd["state_cert_b64"])
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mgr.update(rid, state_bytes, state_cert)
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store.save_registry(cmd["registry_id"], state_bytes, state_cert)
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return {"ok": True}
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if action == "post_grant":
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rid = bytes.fromhex(cmd["registry_id"])
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proof = _unb64(cmd["admin_proof_b64"])
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if not mgr.verify_admin(rid, proof, transcript_hash):
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return {"error": "admin proof failed"}
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entry = {
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"eph_pk_b64": cmd["eph_pk_b64"],
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"ciphertext_b64": cmd["ciphertext_b64"],
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}
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gid, pool_index = store.post_grant(entry)
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return {"ok": True, "grant_id": gid, "pool_index": pool_index}
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if action == "mail_pool_len":
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n, rec_b = store.pool_len()
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return {"ok": True, "n": n, "record_bytes": rec_b}
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if action == "pir_fold":
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raw = store.pir_fold(list(cmd.get("indices", [])))
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return {"ok": True, "xor_b64": _b64(raw)}
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if action == "claim_grant":
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entry = store.claim_grant(cmd["grant_id"])
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if entry is None:
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return {"error": "grant not found"}
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return {"ok": True, "grant": entry}
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return {"error": f"unknown command: {action}"}
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except Exception as exc:
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return {"error": str(exc)}
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# ── Connection handler ────────────────────────────────────────────────
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def _handle_conn(conn: socket.socket, addr: tuple, node: zkac.Node,
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mgr: zkac.RegistryManager, store: _ServerStore,
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server_pk_b64: str):
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peer = f"{addr[0]}:{addr[1]}"
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try:
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session = server_handshake_anon(conn, node)
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framed = FramedSession(conn, session)
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transcript_hash = bytes(session.transcript_hash())
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hello = json.loads(framed.recv())
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op = hello.get("op")
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if op == "mgmt":
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while True:
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try:
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data = framed.recv()
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except (ConnectionError, OSError):
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break
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cmd = json.loads(data)
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resp = _dispatch(cmd, mgr, store, server_pk_b64, transcript_hash)
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framed.send(json.dumps(resp).encode())
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elif op == "auth":
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registry_id = bytes.fromhex(hello["registry_id"])
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role_id = bytes.fromhex(hello["role_id"])
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proof_bytes = _unb64(hello["bbs_auth_b64"])
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ok = mgr.verify_presentation(
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registry_id, role_id, proof_bytes, transcript_hash,
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)
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if not ok:
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framed.send(json.dumps({"error": "auth failed"}).encode())
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return
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resp = {
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"status": "authenticated",
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"registry_id": registry_id.hex(),
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"role_id": role_id.hex(),
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}
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framed.send(json.dumps(resp).encode())
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# keep session open for app traffic
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while True:
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try:
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data = framed.recv()
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except (ConnectionError, OSError):
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break
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framed.send(data)
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else:
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framed.send(json.dumps({"error": f"unknown op: {op}"}).encode())
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except (ConnectionError, BrokenPipeError, OSError):
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pass
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except Exception as exc:
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print(f"[server] {peer} error: {exc}")
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traceback.print_exc()
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finally:
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conn.close()
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# ── Public entry point ────────────────────────────────────────────────
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def serve(data_dir: str, host: str = "127.0.0.1", port: int = 9800):
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dd = Path(data_dir)
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dd.mkdir(parents=True, exist_ok=True)
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store = _ServerStore(dd)
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kp = store.load_or_create_keypair()
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server_pk_b64 = _b64(kp.public_key().to_bytes())
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node = zkac.Node(kp)
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mgr = zkac.RegistryManager()
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n = store.load_all_registries(mgr)
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print(f"server public key: {_unb64(server_pk_b64).hex()}")
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print(f"loaded {n} registries")
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print(f"listening on {host}:{port}")
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sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
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sock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
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sock.bind((host, port))
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sock.listen(8)
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try:
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while True:
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conn, addr = sock.accept()
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threading.Thread(
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target=_handle_conn,
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args=(conn, addr, node, mgr, store, server_pk_b64),
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daemon=True,
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).start()
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except KeyboardInterrupt:
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print("\nshutdown")
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finally:
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sock.close()
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