Test all the syncs

chals/crypto/test_chal/Dockerfile

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+FROM ubuntu:20.04
+
+RUN apt-get update && apt-get install -y socat python3
+
+RUN adduser chal
+
+RUN mkdir -p /chal
+WORKDIR /chal
+
+COPY chal.py flag.txt ./
+RUN chmod 555 chal.py
+USER chal
+
+CMD socat -T60 TCP-LISTEN:1337,fork,reuseaddr EXEC:"python3 -u chal.py",stderr

chals/crypto/test_chal/chal.py

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+import hashlib
+import os.path
+
+if __name__ == '__main__':
+    print("Welcome to my neutron collider. Using state of the art technology, I will smash two strings into each other. I call this ability 'string theory'.")
+    print("Weird stuff happens when they collide... the energy of the collision is so high it creates another third string that my research team is calling a 'flag'. ")
+    print("BUT!!!! To save resources, your strings must be sigpwny (TM) branded!!!")
+
+    x = input("string 1 > ").encode('utf8','surrogateescape')
+    y = input("string 2 > ").encode('utf8','surrogateescape')
+
+    if not x.startswith(b'sigpwny{') or not y.startswith(b'sigpwny{'):
+        print("Hey! I'm on a tight budget here. I need to reinvest as much as possible into my collider. Make sure both strings are sigpwny (TM) branded.")
+
+    if hashlib.md5(x).hexdigest() == hashlib.md5(y).hexdigest():
+        print(open('flag.txt').read() if os.path.isfile('flag.txt') else 'Error: no flag file found')
+    else:
+        print("Yeah those strings didn't collide. Maybe collide two different strings...")

chals/crypto/test_chal/challenge.yml

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+name: "TESTCHALLLLLLLLLLLLLLL"
+author: Pete
+category: Crypto
+description: |-
+  My research team has toiled away to create a state-of-the-art neutron collider (Mark Demolisher V - MD5, for short).
+  Can you get two neutrons to collide?
+
+  `nc chal.fallctf.sigpwny.com 6001`
+
+  **author**: Pete
+value: 500
+type: dynamic
+tags:
+  - medium
+extra:
+  initial: 500
+  decay: 150
+  minimum: 100
+flags:
+  - sigpwny{md5_is_broken_and_now_im_broke}
+files:
+  - chal.py
+hints:
+  - We need to execute a certain type of a md5 hash collision attack.
+  - Look for a tool to pull off a "md5 same prefix hash collision" attack.
+  - Use [HashClash](https://github.com/cr-marcstevens/hashclash)
+state: hidden

chals/crypto/test_chal/flag.txt

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+sigpwny{md5_is_broken_and_now_im_broke}

chals/crypto/test_chal/solution.sh

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+#!/bin/bash
+(cat collision1.bin; echo ""; cat collision2.bin; echo "";) | python3 chal.py