added few ctfs

cscg25/crypto/intro3/exploit.py

@@ -0,0 +1,45 @@
+from z3 import Solver, BitVec, sat
+
+def rng(x, size):
+    return (x*A+B) & ((2**size)-1)
+
+def gen_random(seed, bits, mask):
+    state = seed
+    while True:
+        state = rng(state, bits)
+        yield state & mask
+
+A = BitVec("A", 56)
+B = BitVec("B", 56)
+SEED = BitVec("seed", 56)
+BITS = 56 
+MASK = 0xFF
+
+state = SEED 
+
+with open("./msg.txt", "r") as f:
+    nums = [int(n) for n in f.readlines()[1:]]
+    print(nums)
+
+flag_bytes = [BitVec(f'flag_{i}', 56) for i in range(142)]
+
+solver = Solver()
+
+for i, n in enumerate(nums):
+    state = rng(state, BITS)
+    cur_num = state & MASK
+    solver.add(n == cur_num ^ flag_bytes[i])
+    solver.add(flag_bytes[i] >= 32, flag_bytes[i] <= 126)
+
+if solver.check() == sat:
+    model = solver.model()
+    flag = ''.join([chr(model[flag_bytes[i]].as_long()) for i in range(142)])
+    print(model)
+    print(flag)
+else:
+    print("Not solveable")
+
+
+
+
+