crypto: halloween

crypto/halloween/halloween/Dockerfile

@@ -0,0 +1,15 @@
+FROM python:3.11-alpine
+
+RUN apk --update add socat \
+	&& adduser -D --home /app user \
+	&& pip3 install gostcrypto
+
+COPY --chown=user . /app
+
+RUN chmod 755 /app/entry.sh /app/chall.py
+
+WORKDIR /app
+
+EXPOSE ${LISTEN_PORT}
+
+ENTRYPOINT ["/app/entry.sh"]

crypto/halloween/halloween/chall.py

@@ -0,0 +1,16 @@
+#!/usr/bin/env python3
+import gostcrypto
+import os
+
+with open("flag.txt", "rb") as f:
+    flag = f.read()
+
+key, iv = os.urandom(32), os.urandom(8)
+cipher = gostcrypto.gostcipher.new(
+    "kuznechik", key, gostcrypto.gostcipher.MODE_CTR, init_vect=iv
+)
+
+print(f"It's almost Halloween, time to get sp00{cipher.encrypt(flag).hex()}00ky 👻!")
+
+while True:
+    print(cipher.encrypt(bytes.fromhex(input())).hex())

crypto/halloween/halloween/entry.sh

@@ -0,0 +1,6 @@
+#! /bin/sh
+
+while :
+do
+    socat TCP-LISTEN:${LISTEN_PORT},forever,reuseaddr,fork EXEC:'/app/chall.py' 2>/dev/null
+done