feat: add worker AES-256-GCM crypto matching the web envelope

worker/lyra_worker/crypto.py

@@ -0,0 +1,37 @@
+import base64
+import json
+import os
+
+from cryptography.hazmat.primitives.ciphers.aead import AESGCM
+
+
+def _key() -> bytes:
+    b64 = os.environ.get("LYRA_SECRET_KEY")
+    if not b64:
+        raise RuntimeError("LYRA_SECRET_KEY is not set")
+    k = base64.b64decode(b64)
+    if len(k) != 32:
+        raise RuntimeError("LYRA_SECRET_KEY must decode to 32 bytes")
+    return k
+
+
+def encrypt_secret(plaintext: str) -> str:
+    iv = os.urandom(12)
+    full = AESGCM(_key()).encrypt(iv, plaintext.encode("utf-8"), None)  # ct || tag(16)
+    ct, tag = full[:-16], full[-16:]
+    return json.dumps(
+        {
+            "iv": base64.b64encode(iv).decode(),
+            "ct": base64.b64encode(ct).decode(),
+            "tag": base64.b64encode(tag).decode(),
+        }
+    )
+
+
+def decrypt_secret(envelope: str) -> str:
+    e = json.loads(envelope)
+    iv = base64.b64decode(e["iv"])
+    ct = base64.b64decode(e["ct"])
+    tag = base64.b64decode(e["tag"])
+    pt = AESGCM(_key()).decrypt(iv, ct + tag, None)  # AESGCM expects ct || tag
+    return pt.decode("utf-8")