added few ctfs

cscg25/crypto/intro3/main.py

@@ -0,0 +1,28 @@
+import os
+import struct
+
+BITS = 56
+
+FLAG = os.getenv("FLAG", "CSCG{TESTFLAG}")
+
+A = int.from_bytes(os.urandom(BITS//8), "little")
+B = int.from_bytes(os.urandom(BITS//8), "little")
+SEED = int.from_bytes(os.urandom(BITS//8), "little")
+
+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
+
+def main():
+    print("Here are some random numbers, now guess the flag")
+    rng = gen_random(SEED, BITS, 0xFF)
+    for i in range(len(FLAG)):
+        print(next(rng) ^ ord(FLAG[i]))
+
+if __name__ == "__main__":
+    main()