failed miserably at hack.lu

2025/hack.lu/crypto/manual/public/server.py

@@ -0,0 +1,99 @@
+import secrets
+import random
+import os
+
+from typing import Callable
+
+FLAG = os.getenv("FLAG") or "flag{this_is_a_test_flag_:D_>.<}"
+
+class InstructionManual:
+    STEP_COUNT = 40
+    PIECE_SIZE = 256
+    PIECE_COUNT = PIECE_SIZE // 8
+    BIGGEST_PIECE = 2**PIECE_SIZE - 1
+
+    _steps: list[Callable[[int], int]]
+    
+    def __init__(self):
+        step_types = [self.step_screw_in, self.step_turn_around, self.step_hammer_together]
+        prefix = [x() for x in step_types]
+        suffix = [x() for x in step_types[::-1]]
+        self._operations = prefix + [random.choice(step_types)() for _ in range(self.STEP_COUNT)] + suffix
+
+    def build(self, value: bytes) -> bytes:
+        assert len(value) == self.PIECE_COUNT, "These pieces don't seem to be the correct size :("
+        wip_furniture = int.from_bytes(value, "big")
+        for op in self._operations:
+            wip_furniture = op(wip_furniture)
+
+        return wip_furniture.to_bytes(self.PIECE_COUNT, "big")
+
+    @classmethod
+    def step_screw_in(cls):
+        screw_tight = secrets.randbits(1) == 1
+        screw_amount = secrets.randbelow(cls.PIECE_SIZE)
+        def _inner(value: int) -> int:
+            if screw_tight:
+                return ((value >> screw_amount) | (value << (cls.PIECE_SIZE - screw_amount))) & cls.BIGGEST_PIECE
+            else:
+                return ((value << screw_amount) | (value >> (cls.PIECE_SIZE - screw_amount))) & cls.BIGGEST_PIECE
+            
+        return _inner
+
+    @classmethod
+    def step_turn_around(cls):
+        def _inner(value: int) -> int:
+            return int.from_bytes(value.to_bytes(cls.PIECE_COUNT, "little"), "big")
+
+        return _inner
+
+    @classmethod
+    def step_hammer_together(cls):
+        required_hammer = secrets.randbits(cls.PIECE_SIZE)
+        def _inner(value: int) -> int:
+            return value ^ required_hammer
+        
+        return _inner
+
+def main():
+    assert len(FLAG) == InstructionManual.PIECE_COUNT, "incorrect flag length!!"
+    
+    instruction_manual = InstructionManual()
+    print("Here at FLUX, we always strive to include the latest technological advancements in our products.")
+    print("This instruction manual has been generated just for you! But we don't know which pieces are needed to actually construct it...")
+    print("Can you help us figure out how it all fits together?")
+    print()
+
+    max_count = 300
+
+    print("We've allocated some time for one of our interns to help you with this task.")
+    print(f"They will attempt to follow the instruction manual using pieces you provide, for a maximum of {max_count} attempts.")
+
+    remaining = max_count
+    while remaining > 0:
+        val = input(f"({max_count - remaining}/{max_count}) Please enter your {InstructionManual.PIECE_COUNT} selected pieces as one hex encoded string, or 'finish' to exit early:\n")
+        if val == "finish":
+            break
+
+        try:
+            decoded = bytes.fromhex(val)
+            if len(decoded) != InstructionManual.PIECE_COUNT:
+                print("incorrect piece count.")
+                continue
+
+        except Exception:
+            print("incorrect pieces.")
+            continue
+
+        assembled_furniture = instruction_manual.build(decoded)
+        print("Here is what the intern put together:")
+        print(assembled_furniture.hex())
+
+        remaining -= 1
+
+    print("The intern says they've understood what the manual is supposed to construct now, and to relay you this message:")
+    print(instruction_manual.build(FLAG.encode()).hex())
+    print("Thanks for your help!")
+
+if __name__ == "__main__":
+    main()