Init. Commit

qualifiers/tagpreview-crypto-easy/solve/solve.py

@@ -0,0 +1,43 @@
+#!/usr/bin/env python3
+import json
+import re
+import sys
+import urllib.request
+
+
+def get_bytes(url: str) -> bytes:
+    with urllib.request.urlopen(url, timeout=5) as response:
+        return response.read()
+
+
+def post_bytes(url: str, body: bytes) -> dict:
+    req = urllib.request.Request(
+        url,
+        data=body,
+        method="POST",
+        headers={"Content-Type": "application/octet-stream"},
+    )
+    with urllib.request.urlopen(req, timeout=5) as response:
+        return json.loads(response.read().decode())
+
+
+def solve(base_url: str) -> str:
+    base = base_url.rstrip("/")
+    record = bytearray(get_bytes(base + "/sealed-note"))
+    record[-1] ^= 1
+    result = post_bytes(base + "/inspect", bytes(record))
+    preview = result.get("preview", "")
+    match = re.search(r"caplag\{[^}]+\}", preview)
+    if not match:
+        raise RuntimeError(f"flag not found in preview: {result}")
+    return match.group(0)
+
+
+def main() -> None:
+    if len(sys.argv) != 2:
+        raise SystemExit(f"usage: {sys.argv[0]} http://host:port")
+    print(solve(sys.argv[1]))
+
+
+if __name__ == "__main__":
+    main()