feat: Cryptgeon client with AES-GCM client-side encryption

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

openvpncertupdate.py

@@ -257,6 +257,58 @@ def build_ovpn(
     return str(out_file.resolve())
 
 
+# ============================================================
+# === CRYPTGEON ===
+# ============================================================
+
+
+class CryptgeonError(Exception):
+    pass
+
+
+def create_note(content: str, base_url: str) -> str:
+    """AES-256-GCM encrypt content, POST to Cryptgeon, return one-time URL.
+
+    Encryption matches the Cryptgeon browser client:
+      raw_key (32 bytes) → URL fragment (base64url, no padding)
+      aes_key = SHA-256(raw_key) → AES-256-GCM
+      payload = list(nonce + ciphertext)
+    """
+    if AESGCM is None:
+        raise CryptgeonError("cryptography package not installed (pip install cryptography)")
+
+    raw_key = os.urandom(32)
+    aes_key = hashlib.sha256(raw_key).digest()
+    nonce   = os.urandom(12)
+    aesgcm  = AESGCM(aes_key)
+    ciphertext = aesgcm.encrypt(nonce, content.encode("utf-8"), None)
+
+    payload = json.dumps({
+        "contents": list(nonce + ciphertext),
+        "views": 1,
+        "type": "text",
+    }).encode("utf-8")
+
+    api_url = base_url.rstrip("/") + "/api/notes/"
+    req = urllib.request.Request(
+        api_url,
+        data=payload,
+        headers={"Content-Type": "application/json"},
+        method="POST",
+    )
+    try:
+        with urllib.request.urlopen(req) as resp:
+            body = json.loads(resp.read())
+    except urllib.error.HTTPError as exc:
+        raise CryptgeonError(f"Cryptgeon API returned {exc.code}: {exc.reason}") from exc
+    except Exception as exc:
+        raise CryptgeonError(f"Cryptgeon request failed: {exc}") from exc
+
+    note_id      = body["id"]
+    key_fragment = base64.urlsafe_b64encode(raw_key).rstrip(b"=").decode()
+    return f"{base_url.rstrip('/')}/#/note/{note_id}/{key_fragment}"
+
+
 # (remaining sections added in later tasks)
 # ============================================================
 

tests/test_cryptgeon.py

@@ -0,0 +1,48 @@
+import json
+import pytest
+from unittest.mock import patch, MagicMock
+from openvpncertupdate import create_note, CryptgeonError
+
+
+def mock_response(body: bytes):
+    resp = MagicMock()
+    resp.read.return_value = body
+    resp.__enter__ = lambda s: s
+    resp.__exit__ = MagicMock(return_value=False)
+    return resp
+
+
+@patch("openvpncertupdate.urllib.request.urlopen")
+def test_returns_url_with_id(mock_open):
+    mock_open.return_value = mock_response(b'{"id":"abc-123"}')
+    url = create_note("secret", "https://cg.example.com")
+    assert "abc-123" in url
+    assert url.startswith("https://cg.example.com/#/note/abc-123/")
+
+
+@patch("openvpncertupdate.urllib.request.urlopen")
+def test_posts_to_correct_endpoint(mock_open):
+    mock_open.return_value = mock_response(b'{"id":"x"}')
+    create_note("hello", "https://cg.example.com")
+    req = mock_open.call_args[0][0]
+    assert req.full_url == "https://cg.example.com/api/notes/"
+    body = json.loads(req.data)
+    assert isinstance(body["contents"], list)
+    assert body["views"] == 1
+    assert body["type"] == "text"
+
+
+@patch("openvpncertupdate.urllib.request.urlopen")
+def test_raises_on_http_error(mock_open):
+    import urllib.error
+    mock_open.side_effect = urllib.error.HTTPError("", 500, "Error", None, None)
+    with pytest.raises(CryptgeonError, match="500"):
+        create_note("secret", "https://cg.example.com")
+
+
+@patch("openvpncertupdate.urllib.request.urlopen")
+def test_different_passwords_give_different_urls(mock_open):
+    mock_open.return_value = mock_response(b'{"id":"same"}')
+    url1 = create_note("pass1", "https://cg.example.com")
+    url2 = create_note("pass2", "https://cg.example.com")
+    assert url1 != url2